1984 long bed 22R carburated...

I'm getting a strange variation when I measure battery voltage using different ground points. I use the battery positive for the red cable from my DVM. For the black cable, if I use the neg battery terminal I read 12.3v. If I use the battery cable where it bolts to the passenger side engine compartment wall, I get 12.3v. But if I use a fender bolt on the driver's side engine compartment wall, the reading is 10.9v. If I use a bolt head screwed into the engine itself, the reading drops to 8.8v . Same low number if I clip the neg DMV cable to a metal brake line.

There may be a ground strap from the engine or trans to the chassis that has a bad connection (is there one on this car?), but I don't know why I'm getting a voltage drop from one side of the engine compartment to the other side. Both bolts are tight. Is there something I need to know about this truck?

John

Steel is not the best conductor of electricity under the best of conditions. Add a bit of rust/corrosion at connector points & it can be downright unreliable.

You are on the right track, when you encounter a voltage drop, take every connection apart between the "good" voltage & the "low" & clean them & test again. It's not rocket science, just trace it out one connection at a time. Sure it's a PITA, that's why the pros get so much for doing it...

Dave

Instead of the batt neg cable to the fender I put a longer cable to the intake and from there to the chassis. I had been troubleshooting a no crank problem. 22re 1985

IIRC, there is a ground wire on the backside of the passenger fender that runs from the passenger fender ground bolt down to the frame, where as there isn't one on the drivers side, this is likely why the voltage drops., and is why when adding accessories grounding them to the body usually ends up w/them not working, or not working correctly.

You could have a engine to body/frame strap that isn't connected, from past engine work, or you could have a degraded ground wire in a harness somewhere, this happened to me. If you can't find one on the drivers side fender, you can simply add one. Run it up from the frame to the coil ground(on the drivers fender), this should give you the same 12.3 volts on a bolt on the drivers fender as it does n the passengers.

I would start with cleaning the terminals, the ground strap ends, and check that all of the ground straps are attached, then add additional straps.

Thanks for all the tips everyone...I've had a lot of strange voltage drops in this car for the two years I've owned it and it's time to start correcting them. For example, I turn on the halogen interior light and the voltmeter drops from 12.5v to 10.8v, sometimes but not always. Same with the parking lights, same with the brake lights...always sometimes but not always.

When I connect a ground to the frame, am I going to have to tap and drill a hole or are there some natural points up front for this.

Check the main cab ground point as well, all the light grounds go through it. Location: driver's side kick panel.

Should be a threaded hole for the factory ground strap on the passenger side. On my '85 there is the battery ground to the fender. Then from there to a bolt on the frame and from there up to a bolt on the side of the motor mount bracket on the engine. Also back of the head to the firewall. I upgraded all the ground connections with some 1/0 welding cable on my '85.

Here's one problem fixed: I was using a remote starter to turn over engine (no start problem) and saw large sparks coming from the battery ground strap connection at the engine compartment wall. I had checked that connection before and it seemed tight. I checked again with a 10mm socket/rachet and found I could tighten it a couple of turns more.

After that most weird voltage readings changed. Now when I turn on interior halogen lamp voltage drops from 12.7 to 12.6v instead of 12.7 to 10.9v. Same with parking lights, same with pressing on brake pedal. What a difference a ground makes!

One last weird problem. Temp gauge reads real low with old temp sender, with new temp sender it reads very high. Measuring resistance at temp sender (which depends on coolant temperature) the reading varies greatly depending on which ground point I use. I'm hoping a good engine ground will fix this problem.

What's the best size wire to use for chassis and engine grounds. If I don't have welding cable, will a 12 gauge wire be good enough, or is 10 guage necessary (or larger?).

The bigger the better. You can get the braided ground straps at most auto parts stores. Those work very well. And don't just look at a connection or tighten with a wrench. Actually take it apart, wire brush all the terminals and even use a little sand paper to clean up the metal around the bolt hole then put all the terminals back. And at the same time, you can check the ends of the wires for corrosion. They will often feel different than the rest of the cable, either very stiff or very flexible. You often get corrosion up under the insulation.

If you don't factory threaded holes in to use, or have access to a welder, drill and tap or drill and use a rivet, or you could use a self tapping bolt. It doesn't have to be a large bolt, I used a 1/8" screw a few years back and it worked fine until I had to add a few more ground wires to it, then I just welded a bolt to the frame.