Why are the trailer lights on jeep 2 not functioning properly?

In summary, the issue discussed in the conversation is about troubleshooting why one jeep is not powering all lights on a trailer, while the other jeep is able to successfully operate the lights. The conversation includes various theories and suggestions, including checking the ground connection, a possible high resistance in the positive supply, and a poor wiring job. The person investigating eventually discovers two problems - a bad wiring job and damaged wires at the socket where the trailer plugs in. They plan to purchase new parts to fix the issue.
  • #1
phlegmy
120
0
hey guys, i could as easily post this in an automotive type forum but I'm not a member of any! no specific car knowledge nescessary!

Here is the problem
Where I'm working now, there are two jeeps and one Car type trailer
jeep 1 operates all the lights on the trailer successfully
jeep 2 will only operate the indicators, no other trailer lights function at all

i was given the task of investigating why jeep 2 will not power all lights (side lights brake lights etc)
i have determined the trailer and jeep1 are wired correctly

to determine if jeep 2 is wired conventionally i used a multimeter while getting someone to turn on various indicators, lights etc
all terminals on the socket produced a voltage when they should, so i reasoned it was wired correctly


now here's the situation:
i connect the voltmeter across the grnd and tail lights on the lights socket on the jeep with the trailer lights plugged OUT.
with the jeep lights on, this shows a few volts (cant remeber how many maybe 8-11v) as i'd expect
now i plug in the trailer lights, the voltage drops to ZERO!

so i think, hmmm what could be causing this?
could it be that the wire is grounded or shrt ccted furter up on the jeep end... but i figured that if it were, i would not read such a high voltage with the trailer plugged out as 99% of the voltage would drop across the short?

so secondly i considered that there is some kind of high resistance somewhere along the positive supply, i.e. a high resistance in series
so i'd have battery+, high reistance, bulb, battery-
i figure that this high reistance in series wouldn't affect the voltage I'm reading across the terminals. but when the cct is closed (i.e. i plug in my trailer lights) 99% of my voltage drops across the big resistance fault, leaving only a few mV across my bulb, or even ZERO.

IS MY THINKING CORRECT and if so does anyone know how such a big resistance can suddenly appear (the jeep did function with trailer lights previously I'm told) or is there another type of fault that could cause this to happen.

in any case thanks for reading and i'd be interested to read any replies!
james
 
Engineering news on Phys.org
  • #2
I'm a little too drunk and too rushed for time (pool match in 1/2 hour) to properly read your post. I'll try again later. For now, though, having lived through a horrendous few months working at a U-Haul outlet (as an adjunct to my real job at the same place), I would recommend that you run an auxilliary ground from the trailer to the vehicle. You can't trust the ones that come with the harness. Just run a nice heavy (#10 or better) wire from the vehicle frame to the trailer frame and see if it helps.
 
  • #3
Danger is probably on the right track. Some circuits will have power on one side of the bulb and a switch grounds the other side of the bulb. No ground, no light.
 
  • #4
thanks guys
no joy I'm afraid
i'm pretty sure all lights share a common ground and the indicator work fine, so I'm guessing the ground works ok.
i guess i need to know where the socket connection on the jeep is fed from
i suppose its a bank of relays somewhere, but i can't see anything under the bonnet. i'll keep digging and if i turn up with anything i'll post back !
 
  • #5
phlegmy said:
so secondly i considered that there is some kind of high resistance somewhere along the positive supply, i.e. a high resistance in series
so i'd have battery+, high reistance, bulb, battery-
i figure that this high reistance in series wouldn't affect the voltage I'm reading across the terminals. but when the cct is closed (i.e. i plug in my trailer lights) 99% of my voltage drops across the big resistance fault, leaving only a few mV across my bulb, or even ZERO.

IS MY THINKING CORRECT and if so does anyone know how such a big resistance can suddenly appear (the jeep did function with trailer lights previously I'm told) or is there another type of fault that could cause this to happen.

in any case thanks for reading and i'd be interested to read any replies!
james

Yes, your thinking is correct. I'd say this is your problem. How is the trailer connector wired? Most of the time they are spliced into the tail light harness at the back of the vehicle. A poor connection at the splice is most likely the cause and is what you refer to as the 'high resistance'. This is not likely at all a ground problem.
 
  • #6
phlegmy said:
thanks guys
no joy I'm afraid
i'm pretty sure all lights share a common ground and the indicator work fine, so I'm guessing the ground works ok.
i guess i need to know where the socket connection on the jeep is fed from
i suppose its a bank of relays somewhere, but i can't see anything under the bonnet. i'll keep digging and if i turn up with anything i'll post back !

I would validate the ground first.
You can get loopback currents with the multiple lights.
So it isn't unusual to have some work even though the ground is bad.
 
  • #7
well i finally got some time to have a good look at it.
seems there were 2 probs as far as i could see.
the trailer lights seem to be fed straight from the jeeps lights, looks like a bad job.
under the jeep there was a joint in the cable where the wires were joined with "crimps"?
and the whole thing wrapped in insulation tape. anyhow two of theese were pretty much disconnected!, also at the socket where the trailer plugs in, some of the wires seemed to have become brittle and snapped, i undid the trailer plug and twisted the wires onto the jeep wires and all worked, so tomorow morning I'm going to buy some crimps and a new socket for the jeep and i expect all to be well!
 
  • #8
Oh well... I'm use to being wrong. :redface:
I'm glad that you got it sorted out.
 

Related to Why are the trailer lights on jeep 2 not functioning properly?

1. Why are my car trailer lights not working?

There could be several reasons why your car trailer lights are not working. It could be a blown fuse, a faulty wiring connection, a broken light bulb, or a malfunctioning switch. It is best to check each of these components to determine the cause of the problem.

2. How can I fix my car trailer lights problem?

The first step is to identify the specific issue causing the lights to not work. Once you have determined the cause, you can then take the necessary steps to fix it. This could involve replacing a blown fuse, fixing a loose wiring connection, replacing a broken light bulb, or replacing a faulty switch.

3. Can I drive my car with broken trailer lights?

No, it is not safe to drive your car with broken trailer lights. The lights are essential for proper visibility and signaling on the road. Without them, you are putting yourself and others at risk. It is important to fix any issues with your trailer lights before driving your car.

4. How do I prevent my car trailer lights from getting damaged?

To prevent damage to your car trailer lights, make sure to regularly check and maintain them. This includes cleaning them, replacing any broken bulbs, and ensuring all wiring connections are secure. It is also important to properly store and secure your trailer when not in use to avoid any damage.

5. Are LED lights better for car trailers?

LED lights are becoming increasingly popular for car trailers because they are brighter, use less energy, have a longer lifespan, and are more durable. However, they may be more expensive upfront compared to traditional incandescent lights. Ultimately, it depends on personal preference and budget.

Similar threads

  • Introductory Physics Homework Help
Replies
4
Views
328
  • Electrical Engineering
Replies
19
Views
2K
  • Electrical Engineering
Replies
15
Views
565
  • Classical Physics
2
Replies
57
Views
7K
  • Electrical Engineering
Replies
12
Views
1K
  • Electrical Engineering
Replies
20
Views
3K
  • Introductory Physics Homework Help
Replies
3
Views
956
  • Introductory Physics Homework Help
Replies
1
Views
1K
  • Electrical Engineering
Replies
9
Views
9K
  • Thermodynamics
Replies
1
Views
913
Back
Top