Mercruiser Alternator

[Mr. Sandman]

I've installed a lot of marine alternators, and various current and voltage measurement devices. I am assuming this is on a merc inboard or I/O and not an OB.

You might have done all this but you you really need to check your batteries and connections, that they are clean and solid. (and properly wired with the proper gauge wire and that the wiring is in good shape)

Re- check all grounds.

What is the voltage on the battery itself as measured at the battery posts?

What is the the voltage at the alt, engine off?


What is the the voltage at the alt, engine on?

This sounds like a dumb question but are you sure it is turning in the right direction? Double check all the instructions and make sure you have all the connections and any switches or rear-wiring positioned correctly.

Does this unit have an internal or external regulator? Make sure it is set for the appropriate device.

Let us know how you make out. It is highly unlikely that both units are bad. They are tested before they leave the factory so they probably work fine.

[nightfighter]

Check the coil.... Had a 28' Pursuit with twin Merc IOs. Had to carry spare coils all the time. Those Mercs would burn them out. I'll look to see if I still have one in the shop, even though that boat has been gone for ten years.

[thefishingfreak]

you have to goose the gas a little to excite the alternator first.
Some will self excite. Some just wont.
I have twins. one will-- one will not.
I have to goose it a little to get it going then it's fine