Amp Light Staying On With One Wire Alternator Upgrade

i upgraded a long time ago and the original alternator I swapped in finally quit charging. I went to my favorite parts store and the county guy quickly found me a replacement without even punching any info into the computer lol. I installed with a new battery and wired it back up and works great but the amp light is now staying on with the key off. Any ideas? I pulled the amp light wire off the alternator and it is not on now. Did I maybe get the wrong one?

Thanks!
Todd

 

The one-wire alternator does not use the field wire that normally powers the ALT light - it's simply not connected. The ALT light depends on detecting the self-generating voltage on the field wire when you have three wires. Once the alternator starts to self-generate, the ALT light goes out because both ends of the bulb are at full voltage. I don't see how you can have an ALT light if you have a Delco set up for one wire. You have to trace it through. Somehow the field wire is a full voltage with the engine stopped, and the wire is grounding through the switch.

If I had a one-wire setup, I would just disconnect the amp light and depend on the voltmeter to report the charging state.

 

I agree with this.
That's what I did with mine.

 

What's wierd is it didn't light up with the last one. Oh well like I said I pulled the wire and all is well. Thanks guys

 

I did a 10SI conversion (GM internally regulated Delcotron) on my CJ5 and it all worked great. Later, my speedometer head blew up and I replaced it without any other change. The Alt/amp light started flickering after reassembly. Voltmeter confirms working performance. I'm thinking I got some wires crossed over or too close to the indicator light causing feedback.

 

Interesting. Might need to take a closer look at my cluster wiring.