10v on my ground wire.. where do I start to diagnose? (1 Viewer)

[iliketomakestuff]

I've been having electrical issues on different parts of my 76 FJ40 over the last year or two and have been replacing wires etc.
Today, I tested voltage between my (-) terminal and the block, while the engine was running, and I got around 10v :/

So.. as someone without much auto/electrical history, how do I go about diagnosing the issue? I assume pulling fuses one by one to at least isolate the circuit causing the problem? I tested removing every fuse in sequence while it was running, and while the 10v did drop a little at a time down to 5v, it never went away, even with NO fuses in the block.

Any other help would be greatly appreciated!

 

[charliemeyer007]

I would start with pulling apart and cleaning every electrical connector you can. That green corrosion stuff can cause stray currents. Make several blown up copies (A4 size or bigger) of your wiring diagram(s), use one as your working unit. Make corrections and notes as you go. When you are done, copy over the good stuff to the spare one and then have it laminated. Before laminating it, on the back write down all your tune up specs, torque setting, part numbers, fluid types and capacity and things like that for easy reference.

 

[iliketomakestuff]

I would start with pulling apart and cleaning every electrical connector you can. That green corrosion stuff can cause stray currents. Make several blown up copies (A4 size or bigger) of your wiring diagram(s), use one as your working unit. Make corrections and notes as you go. When you are done, copy over the good stuff to the spare one and then have it laminated. Before laminating it, on the back write down all your tune up specs, torque setting, part numbers, fluid types and capacity and things like that for easy reference.

Great idea

 

[Malleus]

You have a problem. The negative battery terminal and the block should be connected, meaning they should be two branches of the same ground circuit. You should not have a voltage between two grounds, if you do something is wired incorrectly. It would be the same as seeing a voltage between opposite side of the block, or from one fender to the other.

Try disconnecting the alternator.

 

[Rocky_LC]

You must have bad grounding between the negative terminal and the block.

Clean up all the heavy connections between the block, chassis and negative battery terminal, including cleaning up the terminal connection.

Don’t disconnect your alternator….

Rocky

 

[iliketomakestuff]

It seems to have gone away. Must have been something in a connection. After cleaning and reattaching it’s all good. Thanks everyone!!!

 

[diesellibrarian]

Voltage at a ground = resistance = bad ground. 95% of electrical problems I've ever encountered on a car are because of resistance caused by bad grounds.