Troubleshooting '68 Mustang: Hot Wiring and Checking Ignition System

[Big Block]

Averagesupernova,
Thanks for the info...and I will find this burnt sucker!

Ranger Mike,
Results from jumping the "+"(positive) side of the battery to the heavy duty starter cable on the large lug of the solenoid = a small spark (but no cranking of the starter).

Where do I go from here guys?...What do I inspect next?...

 

[nucleus]

Where do I go from here guys?...What do I inspect next?...

Do a Voltage Drop Test. It is by far the best test for a starter circuit.:

http://www.sacskyranch.com/voltage.htm
http://www.youtube.com/watch?v=XhRPLgH6uZg&feature=related
http://www.youtube.com/watch?v=ry68G0C2Fyc&feature=related

Goggle it for more information.

Re your ammeter . The black lead for the oil pressure comes from the instrument voltage regulator. You may have fed 12 volts to your gauges, Do any of the gauges work?
The wiring diagrams are available here:

http://www.themustangshop.com/resources.cfm

 

[Ranger Mike]

the above video is good..you should have a huge strong spark when you jumped the battery to the starter cable..i would check the starter cable ..especially at the starter connection..make sure it has not frayed or loosened up in the wire lug that is on the end of the starter cable...worst comes to worst..pull the starter and have it checked at NAPA or Autozone...

 

[nucleus]

“My car is a 4-speed manual shift and doesn't have a neutral safety switch (automatics only).”

That does not mean that the switch is not there. On manuals the neutral safety switch has to be jumped permanently. There is a Red-Blue wire running from the S (start) terminal of your ignition switch to the starter solenoid. This wire goes through the neutral switch. You should get power when the key is held in the start position. To bypass the key you run a jumper wire from battery side of solenoid (large wire) to the small lug where the Red-Blue wire goes on. Warning: make sure car is in neutral, park brake on and disable ignition.

“Battery is good and strong 12.48V”
Just because it has 12.8 volts does not mean it’s good. Measure across the battery posts under load. For instance, when you try the starter, the voltage should not drop below 9.6 volts. If the car hasn’t been started in six months there is a good chance it will not have enough juice to turn the starter. It may not be the problem but at least you eliminated it.

 

[Averagesupernova]

All this advice is good but I think we should start where the smoke got loose. Something burned under the dash. It doesn't matter if the battery isn't good enough to spin a starter at this point. We know it was good enough to burn a wire off or open a fuse link or toast the ammeter and my assumption is that it is still that good. When we get power to the accessories and headlights we will at least know that a large portion of the cars electrical system is working.

 

[Big Block]

Averagesupernova,
You're right on the money. My alternator gauge is smoked. Got a live reading (from the test light) on the lug nut with the heavy duty alternator gauge wire, but nothing from the other lug nut.
I have to order a new gauge from the States. It will take some time to get here, so I will post back in a couple of weeks with all the other suggested "tests" results.

 

[nucleus]

According to the wiring diagram from themustangshop that I posted earlier, there is a yellow and a red wire going to the ammeter. Both of these wires go to the same plug (different terminals) then both end up near the battery side of the starter solenoid. They do not connect to any other wires.

It was the black wire that you said was crossed with the oil pressure wire and did the damage, so it had power then! Did you forget to install it when you had the wires off the starter solenoid? If not you should trace the wires back to see why you have no power.

It sounds like all you have is a test light, is that correct? With an ohmmeter you could disconnect the battery and read across the ammeter and check it before ordering a new one.

 

[nucleus]

Actually you should only get power to one terminal of the gauge at a time. With the engine not running the power should be on the black wire (with reference to ground). The yellow wire finds ground eventually through the ignition switch and some accessory, so I think it is normal to only get power on the black wire with engine off.

With the engine running the yellow wire will be more positive than the black. The black will then be the ground.

Re measuring across the gauge with ohmmeter you need to remove one lead. An ampere gauge is really a millivolt gauge connected to a shunt.

