Electrical issues 1986 GMC

[My 86]

Accidentally left my headlights on last night. Battery of course was dead in the morning. I jump started the truck. It took a few minutes to get enough charge to turn over the starter. It then started up ok and ran fine. I then started driving to work which is about 8 miles from my home. About 3 miles out I noticed that the voltage gauge and temperature gauge were pegged out! I pulled off the side of the road and the truck was running fine and I know it was not overheated. I drove slowly to work and when I pulled into the parking lot the engine began to hiccup a bit. I turned it off and tried to start it and it was completely dead. Battery is new and connections are good to it. Also tested alternator and it tested good. What would cause the gauges to peg out like that??? Could I have a bad starter switch in the steering column or a bad fuse link somewhere?? Did I damage something while attempting to jump start it??? Any thoughts or suggestions would be appreciated!

[roundhouse]

How did you test alternator ?


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[My 86]

I took the alternator to my local NAPA store and they tested it. Which they said it was good.

[IdahoMan]

I jump started the truck. It took a few minutes to get enough charge to turn over the starter. It then started up ok and ran fine.

That's what happended to me the other day.

Why is it that a vehicle connected to another running vehicle still has trouble getting enough power to turn over? Does a running vehicle's alternator supply less power than a fully-charged battery? Is there something in the circuitry that isn't sensing something proper?

[big_al273]

I jump started the truck. It took a few minutes to get enough charge to turn over the starter. It then started up ok and ran fine.

That's what happended to me the other day.

Why is it that a vehicle connected to another running vehicle still has trouble getting enough power to turn over? Does a running vehicle's alternator supply less power than a fully-charged battery? Is there something in the circuitry that isn't sensing something proper?

The dead battery is a load to the running vehicles electrical system and it sucks up available power until there is enough in the battery to allow sufficient current to the starter, bad jumper connections can also cause resistance lowering the level of power reaching the vehicle to be jumped

[blazer74]

New battery after or before? Have it checked or try another.

Good visual on your wiring, specially back of the block by the starter, wiring runs thru a metal tube and can be damaged by heat.

Gauges pegged high or low, open wire somewhere, fuse, loss of ground or short to ground.

[My 86]

Well i found a inline fuse the previous owner installed which was connected to that black two post terminal strip on the firewall. It had a 25 amp fuse in it which was totally obliterated. It referenced back to the alternator and battery. Nothing would work in the cab either when this fuse would blow. I replaced the alternator anyway even when it tested good at NAPA. It seemed to drag. I  checked over all the wiring with an multimeter and found no apparent shorts. Installed the alternator and replaced the fuse. Started the engine and volt meter on dash pegged out. So I shut off the engine. The 25 amp fuse was blown. I looked things over again and found nothing hot or burnt. So I replaced the fuse again and started the engine. The voltmeter was showing around 12 volts which was low. Checked the voltage at the battery and it too showed around 12 volts which tells me the alternator has no output. I took the battery and alternator back to NAPA. The remanufactured alternator was bad and battery was good. I asked for a new alternator not another remanufactured for the replacement. So I did some more research regarding that terminal block on the firewall. I found some schematics showing a 16 gauge fuse link should be there on that terminal block. So I removed that inline fuse holder and soldered in a 16 gauge fusible link in its place installed the new alternator. All seems to be working well . The dash voltmeter reads just over 14 volts and I measure around 14.8 volts across the battery. I don't think that inline fuses should take the place of fusible links! Thanks for the suggestions & comments!