A-1 Alternator problems

M

Marlboro Mafia

New member
I have installed two new(rebuilt) alternators on a '81 Rabbit and neither will charge more than 12 volts. Anyone have any tricks or suggestions? All the wires are correct and the belt seems to be tight.
 
Check your grounds, from the alternator to the engine, transaxle to the chassis, and chassis to the battery.

For testing purposes, use a set of jumper cables and ground the battery to the chassis and the battery to the engine block. You may be amazed...

I always used large gauge speaker wire on my A1s and ran additional grounds. Fixed the problems right up.
 
I would agree w/ Greg, check the grounds. Also, w/ the VW alternators, you actually have to 'kick' the exciter circuit to get them to charge. In other words, you have to rev the thing a bit, after it starts, to trip the exciter circuit. I'm concerned by the fact that you say it _only_ charges 12 volts. Have you confirmed that it really is charging? If it is actually putting out voltage, it may be defective. But, check all the grounds first.

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MARRS #25 ITB Rabbit GTI (sold) | MARRS #25 HProd Rabbit
SCCA 279608
 
Bill has a good point. VW alternators will not self excite - they need a "prime" to start generating charging voltage. If your exciter circuit is faulty, the alternator will not charge. I believe the light on the dashboard is part of the exciter circuit. If the alternator light is not lighting when you set "ignition on" with your key, it's a good bet that the alternator will not develop any current. Check your Bentley (sp?)manual. (If you don't have one, this is indespensible for working on Rabbits).

Jim
 
On the ALT,there is a three wire terminal plug,you need to check the wires coming out of that black rubber plug,it may look good but the wires break at the terminal.Check for continuity at the plug. You may need to cut off the old plug and install a new plug or three terminals.
BTW,The same thing happen to me last season.
Good Luck.

ITB #69 VW. ,
 
I was also having some charging problems. Looked High and low for the problem. Instead of looking for deep seated problem, I should have looked at the battery terminal. The clamp was cracked and hanging by a thread. Boy, did I feel stupid!!



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Jeff L
#74 ITB GTi
 
I have been through this problem many times. The VW alternator needs the "Exciter Circuit" to begin charging. On the stock wiring configuration, +12VDC flows from the fuse panel to the ignition switch to the Battery Charge Light on the instrument panel to the alternator.

Initially the voltage flows to the alternator, causing the alternator to become excited via the "Exciter Circuit" explained above.

Once the alternator begins charging, a "counter voltage" flows back to the Battery Charge Light, causing the light to go out since there is an equal amount of voltage on both sides of the Battery Charge Light.

If the instrument panel has been removed to accomodate a new gauge panel, the "Exciter Circuit" has been disabled.

What I do is to run a new wire from the fuse panel to a new +12VDC light on the gauge panel to the alternator.

The infamous BLUE WIRE on the alternator is the "Exciter Circuit" wire. Just attach the new wire to the end of the Blue Wire to reactivate the exciter circuit.

Best check of the alternator is to place a multimeter on the voltage scale across the posts of the battery. If the alternator is charging, you should see at least 13.0 to 14.0 VDC. Good luck, Ryan.
 
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