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Battery light coming on

G

gregn96cuda

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Location
El Cerrito Ca.
I replaced my alternator with a rebuilt one after I removed the belt and the bearings were squeaking. The light is off now but still not putting out more that 12 volts according to the gauge. I had the old alt checked and it was fine except for the dry bearings. Would this be a problem with the dreaded dirty ground wires? Any suggestions other than cleaning them? I'm taking a new girl to Stinson beach tomorrow, and I don't want dead batterys, while we are out on our 2nd date.

Thanks for any advice...
 
Checking grounds is the next step and the likely culprit. Not to mention free except for your time.
Good luck with the date!:thumbsup:
 
If you don't want a breakdown on the 2nd date - find another girl. :skep: (6.5 or Woman...)

I would double check the big charge wire is installed on the alternator. Then get a real voltmeter and check the voltages. You want 13.5v give or take at the alternator charge wire bolt. You want higher voltage after the truck is running then before you started the truck. You want 12.8v give or take with the engine off. 12.5 v or less start suspecting a bad battery. 13.5 give or take at the battery with the engine running. A bad battery can overheat an alternator and cook bearings.

You may have a dud rebuilt alternator. And with any luck you still have your old one with the special diesel pulley size. Gas engines use a smaller pulley. Most rebuilds come with a gas pulley. Your tach cares about this as it is run off the alternator.

Give or take means the voltage changes with temperature by design to properly charge the battery. The alternator being overworked and generally too small for the job will also vary the voltage. This too small makes them run hot and cook off bearings. There are some threads on here about using a larger CS144 instead of the overworked CS130 alternator.

The 1994 may be like my 1993 with the main positive junction by the coolant overflow bottle. The battery charge wire comes off this and goes to the battery beside the exhaust and starter. The insulation falls off from heat and the wire corrodes, shorts out, and/or burns the truck to the ground. This wire also likes to rub through and short at the battery tray passenger side. It is a good idea to remove this wire and run a bypass. The alternator also runs to this main junction. You want to check both wires for failure. Esp at the alternator where replacing the unit disturbed the wire.

Don't forget to check fuses by removing them and cleaning the corrosion off them.
 
Yes I still have my old alternator. I just checked and I'm going to have to swap the pulleys the new one is 2 3/8" the old one 2 5/8" OD. I also bought 2 new batteries when I changed the alternator, my old batteries were still cranking but slower than they were a few months ago. I need to get a multi meter and check the voltage for sure.

Thanks for the help and advice.

I wouldn't mind breaking down with this woman she's really hot, but she might think I'm a loser driving an eighteen year old truck if it won't start every time.
 
After testing the alternator I was not getting 12 volts at the + lug, but I had 12v at the batteries. I figured out that the duel battery isolator that the previous owner installed may be the problem, so I'm getting rid of the diode type and replacing it with a solenoid type. I'll let you guys know how it works out.

Thanks for the help.
 
why is there an isolator in there in the first place? the dual battery setup is to give you the extra power for staring.

did you check the voltage with the truck off? if so what was it?

last question. how good of shape are the belt/tensioner?
 
I don't know what purpose the isolator served. I would guess they had a trailer with a winch, I just wanted to replace what was there as I also have a trailer with a winch & wouldn't need to carry a battery on the trailer. The truck always started without ever draining the battery. I'll check the voltage at work tomorrow.

The belt's old and it could probably use a new tensioner. I installed a new tentioner on my 89 6.2 because the old one would wear out a belt in 6 months. I wonder if it's the same from '89 to '94? I could rob it from the '89 since I don't drive it anymore... has a dead transmission & weak injector pump. But it does have a red block engine from my dad's old '83 blazer that was wrecked with about 50K miles, now less than 100K.

I also need to remove/delete the vacuum pump on the '94, but I have A/C and think it's going to be a lot of work, that I don't have time to do right now.
 
These are 12 volt systems not 24/12 or 12/6. The batteries should be hard wired in parallel--+ to + and - to -. Alternator output goes to + on drivers side battery and the main cables to starter and fuse panel come from + on passenger side. Both - cables go to engine with strap grounds from engine to frame.

12.6 volt on each battery with cables disconnected is proper for a new, fully charged lead acid battery. When connected and running at high idle they both should have 13.8 to 14.2 volts between the + and - posts and + to ground.

Isolators are used in RV and trailer applications so you only get power to the RV from one battery--can't run them both down. OR they are used to charge the batteries backwards from a generator on the RV or trailer without harming the vehicle wiring.
 
I still need my vac pump but had done this in other applications.. Make a flat bracket that bolts where the vac pump was, get an idler pully, use long bolt and spacer to align. If you do it right you should still use the stock belt and the angles to the other pulleys remain the same.
 
just thinking out loud here

if the isolator failed, the DS would charge but the PS would just drain on each start.

what controlled the isolator?

are you checking both batteries for voltage or just one side?
 
Some isolators are very complex. My Bounder Class A had a 60 pound control box and four switches on the dash. Had four 1500 amp 6 volt batteries tied in pairs plus the start battery across the front bumper. There was an A/B switch, a Batt off switch, an Int/Ext charge switch and an Emergency Start switch that followed the A/B. But then, everything in the coach was three way power.

Some are simple, steering diodes to isolate the wiring from a genny to a couple of relays. I suggest you disconnect all of what the OP hooked up and figure that all out later.

On my old 86 Ford I use dual post batteries, top posts go to the truck as stock, side terminals go to winch and plow controls. You can do the same except the side terminals go to the truck. That way you can disconnect one without disturbing the other.
 
As said, the isolator was not in the original setup of the batteries in this truck.

It needs BOTH batteries to start.

If you need additional electrical juice, put in a 3rd battery that you can use just for that purpose.

DONOT PUT ANY ISOLATION FOR THAT 2 STOCK BATTERIES.
That is the way it was setup from the factory.
 
The date went great and the truck started every time, then after I dropped her off the next time I tried to start the engine it couldn't crank fast enough. So I had to use my booster to start it.

I didn't get to check the voltage at work and I got another even hotter date tonight...taking a 5'10" blond (she runs 1/2 marathons:) to the Red Hot Chili peppers, at the Oakland Coliseum at 8, so I don't even have time to write this post.


Got to go!!!
 
She would kill me if I posted her photo on line. I got my truck working again, I just by passed the isolator and now everything is charging fine. Thanks for all of the advice.
 
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