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500 EFI Not Charging

Old 07-12-2021, 02:13 PM
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Default 500 EFI Not Charging

I have a Merc 500 EFI that is practically new, never been in the water. When running I'm only getting 11 volts, tested at the alternator. I had the alternator bench tested and it showed 14 volts on the bench. Could this potentially be a computer issue, or is there something else I should be looking at? I have checked all my grounds, and everything looks good.
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Old 07-12-2021, 09:07 PM
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Okay, you'll have to help me here.
I was under the impression that the last year for a 500EFI was around 2005.
This means "practically new, never ran" could imply a lot of things. Most of the things it implies is that your 500EFI is not "practically new".

​​​Aside from that, alternators are fairly simple, but there are different setups (1 wire, 3 wire, etc).

Take a photo of your alternator and especially any posts for wires, and any plugs.
I believe most of the 500EFIs cane with a 3 wire alternator.

The fat wire goes to the battery + (or to your battery disconnect switch if you have one). The exciter wire goes to a 12v + terminal that is hot when your key is in the "run" position. The sensing wire goes to a 12v + terminal on your main distribution block (some people just jump it to the output wire). An alternator has one additional wire - a very good solid ground wire. Make sure yours is grounded.
when the motor is running, you should have at least 12v+ to ground at the exciter and the sensing wire.
if your voltages are good, then you should pull the brush plate/regulator out and check to see how worn your brushes are, and if your commutator is gnawed up or shows signs od arcing...

But post pictures.
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Old 07-13-2021, 12:12 PM
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Thank you for the reply. It is a Donzi 22 classic that has never been in water, started on the hose a couple time a year to cycle the valves. I picked it up, finished rigging it, and going to use it like it was intended to in the first place.
I did get it figured out last night with the help of a volt meter. The plug or harness going into the alternator had the 12volt pin in the wrong location. I was able to get the pins pulled out of the factory plug and installed correctly and now getting 14 volts. I assume this harness was produced incorrectly from Mercury years ago.
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Old 07-15-2021, 09:24 PM
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Glad you got it figured out
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