# 1991 GMC low voltage & now no charge



## DarinRay (Feb 2, 2002)

Hello All,

Well I really need some help here with my 91 GMC 3/4 ton with a 350. It all started with the truck running fine and having the normal charging voltage of 14.4 or near and once I would put the blower on or any other accessory the voltage reading in the cab would drop when starting and woudl go back up if I shut the item off. I thought it was just teh gauges but then with a multi-meter it would read the same. Anyway I have a dual battery setup to run my plow and there is a isolating solenoid between them with the positive leads joining there with supply voltage to energize the coil leading from the power supply box under dash by the emergency brake pedal(I don't even really know what this is....Another fuse panel)?? So my pea brain thought I woudl start looking into this voltage problem and took the solenoid out and just had the 2 battery positive leads attached together with a bolt and nut electrical tape then put around this and thought I would be done with everything. WELL I started the truck and the charge light on the dash come on and the voltgae was reading ~11.8. :realmad: After a bit of thinking I was like well low voltage was better than no voltage so I put the thing back to the way it was originally and started the truck up again...NO voltage again. :realmad: 

So I thought maybe I shorted something out in the alternator and had the NAPA check it for me which ended up being good and now I'm real confused and really need some heads up here. I've disconnected teh negative termial and am reading voltage between the disconnected negative lead and the negative terminal on the battery indicating a short somewhere I've been told and then proceeded to pull each fuse out of the fuse panel on the front of the dash and I still have the voltage reading between the negatives. So I hope someone out here will have some suggestions for me. Talk to you all later

Darin


----------



## Plowingsince73 (Sep 8, 2002)

Darin, Well I have been lurking around this site for a while and it is about time I try to add something, I think I can help. If I understand your problem correctly I believe I had the same problem on my 93 Chevy. After many hours of trying to figure out my problem I finally consulted our local alternator rebuilder. He checked out the alternator and said it was one of the best he had ever seen. I think he said it had the capability of putting out 150 amps. Problem was it was not keeping the batterys charged all the time. It seemed when I was out working a storm it would quit. When I had time to work on it, it worked fine. 
He told me that the problem was in the wiring harness. The large wire on the rear of the alternator (Bat) runs down to the battery lead (hot) on the starter. Somewhere in that wire is a fusable link. He said that sometimes because of corrosin the link goes bad. Not completly, but when a heavy load is put on it it fails to allow most of the current through. He then took a piece of wire and connected it to the hot side of the battery and the other end to the battery terminal of the alternator and presto plenty of power. 
What you need to do is give this a try. If it works for you just buy a new fusable link and put it between the battery and alternator and you will be good to go. Hope this helps. Tom


----------



## cj3859 (Aug 27, 2001)

*volt drop*

also check your idle speed out make sure its at spec rpm,if its low alt will read lower than normal,then you put on a load and it drops lower yet,mine was lugging at 500 rpm bumped it back up to 700 rpm where i'm supposed to be and alt gage stays steady,lites,turns,heater all on...... just one more of many possibilities, good luck!


----------



## DarinRay (Feb 2, 2002)

Hey thanks guys for the info and I am going to try them out when it stops raining out.  The only problem is that when I took a jumper wire from the hot side of battery to the alternator it did the same thing (no better) I even went as far as make a jumper from the little brown wire off the only other connection to the alternator and that didn't work either. I am not sure if I mentioned this in my original post but the brown wire only has about 11.6V to it and the other battery wire (red) has the battery voltage. I mean if I have power to both these wires shouldn't the darn thing work?

Like was mentioned I am now going to the store and buying a serpintine belt for it because it does look kinds glossy in the groves and back side. Meaning the speed of my alternator may not be where it wants. 

