Any idea why previous owner did this?

[CTaylor]

There is a wire that goes from one of the outter case studs on the alternator and is attached to one of the screws that holds the voltage regulator to the firewall. I figure it’s a added ground wire? If so why? And what purpose would it serve?

 

[TMyers]

It appears to be a ground from what I can see. Maybe that box on the firewall wasn't grounded. Who knows? Maybe he found a piece of wire with ends already on it.

 

[DVolk]

I have added extra grounds on several vehicles before ,I'd leave it their but re run out to look better if you like

 

[Tuesdak]

The prior owner may have done this due to bad grounds between the cab and engine. That wire can be a ground loop: a bad thing. Cut it short from the regulator and ground it to the firewall or take it off completely. The best way to add grounds is a battery cable sized strap from the engine to the frame and engine to body.

If you run the frame and body straps to the negative terminal of the battery (never do this) consider what happens if the battery to engine cable fails or gets high resistance: hit the 10HP starter asking 800+ CCA. The current isn't going through the failed battery to engine cable so it goes through the body and frame straps from the battery, but, it still has to get to the starter on the engine so it arc welds bearings, burns up small ground wires, or catches them on fire on the way from the body/frame to the engine. If you properly ground engine to body and engine to frame the negative battery cable failing stops everything.


One other thing: ground things away from the electrically noisy alternator. Also don't double duty existing ground locations with the ground straps. Put the grounds elsewhere on their own bolt. If you don't the ground wires become antennas and the radio can pickup noise that is normally dissipated into the larger ground body. ECM's are also affected by putting other grounds on theirs.

 

[B.G. Smith]

That dooma fitch on the firewall is an old style alternator regulator (pre ecu). The alternator must have quit. bg

 

[dodgenstein]

91's were the last year to have external regulators from the factory.

 

[CTaylor]

91's were the last year to have external regulators from the factory.

so that regulator would be correct for a 91.5 then? My early 91 also has one.

 

[CTaylor]

The prior owner may have done this due to bad grounds between the cab and engine. That wire can be a ground loop: a bad thing. Cut it short from the regulator and ground it to the firewall or take it off completely. The best way to add grounds is a battery cable sized strap from the engine to the frame and engine to body.

If you run the frame and body straps to the negative terminal of the battery (never do this) consider what happens if the battery to engine cable fails or gets high resistance: hit the 10HP starter asking 800+ CCA. The current isn't going through the failed battery to engine cable so it goes through the body and frame straps from the battery, but, it still has to get to the starter on the engine so it arc welds bearings, burns up small ground wires, or catches them on fire on the way from the body/frame to the engine. If you properly ground engine to body and engine to frame the negative battery cable failing stops everything.


One other thing: ground things away from the electrically noisy alternator. Also don't double duty existing ground locations with the ground straps. Put the grounds elsewhere on their own bolt. If you don't the ground wires become antennas and the radio can pickup noise that is normally dissipated into the larger ground body. ECM's are also affected by putting other grounds on theirs.

Good information as I do suck at electrical. I will remove the wire and see if the volt meter starts bouncing if it does I presume its safe to cut the wire close to regulator and attach it to a cleaned off part of the firewall as you say?

 

[dodgenstein]

Yes, correct for all 91 and 91.5. ECU regulators came in 1992.

 

[ENafziger]

Grounding the voltage regulator is a good thing, and some would even say that doing it will help extend its life indefinitely. However, it is best to run the ground directly to the negative terminal on the battery. And make sure you scrape off the paint or clear coating on the regulator to ensure a good ground.

 

[Tuesdak]

Good information as I do suck at electrical. I will remove the wire and see if the volt meter starts bouncing if it does I presume its safe to cut the wire close to regulator and attach it to a cleaned off part of the firewall as you say?

I would ground it by the regulator on the firewall. Then take a new battery cable from the parts store and run a strap from the firewall to the engine. That strap will "fix" whatever ground issue there may have been. The little wire is too small to handle all the current from the body to the engine.