alternator or lights

[goalvanny]

so iwas getting the truck ready to wheel in the pines and ran into problems.the alternator went bad and i put in a factory 63 amp one. with the wipers and electric fan it works fine but when you put the lights on it only last for a few seconds ten drops to 12 volts ok so i tried the lights only and had the same problem. belt is not slipping so i know thats not it. just wondering what you guys think.

i rewired the truck when i had a fire in it a while but never had problems till now. do i have to hook up both spade terminals on the alt or not i only have the one hooked up. and what is the cheapest easiest swap for an alt like in the 90 ir 100 thanks sorry for alll the questions

o and alll the lights are factory and i dont even have a dash so thats not a problem either

 

[toomany]

Did your lights pull the voltage down that much before the fire? What about before the alt swap? I've got a stock amprage one, and I can run the lights, heater, wipers and then if the fan comes on, the voltage will drop down to 12. At idle I can only run the heater and lights before the voltage drops.

When using only one of the terminals, I believe you have to have it hooked to the lower one. And the alt will only charge once it hits a certain RPM. Some will continue to charge if they drop below that RPM though.

I'd check the wiring for a short. And make sure the grounds are good too.

 

[goalvanny]

after the fire it was fine but this is the first time having it out at night so it was the first time actually using the lights not just checking to see if they work and as far as idle charging it is fine with everything but the lights i just dont see the lights pulling more amperage then the fan and wipers together.... all the lights are factory so thats what confuses me... i am gonna check my grounds when i get a chance and a short maybe but i would think my fuse would pop if the short was that bad to suck the alt down like that

 

[dremu]

I suspect that some of your wiring -- more likely a ground cable, but maybe the positive side -- is corroded or has a crappy connection.

The opposite of a short, actually, is an open or partially open (i.e. resistive) connection ... which will drop some voltage due to the resistance.

It depends on where you were measuring the 10V; if it's at the battery, check the connections to the alternator and the grounding from the block to the battery.

If it's at the lights, check the wiring to the lights -- including the grounds. See a pattern here?

If it's at the alternator, from the terminal on the back to the case, you either have a bad or miswired alternator, or the grounds are whacked somewhere.

-- A