 

[Averagesupernova]

Nucleus, if there are large heavy wires that attach to the ammeter gauge, then the shunt is internal the same way it is on a multimeter. You should never ever ever ever ever have power on one side of an ammeter and not on the other. If this is the case then the ammeter is toast. Getting power through an ammeter of any kind only requires that the shunt is intact whether it is internal or external. It does not matter if the 'millivolt gauge' as you call it is even in circuit. Nucleus, so far I think you have only confused the OP.
-
To the OP: Now I realize that by my saying this questions my earlier advice but if I were you I would temporarily bypass the ammeter to make double sure so you don't needlessly purchase a new gauge. Bypassing the gauge should make your car work like it has a new gauge, but obviously the gauge won't read anything. Not only that, you can proceed to trouble shoot anything else you have wrong on the vehicle while bypassed. Just my 2 cents.

 

[nucleus]

Averagesupernova
“You should never ever ever ever ever have power on one side of an ammeter and not on the other.”

That is not what I said! I said it seeks ground through the yellow wire when the engine is not running. However, there are several paths involved, including the key being on for some of them. You will not be able to read the this power with a test light and may change the gauge for nothing.

“Nucleus, so far I think you have only confused the OP.”

I don’t think that is possible. The OP has not answered any of my questions so I doubt he/she has even read them. I feel like I am talking to myself! He needs to find someone that knows how to trace wires or he will just keep changing parts, and that can get expensive if you have to order them in.

The first wire to trace is the BLK-YELLOW from battery. It ends up at a fuse, which if open, will prevent door lights and courtesy lights from working. I agree with you re bypassing gauge for now.

 

[Averagesupernova]

Actually you should only get power to one terminal of the gauge at a time.

So what did ^^^^^^this^^^^^^^^ mean? If you have power on one side of an ammeter and not the other then the gauge is toast providing it has an internal shunt, and if external, then the shunt is fried. There is no more to this story. A test light will show this up easily. The question is if it is an internal shunt or not. I suspect after looking at the diagram that it is an external shunt. Yellow wire #37 in the diagram. There still is really only one path and that is through the yellow wire. I am suprised that they used a heavy wire to the gauge itself if it is an external shunt. OP, I hope you are watching this.
-
What are you calling the black/yellow wire that ends up at a fuse? If it is what I think it is, this is not a fuse. Cars of this era didn't usually have any fuses in the charging system or directly off the battery. There were fuses for accessories and lights but that's about it. Not even for the ignition system.

 

[Big Block]

Averagesupernova
The OP has not answered any of my questions so I doubt he/she has even read them. I feel like I am talking to myself!

This is your OP speaking Nucleus. By the way, what does OP mean?...Other Person? Other Party? or Outside Party?...Please clarify. I was waiting for the mud to settle before speaking with you.

This is the wiring setup to the alternator gauge and the oil pressure gauge as it stands now.
1) ALTERNATOR GUAGE: Looking at the back of the gauge in a normal upright position -
Left lug/post = small red and violet wire Right lug/post = heavy duty "live" black wire
Bottom lug post = a ground wire

2) OIL PRESSURE GUAGE: Looking at the back of the gauge in a normal upright
position.
Left lug/post= heavy duty black wire Right lug/post = small black wire
Bottom lug/post = a ground wire

Is this setup correct?
O:
What reading in ohms should I get when measuring across the gauge with an ohmeter(after I've removed one lead?

Averagesupernova,
Q:
How do you bypass the ammeter making my car work like it has a new guage? (posted in your 2nd last message at 11:21 AM)

 

[Averagesupernova]

Bigblock, do you understand the drawing in post number 4 in this link: http://mustangforums.com/forum/classic-mustangs/596726-amp-gauge-wiring.html
?

I think nucleus and I have come to the conclusion that it uses an external shunt. However, you still should show power on both sides of the ammeter. The yellow hilighted wire in the drawing is considered the shunt and the gauge in your dash measures the voltage dropped (lost) in that section of wire. Seems impossible at first but it is so. You should be able to see from the drawing that the gauge itself is not required for your vehicle to operate. I may have slightly misinformed you in the past and am sorry for that. So can you see how the yellow hilighted wire could cause what you are experiencing if it were burned off? The logical place to start of course is under the dash. However, the smoke you seen from under the dash could have come from the gauge AFTER the shunt was burned open under the hood. I would think this would put a full 12 volts across the gauge in your dash and could cause damage.
-
Would you agree that disconnecting the main disconnect connectors shown on the diagram should NOT cause a loss of power at the main alternator lug? Maybe you should do this and troubleshoot from there? It would be a bit easier to keep it straight in your own mind knowing to ignore everything under the dash.
-
BTW, OP means original poster.

