CS121 harness

[elf w/capital T]

hello! I converted to a serpentine setup a while ago... got a brand new replacement CS121 alt. ( P-L-F-S) on harness. the harness I took off the old one (from junkyard) just has the brown wire ( *F* position) and nothing else in the harness.

I plan on installing the AAW Classic Updates kit and my question is.... do I NEED the original wiring P-L-S as well? I know I can buy the new harness... but isn't the brown just for a light or something? (not sure where on the cluster it would be)


Electrical is not my strong point and I have done some research and found that my new alt ISNT the cs130 I thought I got and everyone elses harness have a fat red, two browns and a grey wires.....

any help would be greatly appreciated.

[starterman99]

what did this alternator come off of ? or what is the delco number stamped in the case. If we can id the alternator then hooking it up should not be a problem.

[elf w/capital T]

Came off a 95 c1500 2wd 5.7L.... lol I looked up all the stuff for a cs130.... and I might just leave the original harness (brown wire only) hook that up to the light spot on the cluster... but as far as the big red wire where normally people just route it to the POS Wire going to the battery. ... that's what I'm concerned about...I would rather not burn up the new alt....

[starterman99]

you wont burn up the alternator if the red wire from the S terminal on regulator is not hooked up. GM produced thousands of trucks using only the light terminal in the regulator to activate the alternator and provide for indicator light function.

[VetteVet]

You won't need any wires but the brown one going to the alternator from the key switch or the charging light depending on which dash cluster you have. The brown wire is the same one that goes to the external voltage regulator on the stock trucks. It will go to the L terminal on the alternator. The only thing you will have to do is increase the resistor value from 10 ohms on the stock truck to 35 plus ohms on the brown wire to the L terminal. Painless wiring recommends an 85 ohm 5 watt. I have heard that using up to 300 ohms .5 watt works. Using high resistance inhibits the regulator and affects the charging output so don't go over that.
See the diagram.



The CS 121 is the same as the 130 except for the diameter 121mm
I assume you have a 67 to 72 truck.

[elf w/capital T]

Starterman and vette you guys are awesome. Thank you so much.