hey guys, so along with the turn signals not working, pain in the butt, my headlights/ brake lights/ and dash lights all strobe. these lights all work fine when in neutral or park but as soon as I put the truck in gear its impossible to drive at night. its a 74 k10 and I have a new battery, new alternator, the power cable from battery to starter was rubbed through so I replaced that too. Other then that I went through and cleaned/ sanded down every ground I could find under the hood to insure a good connection there. not sure where to go from here and any ideas would be better then a new wiring harness lol.
The big questions are: Why is it that this only happens when the transmission is shifted into gear and not in P or N? And why do they strobe on and off rather than dim down and stay that way?
If you have found a definite/consistent connection between the lighting issue and the transmission being put in gear, maybe that is what you should think about. I'm sure that, given the vintage of the truck, there are no electric controls associated with the transmission. There might be a kickdown switch on the gas pedal but that shouldn't effect the lighting.
I'd start by using your VOM to determine if the lights are flashing due to a fluctuation in power supply rather than a grounding issue. I can't imagine how a ground path (all of them) could somehow be made/broken in a cyclic manner. That definitely sounds more like a voltage supply problem.
Unlike later model trucks, your entire electrical system is fed by one main feed from the battery. Once inside the cab, it is branched off to both BAT terminals in the ignition switch, the fuse block, the horn relay and the headlight switch. But, other than lighting, you haven't noted any other electrical stuff acting up. IDK?
An easy first check would be at the firewall junction block. While you are in that area, check the fusible links. Next check is at the main firewall connector. Then under the dash at the splice point.
One other thing, does the engine have to be running for this to happen - or does it also happen if you turn your lights on and shift out of P/N with the engine off?
Reason I ask; If it happens with the engine off, it will be a lot easier to check voltages down the line. If not you will need an assistant to apply the brakes or a very reliable e-brake.
What if you disconnected the shifter linkage at the transmission and seeing if it still happens.
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