 

[Big Block]

Averagesupernova,
Q:
How do you bypass the ammeter making my car work like it has a new guage? (posted in your 2nd last message at 4:03 AM)

Averagesupernova and/or Nucleus,

1) How do I bypass the ammeter gauge to make my car work (without the ammeter).

2) Is the below posted literal description setup of the wiring for the ammeter, and oil pressure guages correct? Please verify...

Nucleus,
This is the wiring setup to the alternator gauge and the oil pressure gauge as it stands now.
1) ALTERNATOR GUAGE: Looking at the back of the gauge in a normal upright position -
Left lug/post = small red and pale violet wire Right lug/post = heavy duty "live" black wire
Bottom lug post = a ground wire

2) OIL PRESSURE GUAGE: Looking at the back of the gauge in a normal upright
position.
Left lug/post= heavy duty black wire Right lug/post = small black wire
Bottom lug/post = a ground wire
Is this setup correct?

Nucleus,

I will do the "Voltage Drop Test" and your other tests as soon as we clear up this ammeter issue first.

1) How many ohms should I read when testing across the ammeter lug/posts (with one lead removed...WHICH LEAD?..and is the battery is NOT hooked up?...

 

[Averagesupernova]

I think you have missed the point. I clearly stated that you don't even need the gauge installed for your vehicle to work if the system uses an external shunt which nucleus and I have come to the conclusion that this is the case. I may have misinformed you earlier while thinking that there was no external shunt and that ALL the current has to pass through the gauge itself and am sorry for this. The test that shows power only on one side of the gauge is still a valid test and indicates something is open somewhere. I cannot tell you if your description of wire colors is correct. I can only go by what I know from experience and what is drawn in the link that nucleus was nice enough to post. So if you are willing to agree that the drawing I refer to is valid, can you see why I ask you to forget about what is going on under the dash for the moment and look at the hilighted yellow wire in the drawing in the link? http://mustangforums.com/forum/classic-mustangs/596726-amp-gauge-wiring.html
-
Do NOT bypass the gauge itself under the dash. One wire that connects to it is not heavy enough to carry the load based on your description of said wire. You need to be concerned with the yellow hilighted wire in the diagram.
-
If you need more explanation on something I've posted just ask. If you don't understand why the gauge is not needed just say so. No harm in not knowing something, we know you came here for a reason.

 

[Ranger Mike]

Averagesupernova was kind enough to supply the wiring diagram.
Let us start at the battery..one side is ground ( triangle like symbol) to other is the hot (+ ) side. It is connected to the starter solenoid or relay with a big number 2 cable bolted to a huge lug. On this lug are two additional wires..see diagram..625 that runs to your Ammeter and 37 (yellow) that runs to junction connection where one side splits off to the alternator (37 red) one wire runs to the main connector and wire 654 blue one wire runs to the Ammeter... THRU and fuse or fusible link as indicated just after the junction...) The ammeter is a meter that indicates if the alternator is charging and in order to work it must be in series or in line with the circuit so the alertnator puts out voltage (V=IR) and the current is displayed on the gage.

Back to the STARTER - the starter has one ground wire ( triangle like symbol) and one large number 2 wire connected to the other side of the starter relay.
The starter relay is just a switch activated by 12 volts supplies to the S terminal via the 32 wire. The 32 wire is activated in the turn and hold position of the ignition key. If every thing is operating correctly, when you jump 12 volts to the S terminal, it connects the switch and the starter should spin..like wise if you connect the 12 volt number 2 cable from the battery directly to the large number 2 cable the starter should spin.
The I terminal on the starter relay ( wire 262) is connected to the ignition key ( when key is in the ON position..( when your radio plays) and is also connected to the + side of the ignition coil. ( there is also an Accessory position on the ignition key, opposite of the On position..used for accessories like the radio.This was done to keep idiots from burning out points and ignition coils when they left 12 volts running to these ignition parts for hours while they were trying to get into Mary Jane rotten crotch's pants at the drive in movie).
anyway, you can hot wire the car by simply jumping 12 volts to the + side of the coil and actuating the starter by jumping the two large number 2 cables...
now you know..
P.S. don't call be if you get caught boosting some ones car with this technique..
rm

