First off, I've read plenty on this and realize there's a million threads regarding the swap. Sorry for adding another but I need some clarification.

Got the trail gear mounting brackets and the alternator and harness from this thread
https://www.yotatech.com/forums/f131...thread-284572/

The alternator mounted up ok and spins normally when the truck is running. For the harness, I wired it like his write up also. From toyota harness: yellow to lamp pin, red to ignition pin, and white to the sense pin. My question is regarding the other white, the larger one that was previously used on the alternator output stud.

Do i wire it in with the sense wire and leave the side by the battery attached where it was stock (the alternator fuse)? I've left this white wire out as I replaced it with a 4awg charge wire and thought that made it obsolete. The brake and charge lights are on. Getting 12.3v at the battery.

Thanks, not sure why but having a tough time nailing this down.

 

Is it possible your GM alternator is not putting out like it should ??

Measure the output at the alternator??

A poor solder joint?? A

Any other poor connections??

Where did you get your alternator New / rebuilt or used ??

 

Thanks for the reply, pulling my hair out over here.

Alternator is new from Oreilly's

Output at alternator is same as battery, 12.5v

Just rechecked connections and they seem to be in good shape

I just put the original alternator output wire in with the sense wire and there was no change. When testing the GM harness that plugs into the alternator I get 12v constant on the sense wire, switched 12v on ignition wire and no voltage on lamp wire. I've also tried increasing engine speed and had no change in voltage. Alternator case shows continuity with ground.

 

Wouldn't surprise me if you got a bad alt. I got one from Advance with a lifetime and have to swap it out about every year.

 

Ding ding ding!!

That's exactly what it was, thanks muddpigg. Bad out of the box. Went back and it failed a test. I thought it had to be with the wiring because I was doing the swap and didn't suspect the alternator at all. They tried giving me a new one and I just got a refund, no thanks. Read on some different forums and a guy said he got five bad ultima alternators in a row. Apparently they just send them to Mexico to be refurbished and they replace whatever part failed and ignore the rest. Stay away!

While you guys are here. I'm going to go to the chevy dealership to replace it. I saw a list of alternators that will be compatible but can't find it. Anyone have it handy?

 

Cross reference a '90 caprice 5.0. Should have up to 120 amp (haven't found that one) think mine is 95 amp. Has v-belt. Post up what you get and price. I was thinking a power master.

 

Cool, thanks

 

That is the problem with rebuilt parts the quality has gone way downhill.

Better luck with the next alternator.

 

I ordered a 100 amp alternator from gmpartsnow.com for $160. Hopefully will have the peace of mind of a new alternator now.