Help! Electrical Gremlin in my 2003 Jetta wagon

Tdimrtwo

Veteran Member
Joined
Aug 29, 2018
Location
North Texas
TDI
03 Jetta wagon, 15 GSW, 02 Beetle
For about a year, I’ve had an intermittent fault that happens randomly, but maybe averages once every other month. The turn signals and headlights quit working, and the wipers won’t shut off, but also run very slowly and might get stuck halfway up. Several unrelated things acting up simultaneously, sounds like a bad shared ground right? Last electrical thing I did was to install a new “european” style headlight, which required me to rewire the connector to match the headlight. So, I unplugged the headlight wiring harness upstream of my wiring changes, but no change, the problem still existed. Got out my Bently manual wiring diagrams, and traced the wipers back to a ground connection under the battery tray. Unbolted the nut, it didn’t really look bad, but I cleaned it anyways, and boom, the problem went away. Ok, my work is done, I Might have to clean it again in another ten years, but I can live with that. Then a few weeks later, it happened again. Pulled out the battery tray, thoroughly cleaned the connection from the battery and the one going to the rest of the car and added a jumper wire between the two ground studs in case there was a bad connection going into the car body. Problem went away, but only for a few weeks. Yesterday, on the way to Arkansas, it happened again. Removed my ground jumper, cleaned everything thoroughly, even the ground going to the transmission bolt, and now it’s working again. But I don’t think I’ve found the real problem, and I think it’s likely to happen again. Anyone seen this before? I’m an arrogant, overconfident electrical engineer, and this is a simple 12 V Dc circuit, but i admit its got me totally flummoxed.
 

Matt-98AHU

Loose Nut Behind the Wheel Vendor
Joined
Apr 23, 2006
Location
Gresham, OR
TDI
2001 Golf TDI, 2005 Passat wagon, 2004 Touareg V10.
The load reduction relay powers all the items you mention... that might be the common source to check.

Relay with a big "100" printed on the top of it in position 2 on the very lower part of the relay panel under the dash.
 

Tdimrtwo

Veteran Member
Joined
Aug 29, 2018
Location
North Texas
TDI
03 Jetta wagon, 15 GSW, 02 Beetle
Found it!!! I Had the battery out, powering up the car with jumper cables, and the problem went away. But it came back as soon as I bolted down the battery tray, so the problem has to be under the battery. I pulled back the harness and saw a third ground connection way up under the fender. Got a socket on it and felt no resistance, it was only finger tight. Connections were corroded and bolt was rusted. Cleaned everything up and it works perfectly now. Nothing like being stuck 6 hours from home to motivate you to keep looking until you find the problem.
 

irvingj

Veteran Member
Joined
Nov 28, 2006
Location
Etna,NH
TDI
2005 Jetta Wagon TDI (PD/BEW)
I was having some slow crank/hard start issues and read about "the ground under the battery." After removing battery, I found THREE grounds under there. Cleaned 'em all. Also replaced both positive and negative battery cables, due to corrosion under the insulation on the ends; you might want to check those too. (Result: In my case, the problem didn't finally go away until I put in a new battery... but was probably a combination of issues.)
 

Tdimrtwo

Veteran Member
Joined
Aug 29, 2018
Location
North Texas
TDI
03 Jetta wagon, 15 GSW, 02 Beetle
Thanks, I’m quite sure the loose, corroded third ground connection under the battery was the root cause, and that it’s now totally fixed. The problem had progressed from intermittent to continuos while I was in Arkansas, and disappeared completely after I cleaned and tightened it. Drove it home with no issues at all. It only took me a year to found and fix the problem.
 

Rrusse11

Veteran Member
Joined
Jan 23, 2014
Location
PA Deutsch Country
TDI
2002 Golf, 5spd; 05 Jeep CRD
Congrats! Just the incentive I need to actually take my battery out and clean all 3, my wipers
have been flaky for a while. Coupled with some very occassional weirdness with my sunroof.
 

irvingj

Veteran Member
Joined
Nov 28, 2006
Location
Etna,NH
TDI
2005 Jetta Wagon TDI (PD/BEW)
Ha-ha... that's definitely my OCD kicking in! I also make a note in the owner's manual/logbook.

Been doing that for years on my cars, motorcycles, boat, house repairs, etc. Comes in handy to see when X was last done or some device was installed/replaced, also useful for troubleshooting problems down the road. Used to make drawings, these days I document with a digital camera.
 
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