heathrobinson
Part of things
Broken everything
Posts: 848 
Club RR Member Number: 111
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Can someone refresh my memory on how you test an alternator with a test light? My brain's feeling particularly leaky after the weekend, and it's been a while since Iwasshown how to do it, google's being a chocolate teapot, and I'm pretty close to torching the whole damn truck... I hate hunting wiring gremlins.
Ta!
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Voltage across the battery with the engine off, then again with it running, should be 14 something volts running, 12ish with it off.
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As above, you need a multimeter not a test light.
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1988 Mercedes w124 superturbo diesel 508hp
1996 Mercedes s124 e300 diesel wagon
1990 BMW E30 V8 M60 powered!
1999 BMW E46 323ci project car
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heathrobinson
Part of things
Broken everything
Posts: 848
Club RR Member Number: 111
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Nope, sorry. There's a simple procedure to test the spade terminals of an alternator with a test light (e.g. an indicator bulb) to check a. what they do (in case it's not clearly marked) and b. that they're doing it. A multimeter will only show you if the batteries are being charged or not, whereas a test light can tell you if the cause for that is within the alternator, or in the rest of the vehicle. It's a really useful trick, and one I'm kicking myself for forgetting.
It's a case of "connect a lead to (Neg or pos), prod terminals with the other lead, watch for illumination", but I can't remember which terminal I should connect it to, and don't want to back-feed something that doesn't like being back-fed and make my problems worse.
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heathrobinson
Part of things
Broken everything
Posts: 848
Club RR Member Number: 111
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Finally found a portion of it shown in a youtube vid! It's about 12m into this, but just covers living up the charge light terminal with a test light, to prove whether the alternator is working ok. It's a really useful trick, and shows quite quickly whether your problem's inside or outside the alternator.
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Ah, so you wanted to know how to test the wiring not the alternator?
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1988 Mercedes w124 superturbo diesel 508hp
1996 Mercedes s124 e300 diesel wagon
1990 BMW E30 V8 M60 powered!
1999 BMW E46 323ci project car
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