I have been saddled with the un-envionable task of working on a Dodge truck thats been converted to a Delco 21SI Alternator.

The original alternator went bad and the new one only slightly charges. I am thinking there is something wrong with the remote sense wiring.

I have looked on the net and really cant find how this alternator is supposed to be wired. I got a sneaky suspicion that it was installed incorrectly and subsequently ruined the alternator.

Alternator has:

BAT connection
Ground cable
2 wire typical GM plug ( I am assuming this is the sense wiring)
And a small purple wire mounted on stud between the BAT and the two wire plug. ( I am assuming this is the excite wire)

HOW can I jump this into full field mode?

Anyone help with where the wires should lead to? THe bat is obvious, but the 2 wire plug and the purple wire have me at a bit of a loss.

Shouldve told him to just run the self excited 21SI one wire alternator andbe done with it.

I don't like these so called "one wire" lashups.

Sometimes, though, the guys who made it is the place to go:

http://www.delcoremy.com/pdfs/service_manuals/legacy/1G-286.pdf



http://www.delcoremy.com/Manuals.aspx

I hate one wires...but that being said....Since you said it is a conventional 2 terminal regulator there are 3 versions of the 21...One with 2 terminals,One with 4 terminal and one with no normal "GM" plug and just studs on the rear.
The small stud (10-24) you should see is just towards the outside and slightly to the left if viewed from the back of the case from the main output stud and should have a "R" cast in the case next to it (i`ve seen some that don`t) this is a "relay" terminal and while it has some various uses...normally it is a tach output for diesel engines.
The regulator plug is normal GM stuff...looking at the back..left terminal is number 1 and is the Ignition/idiot light (I), the right one is number 2 and is the external voltage sense (S)

The thing that confuses me a little is you saying that the stud is in between the output and the regulator plug...the one version of the 21 with no regulator plug and 2 10-24 studs on it has a stud in that location and would be the "I" terminal...I`m wondering if someone has changed to a normal plug style regulator at some point in it`s life.

Hope that helps

Rick

440SixPack, thanks I printed that out it will help. Funny it never came up in my numerous searches.

BLown71X, yes, the other wire is for the tach drive on the diesel engine as you stated (at least it appears to be to me). Alternator is on a Cat engine, and would have had a tach on its OEM application.

Assuming S should have battery voltage, just at a remote location, I will check to make certain I have voltage there. The I terminal would seem then it has no function on alternator operation, same for the tach output.

SO, assuming I have voltage at S and voltage at Batt, if I am not charging still, with the new alternator, it would be reasonable to assume the new alternator is bad.

Gonna go back out to the field and check the voltages again.

Thanks for the help guys.

Doc.

Turned out to be a ground problem.

Seems this guy has somehow grafted a Dodge Ram Cab onto a GMC Topkick frame. Took me a bit to figure out what the truck actually was.