Alernator help/question

[BMSJaX]

So my truck has recently become my daily driver due to my 2000 Impala's trans going boooom , been waiting for it... the car is a piece anyways. And with the time change I now drive in the dark halfway home and I have been watching my volt gauge... Idle 14v, Idle w/electric fan 13.5v, Idle w/electric fan AND Hella H3 headlights 12v and if i sit at idle too long I slowly start droping in voltage and my lights start dimming but it i up the rpms over 1000 it goes up to 12.5v and holds. I have a standard 55amp ext/reg alt I am also running a H.E.I. dist. Does this sound like and alt problem? If so will a 65amp alt do the trick or am I gonna have to go with a 100amp alt? Money is kinda tight at the moment and the 100 amp is twice as much as the 65amp... I'd get the 100 amp no questions asked if I had the money to throw into it.

So what do you guys suggest? What alt are you running with what accessories?

[BMSJaX]

bueller... bueller... bueller... bueller...

[Captainfab]

IIRC my Suburban has a 68 amp alternator. I do run electric fans but stock halogen headlights. I haven't had any issues, but I've been thinking of upgrading to a little bigger Alternator as it seems to be marginal. Have you considered upgrading to at least a 10 or 12si Alternator? What about checking the wrecking yards for a good used one to get you by for a while?

[BMSJaX]

Originally Posted by Captainfab

IIRC my Suburban has a 68 amp alternator. I do run electric fans but stock halogen headlights. I haven't had any issues, but I've been thinking of upgrading to a little bigger Alternator as it seems to be marginal. Have you considered upgrading to at least a 10 or 12si Alternator? What about checking the wrecking yards for a good used one to get you by for a while?

Ok I found one at the local Kragen. A reman 94 amp 12si from a '84 Camaro w/305. Its more than I wanted to spend($89.99) but better safe than sorry. Gonna go get it up tomorrow.

Thank you Captainfab for your help!

[ol Curt]

Don't forget to follow some of the threads about converting from external to internal regulator.

[TheDark1]

If the problem still persists, that when you idle up the engine the volts go up, try switching the pulley to a smaller one. Some of the alternators had different size pulleys and wouldn't excite under x-amount of RPMs at the alternator. The smaller pulley would give you more alternator RPMs without changing the idle setting at the carb. Hope this helps.

[protrash64]

Be sure to get the V-belt pulley. You can have them change it at the store if it is for the serp set-up.

[BMSJaX]

Ok so i looked at the thread on wiring it in, the only problem is I have an aftermarket wiring harness and the thread and other sources say I need the resistance wire and/or warning light. I do not have either of these... Any idea as to what I need to do in order to make this work??

[TheDark1]

You can hide a warning light under the dash somewhere. I rewired mine about 20 years ago to go with an internal regulator and had the light as a resister. About a month ago I installed new Autometer gauges and just eliminated the light and have had no problems so far. I don't know why it works, but it does.

[BMSJaX]

Originally Posted by TheDark1

You can hide a warning light under the dash somewhere. I rewired mine about 20 years ago to go with an internal regulator and had the light as a resister. About a month ago I installed new Autometer gauges and just eliminated the light and have had no problems so far. I don't know why it works, but it does.

What kinda light did you use? So far I found its something with a 3 watt bulb...

[TheDark1]

Originally I just used the "generator" light that was in the dash. Now I don't have a light at all. No resistor either. I think the theory is that the light will act as a resistor when you kill the power at the ignition switch (when you turn the truck off). The light will come on and burn off the electrical signal that will back feed through the wiring harness and keep the truck from turning off. In some cases the truck will keep running if you don't have a light or a resistor. I can't explain why my truck now doesn't need one. I have an HEI ignition with a big Autometer tach. Maybe the tach acts as a resistor or the HEI needs more power to keep going than the backfeed will allow. You can use a light like in the picture. They're found under the dash of just about every GM I've seen from the 70's and 80's. Sometimes they're well hidden though. They used them as under dash lighting when the doors were open.
They have some pretty slick guys on here that maybe able to explain it better than me.