2004 C70 Transmission jolts, MVSOLVED bad ground

[abscate]

Just pulling your leg, Mike...

I can't keep current with all these potentials...

[justinwerner]

Still fighting this problem... Cleaning the grounds as I see them. Can anyone please provide a better explanation for the location of grounds 31/91 31/94 31/7. I've looked as best I can without taking apart too much, but picture would save me tons of time and frustration. I've looked at the wiring diagrams but still cant find the matching position on the car. Any help you can provide would be appreciated. Tks.

[Herb Goltz]

I would measure voltages at the alternator, at the battery terminals, and over the B+ cable that goes to the fuse box, as well as the negative cable. High resistance in corroded cables is well established in these cars.

Good luck!

[regent]

If you've got an IR remote temperature gun at hand or you could borrow one, you may scan all suspect points and find the offender(s) sooner that way, and then use the VOM to confirm there's a drop in voltage right there.
When you do, you want to put some electrical load on a running engine - similar to the conditions in which you've been having 'the jolt'
See if this helps you locate the missing grounds/Earths/Marses (whichever planet's name you wann'a call them )

[justinswerner]

Putting a voltmeter to the negative side of the battery and to the casing of the alternator showed .56 which is pretty high resistance on negative side. I was told it should be less than .10 I cleaned off 31/15 ground and it dropped to .36, so I'm heading in the right direction. I was hoping to clean them all and see how far that got me.
The battery is brand new. Readings from off are 12.6 and only 12.75 with the car running. The voltage regulator was replaced, and I think bench tested when it was out and was found to be charging OK. I have not had any hard starts or drained battery issues, so the low reading direct to the negative side resistance. Everyone seems to think the issue is on the ground side, so I'm trying to make sure I've eliminated that first. I just cant seem to find a few of the grounds.

[justinswerner]

Not to celebrate too early, but I think I found the bad ground. 31/55. What a pain to get to, but was able to back it off mostly, wire brush and degrease/spray out what I could. Put it all back together and I could not replicate the problem even using every electrical component at the same time. The best test was checking for voltage drop increased resistance test that confirmed the issue was with the negative side. My results started with .56 and dropped to .01. I still never found 31/15, and need to still get to 31/4. I still get a little dimming of the dash lights when I use a heavy draw component, but it's nothing like I was getting before. Thank you all for your help.

[abscate]

Well done....both to you and the advisees here who pointed you to grounds/earths

That would be mike of course....

[rmmagow]

These grounds, what exactly do they look like? Wire with a ring bolted to the body? Is it that simple or are they somehow encased so they are difficult to pick out?

[regent]

Most of'em are are ring-terminated and pretty much 'hidden in plain sight' but not that hard to get to (see illustrated locations on the attachment).

As you can see, the symbol is a "T" walking upside down, which gives us sufficient grounds to suspect it was first introduced in Australia

[precopster]

And my first instinct on this one was actually to check that the rear wimdscreen is clean. Lucky I didn't go for that solution first