[barnym17]

Do you have a base hobby shop? Or barring that a motorpool close by? The offer of a cold one will bring an old guy running to help ya.We need to know what alt is on the vehicle I am assuming a gm 10si if so with the plug out of the back of the alt there should be no light and both terminals will have voltage with the key on. #1 is the feild circuit this controls the lamp power comes thru the bulb to the alt where it grounds turning on the light.Once it begins charging positive voltage at the alt. end of the wire removes the ground shutting out the lamp. terminal#2 is the sense wire it should read battery voltage.If the lamp is on with the connector unplugged there is a short to ground in the light circuit that must be found.Good luck.

[67Mustang Al.]

Some alternators require an "excitor " circuit before they will put out a charge. If you have a new wiring harness there is a chance your alternator is looking for an extra circuit to allow this to happen. A mate of mine with a BMW 3 had this problem .Maybe your new harness needs a look to check the "field" charging colour code. (white for 67 Ford Mustang) Auto electricians will know the answer whether your alternator requires this type of configuration. Your red alt.dash light should go out when the alternator is putting out a charge.
Regulator will need checking too.
Cheers
Al.

[302 Z28]

I second the suggestion of the base car hobby shop if you have one. When I was in the USAF stationed in Abilene Texas we had a superb base auto hobby shop. I have very good memories of helping and receiving help from people, made some life long friends too.

Vince

[barnym17]

The brown wire on terminal #1 is the field wire or ecxiter if it's a 10si.

[usmcsawgunner]

sorry to keep you all so long on an update but i put it up on a lift and found the positive battery wire prety much welded to the headers. got that sorted out with a new wire and a different route. then i think it might have killed the battery because when i was leaving the hobby shop it died twice and everything got dim. the hobby shop guys said the battery was bad. anyway my question now isthe #1 terminal on the back i have a jumper that goes to the stud on the back of the alt. then i got the brown wire that goes to #2. do i have that backwards? the brown wire goes to the alt light (duh) im pretty sure thats how the hot rod wires (harness man.) guy said its supposed to be ran. i could very well be wrong tho...help me ye of mighty electronic wisdom...

[barnym17]

On top of the alt is a 2 terminal plug it is marked on the alt. case.1 and 2.the brown wire goes 1 the jumper to the battery stud goes to 2.

[usmcsawgunner]

so thats how i have it but the alt light is still on. i havnt checked if its charging or not yet. (havnt had the time) anyway is there a way that i might have wired the light wrong and thats why its not charging? is there a specific ground you have to use for that light? im lost...i think i wired my voltmeter wrong too. i dunno

[El camino]

It is possible that the light is wired wrong. There is no designated ground for the light, other than inside the alternator itself, which switches the ground on or off depending on system requirements. If you unplug the connector from the alternator and the light still comes on when you turn on the ignition switch, then that will need to be corrected first, which means you gotta track that sucker down!.
If the light comes on while unplugged from the alt, recognize that the light bulb wire is getting a ground from somewhere else. Are you sure you have it wired the right way? There should only be a wire from the switched ignition source to the light bulb, then from the light bulb to the alternator connector terminal 1...It only comes on when you turn on the igition switch right?

If it is wired correctly then you've got a short to ground between the bulb and the alternator, pure and simple.
Check the wire from one end to the other starting with the alternator connector. Be sure you don't have a strand of bare wire shorting to the other terminal, for example. It only takes one strand to cause a problem.
Try to get an eyeball on every inch of wire back to the light bulb. Look for signs of chafing, and any possible points of puncture for sharp edges or screw points. Look for slack or unsecured sections that can move around; tie anything down that moves much at all. You get the picture. Be very picky about everything!

Jeff

[usmcsawgunner]

Jeff you were right on!
what i had done was cut off the light socket from the wiring harness to use the existing one from my truck and i just used a common ground. so i fixed that. but was that THE problem with charging though? it seems that there should be more to the problem. OHH by the way i did figure out the battery i had didnt have enought cold cranking amps (it only had 500) so i got one that has like 720 or something and it starts fine everytime so far but even with the less CCA's the battery would just sit and die....anyway ill let you guys know later on but i have to fix a mushroomed pushrod too!
my motto for my frankentruck is one step foreward three steps back!

[cobalt327]

Originally Posted by usmcsawgunner

my motto for my frankentruck is one step foreward three steps back!

Heard that!

Does the NEW battery still go flat?