85 suburban burning up alternators

[mw4titans]

i have been through 3 alternators in 5 days. i had the last alternator checked before leaving the store and it tested at 15 volts but after i hooked it up it seemed to be doing well by the gauge in the truck but before i could hop out and check it the votage, it had dropped fast to under 13 on the gauge so i put a voltage tester on batt and it was just showing 12.5 volts.. this was a new alternator not rebuilt..any help or ideas i would be gratefull.

btw... hello everyone im new to this forum sorry i came in with my hand out... sorry if this post is in the wrong place.. thanks in advance for your help

 

[BlaKK54Speed]

i dont want to make you sound dumb, did you make sure you hooked the terminals up correctly? is there something putting load on the alternator? (amps or other aftermarket equipment) is the parts store checking them to see if they are fried?

 

[mw4titans]

no worrys, and yes i have it hooked up right, well i have the 2 wire connector pluged in as it should be and the red batt connector bolted on back.. i had the last alternator check at store and it was putting out 15something when checked on machine before i left with it. now its only putting out less then 12 with only engine running . no i havent hooked any after market acc's not even the radio has power to it.

the alternator two wire plus does have some burn marks on the ends. some plasic melting so i assume it shorted at one point in time. the way the plug goes in , is brown wire is going in #1 and red on #2 is that right?

 

[BKinzey]

It shorted at one point in time?

Did you fix the short? They don't fix themselves!

Check your wiring, if the wires shorted out they probably still are

 

[mw4titans]

the problem is i just got the truck from an old lady that husband had passed.. i have only had it for a week so all is new to me. i know it has a rebulit jasper engine in it from the docs in the glove box so maybe something wasnt wired back up right

ill trace the wires back and see what i can find.. thanks for your input

 

[goldwing2000]

Definitely sounds like a shorted wire somewhere causing the alt to overload.

 

[BlaKK54Speed]

i would get some diagrams and make sure all the wires are connected to what they are supposed to be connected to, anything can cause a short, dont take much

 

[goldwing2000]

How it should be hooked up from the factory:

Main output wire: from back of alt to B+ terminal on starter with fusible link inline. Should be 10 ga or bigger.

#1 terminal: should go to dash gauge or light

#2 terminal: should go to junction block on firewall

Make sure you have a good ground, too. If the bracket attachment points are rusted out or painted under, you won't get a good ground.

If you end up needing a new plug and can't find a good one locally, see the folks at M.A.D.

 

[mw4titans]

thank you for your help, i couldnt find the short or break but i took a short jump to the junk yard and pulled off the wires i need to test . hooked it up and the alternator is putting out over 13.4 volts at idle.

btw ty for the m.a.d link ill get to ordering one now that i know the problem.. thanks again for your help and letting me steal knowledge from you guys (was looking for the beer smilie, feels like i owe yall a couple) thanks again