Finding/Diagnosing ground wires? - PeachParts Mercedes-Benz Forum

zippyclown · #1 12-19-2012, 01:32 PM

Guys, I have an '81 300D and am by no means a mechanical or electrical wiz, so I turn to you all. Can somebody tell me simply how to find and diagnose ground wires? Seems like when it's wet out (or just a coincidence) my dashboard lights go out. At times my rear right tail light goes out. Then it'll all come back on days or weeks later, seemingly when it's dry again. Mostly concerned about my tail light for obvious reasons. Bulb is fine and other lights in the same housing all work. The fact that some of these lights are going out and coming back on makes me think ground wire or wires. How do I find and fix this? And how do I find a ground wire for, say, the dashboard lights?

Would a mechanic even bother trying to fix this for me if I decided to put the problem in his hands? Or are these electrical gremlins something they usually don't want to touch?

Thanks again. Don't wanna get pulled over.

vstech · #2 12-19-2012, 01:46 PM

since all the lights in each light assembly get ground from the same wire, I'd vote on it being the socket.

as for the IC... it gets ground from the large cluster connector. and it transmits the ground to the gauges through the metal strips on the back of them.

zippyclown · #3 12-19-2012, 01:49 PM

Quote:

Originally Posted by vstech

since all the lights in each light assembly get ground from the same wire, I'd vote on it being the socket.

as for the IC... it gets ground from the large cluster connector. and it transmits the ground to the gauges through the metal strips on the back of them.

vstech, what would be the recommended course of action here? Much appreciated.

zc

Simpler=Better · #4 12-19-2012, 01:58 PM

Pull up your plastic panels in the trunk, the grounds are hidden under them.

MB ground wires are brown-this should help you out.

zippyclown · #5 12-19-2012, 02:49 PM

Quote:

Originally Posted by Simpler=Better

Pull up your plastic panels in the trunk, the grounds are hidden under them.

MB ground wires are brown-this should help you out.

Thanks for the info!

ah-kay · #6 12-19-2012, 03:12 PM

I think the 'ground wire' issue is overblown. The only ground issue I had in my car experience was the ground wire to chassis, at the engine or tranny. It gave intermittent no start as it was not bolted on properly by the PO.

It could be a lot of issues with intermittent electrical issues. Could be the connector, socket, light socket, bad electronic modules, dry solder joints etc. Your tail light problem could be a corroded light socket. The other most common problem is the car had an accident, fixed but some wires are pinched - it would be impossible to fix unless it gives a hard short. In closing, it is PITA to fix intermittent electrical problem until it becomes a hard short. You have to be patient and do a divide and conquer, removing some electrical parts to narrow down the area.

Good luck.

whunter · #7 12-19-2012, 03:50 PM

Quote:

Originally Posted by zippyclown

Guys, I have an '81 300D and am by no means a mechanical or electrical wiz, so I turn to you all. Can somebody tell me simply how to find and diagnose ground wires? Seems like when it's wet out (or just a coincidence) my dashboard lights go out. At times my rear right tail light goes out. Then it'll all come back on days or weeks later, seemingly when it's dry again. Mostly concerned about my tail light for obvious reasons. Bulb is fine and other lights in the same housing all work. The fact that some of these lights are going out and coming back on makes me think ground wire or wires. How do I find and fix this? And how do I find a ground wire for, say, the dashboard lights?

Would a mechanic even bother trying to fix this for me if I decided to put the problem in his hands? Or are these electrical gremlins something they usually don't want to touch?

Thanks again. Don't wanna get pulled over.

This sounds like more than one issue.

http://www.peachparts.com/shopforum/general-information/296474-w123-instrument-cluster-printed-circuit-board-repair.html

http://www.peachparts.com/shopforum/diy-links-parts-category/188540-instrument-cluster-odometer-speedometer-tachometer-links.html

.

zippyclown · #8 12-20-2012, 02:16 PM

Quote:

Originally Posted by ah-kay

I think the 'ground wire' issue is overblown. The only ground issue I had in my car experience was the ground wire to chassis, at the engine or tranny. It gave intermittent no start as it was not bolted on properly by the PO.

It could be a lot of issues with intermittent electrical issues. Could be the connector, socket, light socket, bad electronic modules, dry solder joints etc. Your tail light problem could be a corroded light socket. The other most common problem is the car had an accident, fixed but some wires are pinched - it would be impossible to fix unless it gives a hard short. In closing, it is PITA to fix intermittent electrical problem until it becomes a hard short. You have to be patient and do a divide and conquer, removing some electrical parts to narrow down the area.

Good luck.

Something a local mechanic would typically be up for?

ah-kay · #9 12-20-2012, 02:25 PM

Quote:

Originally Posted by zippyclown

Something a local mechanic would typically be up for?

I really do not know. I am an engineering by training so I do my own debugging. I can figure it out. A shop specializes in auto electric may help. You need to have the car's wiring diagram which shows the color code of wires and the distribution.

You can always ask and limit your diagnostic charges.

zippyclown · #10 12-20-2012, 02:35 PM

Quote:

Originally Posted by ah-kay

I really do not know. I am an engineering by training so I do my own debugging. I can figure it out. A shop specializes in auto electric may help. You need to have the car's wiring diagram which shows the color code of wires and the distribution.

You can always ask and limit your diagnostic charges.

Ok. Well I'll start by checking the socket and work back as far as I'm comfortable. Maybe I'll find something. Seems like most of my problems were easier fixes than I originally thought. The car hasn't had a very tough life.