 

[Big Block]

Good one rm. You made me laugh with the line about the guys burning out their points and ignition coils while trying to get into mj's "ro__en" crabby cake. A sense of humor...I like that.

It all makes sense now the way you, Averagesupernova and Nucleus have explained it (along with the wiring diagrams). I feel confident now with all this ammo (information) that I can trace the proper wires and find the burnt solution.

I will troubleshoot this long weekend, and post back with the results. Have a great weekend guys.





__________________________________________
Keep her between the ditches, 10-4, over and out

 

[Big Block]

Well I thought that some "HOOO-RAW's" would be in order, but it's still premature. I must say that this problem is a defiant one - right to the bitter end!

Progress Report:
I have been unable to locate the yellow "shunt" wire (#37) under the hood. Next move remove the instrument cluster and check under the dash as well as the constant voltage regulator.
I have bypassed the alternator gauge by wrapping the alternator wires together and insulating with electrical tape (that is HD "live" black wire and the black return wire. The oil pressure gauge has also a HD "live" black wire with a red-white return wire).
I also found 3 wires under the hood that have no continuity at the connector (2 red, and 1 white-red). These are for the coil and oil sender unit, and appear just after a 'disconnect block' of spagetti-like wire. I have spliced and by-passed the bad sections, but the main red still has no continuity.
"Results =
The "idiot alternator light" on the dashboard comes on when I hook up the battery terminals...ignition is in the OFF position. The light remains "ON" even when ignition is set to "ACC., ON or OFF"...Bizz-arrro!...

Q: When removing the speedo cable (from the back of the instrument cluster) there is a 5/8" locking nut holding the cable in place. As I can only feel my way (can't see a damn thing inside there), is the locking nut totally removed with cable still attached, or is the cable detachable from the nut?

 

[Averagesupernova]

Without actually physically looking at your car I don't think I can be of much more help without continually repeating myself. Do you have a reason to believe that the diagram that has been posted on a link that nucleus was kind enough to provide is not an accurate representation of your car? If you believe that diagram is correct then why do you continue to mess around under the dash when the diagram clearly shows that the harness can be completely disconnected from the passenger compartment and provide continuity from the battery to the alternator? When troubleshooting we always try to simplify and isolate. You are doing the opposite.

 

[Ranger Mike]

speedo nut is permanently secured to the cable..simply unscrew it..we did this a lot in the old days to ' save mileage"..i f the speedometer was ' jumping around " when at speed, now is a good time to lubricate the cable..it pulls out of the shielded cable and get some speedometer lube at NAPA or Autozone..ref: trouble shooting..i think you have spliced into a live 12 volt wire ..that is why the idiot light stays on..this should only be on when ignition key is at "on" position...you need to fix this..

I also found 3 wires under the hood that have no continuity at the connector (2 red, and 1 white-red).Do they have 12 volts with key in ON position?

These are for the coil and oil sender unit, and appear just after a 'disconnect block' of spagetti-like wire. I have spliced and by-passed the bad sections, but the main red still has no continuity.

 

[6Stang7]

I'm not sure if an answer was given regarding hot wiring the 68, but in case it wasn't, here's how.

The start relay has four posts (shown below), with post #1 on the far left, post #2 on the bottom left, #3 on the bottom right, and #4 on the far right.

[PLAIN]http://www.publicityx.com/major/cart/cart/images/iginition/5678fordstartersolenoid.jpg

Use a piece of wire to connect post #1 to #3; this will act as if the ignition key was in the "RUN" position. Use a screwdriver to bridge post #1 to #2; this will act as if the key was in the "START" position. Once the engine fires up (if all you're wiring is good), remove the screwdriver and the car should run.

