Elecltrical Probems

[rkas48]

I have a 1981 Rabbit L 1.6 diesel. This issue just reared its ugly head.

1. When I turn the key on the radiator fan starts and will not shut off until the battery is disconnected. Turn key to start, starter will not spin or engage.

2. Place volt meter between engine block and chasis ground it reads full battery voltage.

3. Place heavy ground wire between engine block and chasis then fan stops running and engine will start and all works great until ground wire is disconnected then engine stops, fan starts.
while engine is running voltage between block and ground is .01 volt.

I have replaced both engine compartment wiring harnesses with known good ones. replaced glow plug, fan and bulb check relays and ignition switch with known good parts. I did not find any bad fuses.

I have visually, as far as possible, inspected the under dash harness and found no visible damage.

I am now lost as to where and what to check now.

Any advice and suggestions will be greatly appreciated.

[bscutt]

You should always have a heavy ground wire connecting the block to the chassis. If one is missing or has gone bad, run a new one. These cars are known for unusual grounding problems. Usually the ground wire from the battery connects to the chassis and there is a wire that goes from that chassis ground directly to the block or transmission mount. The stock wire is a heavy duty flat braid, about 3/8 wide or maybe a little bigger. 6 gauge (or two 8's in parallel) wire should suffice for a ground to the block although 4 or larger gauge is better.

[Quantum-man]

Does seem like your main earth from battery duff.
Engine and gearbox is isolated from chassis by rubber mountings.
On a Quantum, the main earth goes from battery to battery holder-floor then to a side bellhousing to engine bolt.
Without this, the current cannot flow from the fuel pump solenoid to earth. Nor starter to engine to earth...
Thus problem must lie between battery holder and engine earth, This will break from vibration on a diesel over time...
Fan on is likely linked to a relay that is being powered by a tempory rerouting of it's supply, perhaps due to the earth issue you have...

[robbertwilliams]

I had somewhat a similar problem. These cars are old enough to have had your babysitter's dad rewiring the system to his own diagram. Whoever had my car disconnected the fan from the thermoswitch in the radiator, taped the blade connectors together and called it good. So, the fan was always on...until something happened, maybe a short. I ended up abandoning the existing system and rewiring a simple separate circuit just for the fan. From battery to fuse box to thermoswitch to fan to negative. Works fine and the car doesn't overheat anymore. Check the wiring.

[Ira B]

I too would recommend making sure all of your grounds are good by cleaning all connections and replacing any crusty looking connections and wires. That alone will cure 90% of the electrical bugaboos in older VW's.