I have some used parts that I'm trying to sell - one of them is an alternator from a GMC 6.2L diesel. It's a Delco-Remy alternator, looks farily new. It has one red lead marked 'Bat' - presumably for Battery. The other connector is a plug with two prongs - what is that for?!

I still have the V-belt for it so I could maybe hook it up to a drill somhow and make it spin. How would I measure the output to see if it's working?! I can post a photo if need be. I remember something about Advance Auto testing alternators - do you think they can do it outside of the vehicle?!

__________________
1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K

I think it may be for a voltage regulator

__________________
1987 560SL
85,000 miles

I though that too but the other lead is marked 'Bat' - battery?! If so, why would there be a direct connection to a battery and then a separate connection to the voltage regulator?! Maybe the battery can deal with the spikes and the instrumentation has to go through a regulator to be protected?! Would the alloy jacket be the ground on this thing?

__________________
1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K

The case is probably ground. Do a search for the alternator using some of the numbers in the casting. What year truck did it come from?

__________________
1987 560SL
85,000 miles

THe engine was a 'mutt' - block '82, some other parts '88, the alternator looks newer - don't know. Will need to search using numbers on the case.

__________________
1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K

Aren't most GM alternators of the "one wire" configuration? Maybe the second wire is for the idiot light when the alt fails.

__________________
1982 300SD " Wotan" ..On the road as of Jan 8, 2007 with Historic Tags

Found this diagram:
http://www.rowand.net/Shop/Tech/images/AlternatorWiringOverview-1973to1985Buick.jpg

I can't say I understand the diagram, but I think I should be able to measure voltage between the case (NEG) and at least the BAT terminal of the alternator when the thing spins.

__________________
1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K

Dummy light

__________________
1987 560SL
85,000 miles

Take it to a place that checks alternators free off the vehicle. To start with it is my opinion a little drill is not going to really spin it up.

Our local Autozone(and Advance, and Pep Boys) all have alternator testing machines that will spin and test an alternator outside of a running vehicle.

I'm not sure how good/accurate it is, but it'll tell you something.

-John

__________________
2009 Kia Sedona
2009 Honda Odyssey EX-L
12006 Jetta Pumpe Duse
(insert Mercedes here)

Husband, Father, sometimes friend =)

The two wire leads are for "exciter" (ignition) and the idiot light (stator).

Agreed...alternators are designed to replenish at or above idle speed of the engine...that could be around 700 rpm and up. Plus, the alternator pulley is much smaller than the crank pulley in most engines, which means it actually has to spin a lot faster.

__________________
2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

Good news - thanks.

__________________
1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K