If it's been determined that there is an issue with the ignition system, then I'll read up and give my $0.02 if I have any (as my name might suggest, I have a lot of experience with the 67/68's )

 

[Big Block]

Thanks for your input 6Stang7. This is perrr-fect. Just what I was looking for.
bb.

 

[Big Block]

Averagesupernova, Nucleus and Ranger Mike,

Is this the 'Holy Grail' that we have been looking for? The elusive, external shunt wire!. If yes, give me your feedback. If no, I'll keep looking.

_______________
No Guts - No Glory

 

[Averagesupernova]

Beware. The jumper being put between 1 and 3 does a little more than bypass the ignition switch. It's purpose is to bypass the ballast resistor on points ignition systems during cranking. When the starter is cranking the battery voltage is pulled down considerably. Normally the ballast resistor drops about 6 volts so the coil is actually running on 6 volts during normal running. It is designed for this. For the few seconds during cranking the ballast resistor is bypassed by the terminal 3 in the diagram in post #56. This gives easier starting due to a hotter spark. This is not a problem for a few seconds during starting. However, your coil will not handle it for very long.
-
I don't see how this info can be very useful to you Bigblock since you have proven many posts ago that the exact thing described in post #56 does not cause the starter to turn on your mustang. You are back where you started already and my advice from several posts ago still stands.
-
Edit: Posted at about the same time Bigblock.
-
The diagram previously posted should be enough to go on provided you have no reason to believe it is wrong. It is more application specific than the diagram you posted in #58.

 

[Big Block]

Averagesupernova,

According to your previous posts #46, #48 and #50, I am looking for a (#37) yellow "hi-lighted" wire (as in the posted diagram) which acts as an external shunt to the ammeter. Please examine post #58 in closer detail. It has the external shunt shown in the diagram. Isn't the external shunt what I'm looking for...

 

[Averagesupernova]

Yes the external shunt is what you are looking for. Why are you dragging a new diagram into this? The diagram in this link:
http://mustangforums.com/forum/classic-mustangs/596726-amp-gauge-wiring.html
-
shows it just fine. In fact it is in better detail. If this wire #37 is intact you will have power at the large terminal on the alternator even with the connectors on the firewall unhooked. This is where you need to be looking. I don't know what color it is in real life. I know it has to carry complete charging current so I would say back in the day with the size charging system that car had possibly a #8 wire.
-
Edit: Do you have a reason to believe the diagram in the link I gave is inaccurate?

 

[Big Block]

Averagesupernova,
Had work I had to attend to. This is the status so far.

I have completely rebuilt the alternator wiring harness-brand new (including the shunt). I have power to both sides of the ammeter (unlike in posts #12 and #17). Also, I have power to the large lug (#37) at the alternator (reference post #60).

Although I did check the ignition switch wiring with a continuity check their was 1 female pin hole (B, for #37) that was brown around the edge. So, I'm buying a new ignition switch wiring harness-just to be safe...

BTW, how does one place a picture in the left-most margin under your name "Big Block"?...

P.S. The wiring diagrams are just fine, but the wire color codes are different.

 

[Averagesupernova]

Ok so you have replaced a significant part of the wiring in question. What specifically is not working on your car now?

 

[Big Block]

Averagesupernova,
So, I'm buying a new ignition switch wiring harness-just to be safe...

BTW, how does one place a picture in the left-most margin under your name "Big Block"?...

P.S. The wiring diagrams are just fine, but the wire color codes are different.

Results = No power:
. at the ignition switch (or cranking)
. no courtesy kights
. no radio
. no instrument panel lights
. no parking or headlights

 

[Averagesupernova]

Start at the connector on the firewall from the outside. Verify you have power on the pins you believe you are supposed to. Then go inside and do the same thing. There is most likely just ONE connection that is open. The test from the outside to the inside should show this up.
-
Refer to the diagram I linked in post #61. There is a node of 4 wires next to the firewall connector coming together in which one of them is #37 shunt hi-lighted yellow. The wire that goes through the connector and is labeled 37 which then goes off the diagram is most likely the one you need to follow.