Question, turn signals and brake lights work except when headlights are turned on. The right side break light works when applying the break and both signals still work, but with the headlights on and applying the break the entire passenger side goes out or doesn't work. Any thoughts? I already replaced the bulb so this has me a bit baffled.

 

Electricity can do a lot of confusing things, first thing you need is a wiring diagram for your car then you need to understand what your looking at if you have those two things you should be able to track down your gremlins by understanding what is common.

I know not much help.

 

To expand on what I was saying when you understand the wiring diagram and think you know what is wrong disconnect it, test for grounds and shorts until you find the problem.

 

Repost of a repost, but ponder this:

Here's the response, I just posted on another electrical thread below

My 0.02 worth. If you're gonna start messing with electrical problems on a C3 in a serious way, you need to arm yourself with the knowledge, documentation and tools to find and fix your problem. Otherwise, you're better off, taking it to a professional, because these things can get complicated (I'm an ex-Electronics Technician).

First, you should have the GM Service Manual, then I highly recommend the laminated color, wire diagram from any number of sources. It's big, it's sturdy and all the wires are in the same color as the car.

Finally, I highly recommend having a tool called the Power Probe. The Power Probe III is an amazing tool, that can put power (or ground) to any part of the vehicle, it will tell you instantly, whether there is a circuit or not (touch the connection and the green light goes on automatically, to tell you, that yes, there's a complete circuit). And with the Power Probe, you just keep going back from the tail lights for example, until you find where the power was interrupted. With the Power Probe, you can apply 12v with the rocker switch to the tail light wires anywhere in the circuit and watch them come on (or not). I would't touch a car's electrical system, without it. At $100 or so, it's not that expensive, versus the hours you spend, bumping your car with your fist and visually examining it (and getting no where), because your personal time is worth something and this will save you a lot of time!

 

FACT>>>>PLAIN AND SIMPLE.....you have a BAD GROUND (lack of a ground) on the side that is giving you a problem.

BECAUSE...if when you turn on your park lights/headlights....and ALL of your lights come on as designed. AND...when the headlights are OFF...and the brake and turn signal lights ALL work (front and rear)....BUT...when you turn on your headlights the rear lights do not work correctly....then IT IS A GROUND ISSUE.

IF...you have the same issue in the front where the turn signals DO NOT work when the headlights are ON...it is the SAME thing....a BAD ground to the light socket/bulb.

DUB