Hi folks --

I read through a few other posts on here about what sounds like a very similar issue about very wonky tail light behavior but I'm hoping someone might have some more specific advice on pinpointing the problem......?

I drive a '95 2500 5.7l 4WD extended cab 3/4T pickup.

Here are the symptoms/behaviors (which are intermittent...sometimes everything works perfectly and other times not): With headlights OFF the brake lights work dimly, turn signal causes both tail lights to blink with the corresponding direction blinking slightly brighter UNTIL the brake pedal is pressed at which time the brake lights and OPPOSITE direction signal lights up brightly. With headlights ON the running lights & brake lights don't work, turn signal causes both brake lights to blink UNTIL the brake pedal is pressed at which time ONLY the correct turn signal light blinks brightly, hazard lights work UNTIL the brake pedal is pressed at which time they turn off. You can imagine what this is like for the people behind me in traffic in Alaska in the darkest time of year. Obviously it is dangerous and illegal and unacceptable!!!

Some history of the vehicle: previous owner was a high-school age kid who overall treated the truck fairly well, but tried to install a stereo himself and blew something somewhere. I bought it (stupidly! ) in this condition. The turn signal relay clicked incessantly even when the signal wasn't in use but everything functioned correctly, even the lights. Based on the fact that the lights issue has only come up more recently I'm not necessarily inclined to think that it's even related to the stereo incident. Replacing the relay didn't take care of the clicking but replacing the turn signal switch did....but the lights are still wonky. I've also replaced the brake pedal switch thinking that maybe it was fried too since it's connected to the turn signal switch, but unfortunately this didn't fix my lighting problem either. All fuses and relays are good.

So......I think it is probably a ground issue but I'm no whiz with a multimeter & test light and need a little help/direction on troubleshooting with these tools. I can easily locate the lighting harness on the back end of the truck but I don't know if the voltages/readings are normal or not. What kinds of numbers should I be getting from each terminal for each signal (brake, turn, etc)?? What is the best way to isolate a bad ground/ground wire? Would it be best to work from the battery towards the back or from the back towards the battery? I've read about individual grounds on the tail lights.....are these easily located? Any other tools/techniques that are useful for this kind of stuff?

Really appreciate any input. Thanks in advance!

 

all the lights would normally have 12v and i agree i'd be checking the grounds which are usually located on the framerail at the back of the vehicle