Here's my prob: With the headlights, front defrost (or A/C), and the radio on, the voltage guage says I'm running just over 13. If I then turn on the rear defrost, it goes below that, below even 13 -- worse at idle. I know it's a big back window with alot of those little wires on it that draw tons of current, but is this normal? It came with the 78 amp generator according to the RPO decoder. I haven't checked the thing yet because it's in the body shop (some jerk keyed it! I know who it was, but can't prove it ). Oh, and can I upgrade the alternator to one with a higher amp rating, or will this blow fuses?
Thanks in advance.

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Ludicrous Speed GO!!!

Hey, everyone come to the Vicksburg Old Car Show (in Michigan) next year, and hold it up for all the thirdgeners out there.
e-mail me for directions, dates, etc.

[This message has been edited by MartyMcFly (edited August 07, 2001).]

 

What you described is normal. Especially using the rear defroster will present a large load to the alternator. Since the alternator is at it's lowest capability while at idle, it is normal for the voltage to go so low.

Remember that normal maximum battery voltage is 12.6 volts, so you can believe that as long as the system voltage is over that, that the alternator will be providing the current. Any time the voltage is <12.5 volts, you can presume that the battery is providing most/all of the current.

Upgrading to a larger capacity alternator is simple. There will be no danger of blowing fuses. If anything, ensure that the output wire from the alternator to the positive terminal is thick enough for the higher capacity alternator.

105 amperes should be enough for what you described.

 

I am trying to go to the 140Amp unit, but the connector is different. My old one has the very iimple two pin connection (and batt. term.) while this newer one I salvaged had more like a "weather-pack" style, withe 4 pins, one large & 3 smaller. Will the unit still wire-up to my 86' ROCK? Matt