The whole start of this started because my plow wouldn't like up like it should on the plow battery and I thought the isolating solenoid burnt up allowing the plow battery to drain. When I hooked both the + leads together I may have glossed the belt up or something. ????? Thanks again guys and hope this all works

Darin


Plowingsince73
Junior Member

Registered: Sep 2002
Location: Richland, Missouri 65556
Posts: 1
Darin, Well I have been lurking around this site for a while and it is about time I try to add something, I think I can help. If I understand your problem correctly I believe I had the same problem on my 93 Chevy. After many hours of trying to figure out my problem I finally consulted our local alternator rebuilder. He checked out the alternator and said it was one of the best he had ever seen. I think he said it had the capability of putting out 150 amps. Problem was it was not keeping the batterys charged all the time. It seemed when I was out working a storm it would quit. When I had time to work on it, it worked fine. 
He told me that the problem was in the wiring harness. The large wire on the rear of the alternator (Bat) runs down to the battery lead (hot) on the starter. Somewhere in that wire is a fusable link. He said that sometimes because of corrosin the link goes bad. Not completly, but when a heavy load is put on it it fails to allow most of the current through. He then took a piece of wire and connected it to the hot side of the battery and the other end to the battery terminal of the alternator and presto plenty of power. 
What you need to do is give this a try. If it works for you just buy a new fusable link and put it between the battery and alternator and you will be good to go. Hope this helps. Tom 



Report this post to a moderator | IP: Logged

11-10-2002 03:04 AM 



cj3859
Junior Member

Registered: Aug 2001
Location: seattle,wa
Posts: 25
volt drop 
also check your idle speed out make sure its at spec rpm,if its low alt will read lower than normal,then you put on a load and it drops lower yet,mine was lugging at 500 rpm bumped it back up to 700 rpm where i'm supposed to be and alt gage stays steady,lites,turns,heater all on...... just one more of many


----------



## DarinRay (Feb 2, 2002)

Hey thanks guys for the info and I am going to try them out when it stops raining out.  The only problem is that when I took a jumper wire from the hot side of battery to the alternator it did the same thing (no better) I even went as far as make a jumper from the little brown wire off the only other connection to the alternator and that didn't work either. I am not sure if I mentioned this in my original post but the brown wire only has about 11.6V to it and the other battery wire (red) has the battery voltage. I mean if I have power to both these wires shouldn't the darn thing work?

Like was mentioned I am now going to the store and buying a serpintine belt for it because it does look kinds glossy in the groves and back side. Meaning the speed of my alternator may not be where it wants. 

The whole start of this started because my plow wouldn't like up like it should on the plow battery and I thought the isolating solenoid burnt up allowing the plow battery to drain. When I hooked both the + leads together I may have glossed the belt up or something. ????? Thanks again guys and hope this all works

Darin


----------



## DarinRay (Feb 2, 2002)

Well I got the new belt and installed and that didnt' take care of the no charging voltage but I do think it was v'd pretty bad and may be the cause of the lower voltage when turning something on. 

If I have power to the only two wires that go to the alternator and the alternator is grounded good shouldn't I have some charging voltages????? I may end up just getting a new alternator and being done with it but woudl like to hear from everyone here. Thanks

Darin


----------



## firefighter (Oct 23, 2002)

*Voltage*

Check all connections for corrosion. Also sounds like voltage regulator not working. Try a new alternator.


----------



## DarinRay (Feb 2, 2002)

Thanks and I think I'm going to check like you said and even run new wire at least for troubleshooting. Shoot it's going to snow here pretty soon and I'm going to be up the creek.

Does anyone know where the brown wire that goes to the alternator along with the red goes. It's small around 12 awg or 14. 

Darin


----------



## firefighter (Oct 23, 2002)

*Brn wire*

Might go to voltage gauge


----------



## DarinRay (Feb 2, 2002)

Oh boy I don't really want to tear into the dash. Well I think I will try the red wire change and see what happens. I also may just end up buying a new alternator and hoping that it fixes it. Thanks again

Darin


----------



## firefighter (Oct 23, 2002)

*DASH*

I don't see any reason to tear into the dash. If charging system worked before the it must be alternator or corrosion in conections. I fuse link going to starter. I'll bet its the alternator. ( VOLTAGE REGULATOR )


----------



## DarinRay (Feb 2, 2002)

Well I took the alternator back to autozone and wasn't going to leave there without a new battery(thought maybe shorting out) or a new alternator. I took both in and tested both and low and behold the alternator was bad this time around and battery was good. New alternator put in and now it's charging back to before. I still have the low voltage reading in dash when I turn a fan on, or lights, etc and still don't know what's up with that but at least I can run her down the road. Thanks for all the help

Darin


----------

