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.

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.

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.

Glad you got it figured out