Yesterday I was in the service truck stopped, making a left hand turn and I heard the backup alarm come on. Turns out, it would come on whenever the brake pedal was depressed "and" the left turn signal was on. I noticed the marker lights were slightly pulsing opposite of the signal lights. I've heard it's caused by a "bad ground". It's easy to imagine a corroded or loose connection but how and what is being shared through ground? How are these four circuits being energized? I don't really even know how to ask the right question. Wiggled all the rear light connections- problem solved.
Sounds like two bare wires touching and one is energizing the other.
I'm just having a hard time picturing it. With turn signal, alarm, brake light and marker lights all being effected I have to check but I don't think the wiring for the alarm is anywhere near the lights.
It's the ground. The circuits share a ground bond, probably at the light. If the ground isn't being completed, the current will back-feed the other circuits with which it shares a ground bond. In a tail light, that would be markers, stop and back up. From back feeding the back up lights, the reverse alarm is getting energized and finally hitting ground. I could draw you a digram if I had more time.
That's awesome, thanks! Now to think on it a bit. Oh yeah, forgot about the backup light. Makes more sense now.
Rob Had a similar problem on one of my Freightliner shop trucks one time. I can't remember exactly what the problem was but it traced back to the ground. All the back lights had a common ground, which consisted of a 1/4" bolt through the frame. Several ground wires going to the bolt. So what happened was the one circuit was grounding through one of the lights instead of the ground, just going up the other wire instead of the ground. Turned out to just be the ring terminals were dirty, a quick clean and good to go. Remember that electricity will take the path of least resistance. In this case the bolt was rusty so the power jumped from wire to wire at the ground bolt, Not sure where it was grounding out but things were acting funny. Since everything was at the back of the truck, on the frame, the road salt and dirt had done a pretty good number on it. A few minuets with a wire brush and some emery cloth cleaning up the ground and ring terminals fixed it right up. I smeared some dielectric grease on it, but don't have much faith in it back there. Power sneaking back along a different circuit can be the bane of a mechanic's:Banghead life, chasing those little gremlins can cause you to want to blow a piece of equipment up. Those little lights on the dash that just barely glow when they are not suppose to, the one head light that is dimmer then the other, the trailer lights that don't work the way they really should. Check your grounds. hope this helps
A common issue is that separate lights will have separate grounds, if a taillight bulb with both brake and tail filaments or turn and tail have a common ground, if they lose the ground and you apply power to the brake filament say, since no ground is available locally power flows back through the tail filament and out to the rest of the taillights and possibly marker lights if they're on a common switch, until a ground is found... and lights will glow dimly because power is passing through them on it's way to wherever that other ground point might be.
I had one every time you would honk the city horn the head lights would flash it was a bad ground at the chassie
Electricity is the same as water it will find the path of least resistance a bad or missing ground is like a plugged toilet water cant flow though so it goes somewhere else you didn't want it on your bathroom floor but there it is in other words bad grounds can cause all kinds of wonky things although your lighting issue is a very common one Also its mechanics lingo for anything that you cant figure out tell the boss it must be a bad ground and they say oh must be and walk away before they have to figure it out...
Also its mechanics lingo for anything that you cant figure out tell the boss it must be a bad ground and they say oh must be and walk away before they have to figure it out...[/QUOTE] I'll have to try that one
could be cheap realty in FL.
In 1971, my Lotus Cortina had 'issues' with the turn signals. Blinked very fast. Service advisor at the Ford dealer said I needed to replace all 4 turn signals. The tech that worked on my car came out and showed me what needed fixing. He bridged a screwdriver between the turn signal housing and the bumper; everything worked like it should. Bad grounds. Fixed it by cleaning and greasing the housings in the body.
I have had bad grounds do a lot of things. One machine would crank the starter when the key was just in the on position. Wouldn't stop either. One kicked on of my guys butt good. spent a day pulling a computer out of another machine only to find three bad ground wires.