I'm trying to put some LED's on our racecar. They're 7 segment LED panels where each segment is 5 LED's with a 220 ohm resistor on the end. The car runs on 12 volts with engine off and 14 with engine on. I have power (Vin) coming off a distribution block, ground also goes to a distribution block. Vin then goes to a 512-KA378R12CTU 12 volt regulator, comes out, and splits off to a screw terminal and to a 511-LD29150DT50R 5 volt regulator, which sends 5 volts to an atmel 328P TQFP package. I have 47uF tantalum, 10 uF tantalum, 1 uF, and 0.33uF capacitors to clean up the input/output voltages. The board works as designed (querying binary coded decimal switches and sending a duplicate readout of the LED panel to an indicator display) with th engine is off (water and fuel pumps don't affect anything), however, once the engine is running, the display goes flat blank, EXCEPT some tiny, tiny pulses (1/500 sec maybe?) every so often. Shut the engine off, goes back to normal. I put my multimeter in ammeter mode, and it recorded 0.1 amps between the Vin lead and a power source. The board pulls 0.4 amps with the ignition off. I put my multimeter on frequency settings, and I get zero hz with nothing on or with all the pumps on. Once the engine is running, I get a 1.2 Khz wave in the system (presumably sinusoidal but without an oscilloscope I don't know...). I was powering the displays from a distribution block very close to the ignition box, so I made a cable going directly to the battery posts (4 ft longer cable). This made things significantly better, now only the 3rd digit (the last on the daisy chain of power) flickers on/off every second or so. I'm guessing I need to make some sort of filter circuit, but I'm not really sure?