1998 Venture, 214,000 miles -Great vehicle.
Crazy electrical thing going on almost a year; When Headlights are ON, and Left Turn Signal is turned ON, the four bulbs and five filiments in the Rear Left housing all begin to flicker in a random sequence creating an unmistakable turn signal, and cute light show, but not in the opinion of a local cop who stopped my wife this week. I’ve checked lamps and visibile wiring, jiggled it during operation and no change. Is there a chip that controls these processes that may be fickle? If so, where is it and is that a difficult or expensive fix? Many thanks.
One cause might be a dual filament bulb on the left side where one filament sags and makes contact with the other filament. Start by replacing the bulbs including the front turning signal/parking light bulb on the left front side and the stop/taillight bulb and the left rear side.
The problem could be the multi-function switch (the one on the steering column that handles the headlights, turn signals, and possibly other things). Lots of circuits go through that switch and they can cause all sorts of strange electrical problems when they wear out.
Truly wierd electrical anamolies are usually caused by faulty electrical grounds. I think your problem is wierd enough to qualify.
Carefully check the ground for the lights on that corner of the car. Try running another ground from the batttery to the ground on the lamp.
I agree with what JayWB stated. If the grounding proves to be ok then check to see if you are getting the proper voltage to the lights. There may be a bad connection to them.