89formula#1

Hey guys my buddy has a 91 firebir di belive it is, its got a 305 tbi and he was changin his vale covers and touched sometin on the alt with it and fried the alt. he got a new one and got the battery checked and all is well but his car will not read more then 11.9 volts while running. now what do you think this coudl be?? I haven;t looked at it yet but i a guessing he didn;t hook it up right or he fried the wire that turns the alt on so it can charge the battery

Morley

11.9 V on the stock guage? Don't trust it, put a volt meter on it and see what that says.

TPI86TA

Im having a very similar problem with my 86 trans am.The other weekend i gave a guy a jumpstart and i did the big no-no,I put the jumper cables directly to both our batteries.Since then i notice my voltage started to drop more and more till a day or 2 later the battery died.I figured i fried my alternator so i took it back for a new one.The guy at pepboys said my alternator was fine.But i insisted on a new one.I used my other car to give me a jumpstart and the car fired right up but after taking the jumper cables off the battery died and the car died.So now i decided maybe my battery was just beat,so i bought a brand new battery.I put it in and same deal.Id hook up the voltmeter and with the jumper cables on its a lil more than 12 volts,then when i have the car running i pull the jumper cables and i watch the volts drop all the way down fairly fast as if the alternator isnt doing its job.I had this alternator tested too b4 i put it in and its fine and the old one was fine.Any ideas????

89formula#1

well i went over his house tonight to fix it for him and i traced the wire off the alt that says bat. on the terminal. it kept goin then went to a fusible link and the wire comin out of the other side was burnt inhalf, so we put new wire on and it fried the wire. we had to buy actual battery wire, or fusible link wire or sumtin, but we spliced it in and its workin fine 14.9v

TPI86TA

Im thinking the problem hasto do with whatever the brown alternator wire goes to.I tested the voltage going to the thick red wire and its about 12.12 volts.Then i tested the red and brown wires in the alternator harness.The red was at about 12.11 volts.With the car in accessories,the brown read about 15 volts.I think something in that brown line is messed up.As a test,I cut the brown wire and took only the end going to the alternator and applied 12 volts to it and the alternator began charging perfectly fine.Shouild that brown line be giving the alternator some voltage to turn it on and trigger it to charge?Any ideas???Anyone know the places i can check where that brown wire might run.Does it maybe go to my stereo as well as to the ignition and or fuse box???

89formula#1

u got it man, u gotta run the brown wire 12v. i had to do it to my car when i switched to carb.

Momar

The brown wire is the turn on wire. It should be to an on with key source so the alt doesnt burn its self up by being turned on when the car is not running. I think that the factory route comes from the gauge cluster or something. The reason I even looked at this was because I put a 140 amp alt in my 85 ta out of a 94 or 95(not sure which) LT1. Anyway, I had to hook up that brown wire to the turn on wire on the alt. The other wire that my car origionally had from the connector to the terminal for the battery on the back is probably for the regulator so it knows how much voltage it is putting out. On the LT1's and probably newer thirdgens(didnt look at the diagram on the newer thirdgens) this connection is made inside the alt so I didnt need the wire going from the connector to the bat terminal on the back.

Ben

Momar

double post

TPI86TA

ok cool,thanks alot guys.So maybe ill try running it to an accessories wire then.The only thing that scares me is that when i give that brown wire juice,the alternator then squeals loud,when i take the voltage away from the brown wire the squealing stops.Im just scared the squealing might be me burning something up when i do that.

Momar

Well, I am no pro. Dont take my word for it. Look up the diagrams yourself. One thing I will say is a alt will make louder noise then usual when it is charging a battery that is not fully charged but I wouldnt think it should be real loud. Also, since it is just a signal wire it may not be supposed to recieve a full 12 volts. Also, did the brown wire read 15 or 1.5 volts when you tested? I used my factory turn on wire but a newer style alternator so I dont know what hooking up a normal power wire will do other than if you hook it up so it is on all the time it will burn it up.

Ben

TheGreatJ

Brown is the "field enable" wire. It basically turns the alt on and off.

When I stripped the TBI and switched to carb I had this problem. You can run the brown wire off ignition power (that's how mine is) and it will work fine. I once read somwehere that you're supposed to put a resistor in the circuit but I never did and haven't had a problem with it. You can also loop the red wire on the connector to the post on the back of the alternator and simplify things a little bit (if you're rewiring the whole circuit like I did.)

The squeal may be the belt slipping......when you turn on the alt it creates a load and slips, when you turn it off the load disappears and it quits slipping.....it's an idea anyway.

TPI86TA

hey,thanks a lot guys.Im thinking the resistor thats in the brown line burned up where ever it is.Im also thinking maybe im not supposed to have the full 12 volts and the resistor stops the alt from getting a full 12.I think im gone see if i can find the right resistor and run a line to the ignition and see how that works.Does anyone have any idea where in the line the old resistor might be located???thanks