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David McLaughlin's Avatar
 
Join Date: Jun 2000
Location: Burlington Massachusetts
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Question Lights drain the battery

The battery was new as was the voltage regulator. If I run the lights for more than an hour, the next times I start the car, it starts slow. If I put the car on a charger it will start and run fine until I use the lights again. If I've run the lights for awhile, the lights will dim while sitting at red lights and brighten again once the motor is reved up.

The lights are Euro H4s with the lower wattage bulbs (not 100W). I know nothing of the alternator. Actually, I don't even now where it is exactly but I assume it's a stock, factory /6 unit.

Thanks,
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David
1970 914/6 RustoMod
2015 Mercedes E400
Old 09-26-2005, 02:17 PM
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have you put a voltmeter across the battery while it is running/idling to see if it is 13.5 volts or more?

If it is charging just fine, then you may not have enough alternator output if you added a bunch of electronic stuff to your car. You want your alternator to put out enough current to drive everything (you should never rely on a battery to run stuff - it is a storage device), so add up all the max current draws and see what you have. I have a bunch of electric stuff on my car, so I have a "110 amp" alternator, and if I had everything going at max, I would be at 110-115 amp draw. the spec card that it came with said 80 some amps at idle and 117 amps at high rpm.

Because the lights dim at idle, I suspect you don't have enough output at idle now and need to get a larger amp alternator.
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Tim
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1972 914 1.7L turned FW190-V8
353cube 525HP SBC with Mendeola S4 transaxle
Old 09-26-2005, 03:07 PM
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I have zero electronics. I'm wondering if the alternator itself is gone.
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1970 914/6 RustoMod
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Old 09-26-2005, 03:37 PM
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maybe - just need to throw a voltmeter across the battery while it is running and see what the running voltage is at the battery, should be around 14 up 14.3 volts, maybe 13.5 but no less. If the battery shows 12 or 12.5 volts when running, you have no charging.

If you are low on charging voltage at the battery it is typically the alternator, maybe the wiring has broken down a bit or corroded, but that is the rarer case.

1. check charging voltage, if isn't charging
2. remove alternator and take with you to buy a new one. Ask them to check to make sure the alternator is shot.
3. If the alternator is shot - then you have your answer, new alt. If the alt is working, then there is a wiring issue between the battery and alt.

If you don't have a voltmeter or multimeter, I would suggest just buying one - I have a Sears multimeter that has lasted me well over 10 years and I rewired the whole car (among other things). If you have a 914 and don't have a multimeter, good luck. The wiring on these cars is horrible and breaks down with time (they pretty old cars now). I trouble shot more than one "this light quit working" issue and a multimeter is cheaper than one hour at a mechanic anymore.
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Tim
www.negativereinforcementracing.com
1972 914 1.7L turned FW190-V8
353cube 525HP SBC with Mendeola S4 transaxle
Old 09-26-2005, 04:05 PM
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Good info I remember checking these things a long time ago and ended up buying the VR. I just bought a new Optima (last one didn't like arc welding a wrench to the chassis) so I want to make sure it lasts. I'll check those things. I remember reading a Pelican article on testing an alternator; I'll need to reread that one too. Then I'll try to find where the factory hid it. Could b time to join the firewall hole outlaw gang.
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1970 914/6 RustoMod
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Old 09-26-2005, 04:56 PM
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The alternator can be removed with the engine in the car, either very carefully through the front, or easily if you remove the carbs, their manifolds, and the engine cooling shroud.

Have you checked your alternator charging light on the dash? It should be on when you turn on the key, then go out once the engine starts. Lets you know if your alternator is working. If it's always off, the bulb may be burnt out so you're not getting excitation current to the alternator windings.
Old 09-26-2005, 08:22 PM
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Nope, didn't check that but I just added it to the list. Thanks!
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1970 914/6 RustoMod
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Old 09-27-2005, 08:15 AM
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