I posted this yesterday in the 67-72 group but didn't get any bites. Anyone?
jor
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67 F-100, 352, 4spd
OK, here's the deal. I have a pretty new alternator and voltage regulator. My voltmeter (after-market) was indicating 14 volts or so when driving and everything worked fine. However, after sitting for awhile, the battery would only run the starter for a short time. In other words, the battery wasn't holding a charge. It's an old battery so I figured it was time for a new one.
Initially, I screwed up and got a battery with the poles mounted on opposite sides of the original. I wasn't paying attention and, as a result, dropped it in backwards. When I touched the cable onto the positive terminal, the system objected strongly with a big spark. I took out at least one fuse (my MP3 player, hope it's a fuse anyway). Anyhow, I got the right battery and installed it correctly.
So what's the problem. Well, I turn the key to the "on" position and the voltmeter indicates about 10 volts. I think,Profanity Removed!!! Then I start the truck (turns over just like it should) and drive off. Now the voltmeter indicates a little over 12 volts. AnotherProfanity Removed!!! After driving a few miles, the voltmeter climbs to the regular 14 volts at speed and drops to 12.5 to 13 at idle (650 rpm).
Could I have screwed up my voltage regulator, my alternator? Help!
jor

 

When you reverse the battery, you have a direct connection to ground via the diodes in the alternator. Since you are getting some charge, you probably only blew up some of the diodes. You can get a rebuild kit for $13. I recently did an alternator that had 3 open diodes, was using it that way for years. :7

 

Thanks for the quick response, Mike. So, would AutoZone and PepBoys have the kit? I remember replacing brushes on VW generators years ago but don't really know anything about alternators. Do I have to pull the pulley? Thanks.
jor

 

Pep Boys has the kit. It has the diode pack, brushes, and the front bearing. You do not have to remove the pulley except to replace the bearing. You have to unsolder the stator leads to the diode assembly, should have a fairly large iron. It is easy to do. You put the brushes in the holders and use a small wire from the rear to keep them in place when you put the front of the alternator back in position. You then pull out the wires and the brushes make contact with the rotor.

 

I agree with MikeW. If you burn out one or two diodes, you will still get juice, but not as much as you should (not enough AMPS under load). When all your power options are turned off, and/or engine revving above idle, the voltage will read fairly good. But let idle drop, and/or turn on heater, headlights, radio, etc, voltage will drop so low, it will barely charge the battery (or actually allow battery to DISCHARGE).

 

 

Hey jor, have ya' had any luck????????????