Mercruise alternator question

[JaseBosto]

I have a mercruiser alternator. It is a spare in case I ever need it. Right now, I need to use it on one of my tractors as it is in need of an alternator. If the need arises to replace the one on the boat, I will then purchase a regular alternator and swap it into the boat. Question: on the back of the alternator there is a battery lug, and a two pronged plug. On that two pronged plug, which prong is the field, and which is the sensing?

 

[Volphin]

Re: Mercruise alternator question

Only use spark arrested alternators for boats. Here are the common types and the wiring for them.

 

[agallant80]

Re: Mercruise alternator question

+1 ^^^

An auto alternator can ignite fuel vapor.

 

[JaseBosto]

Re: Mercruise alternator question

I would never use an auto alternator in a boat. Perhaps I was a little "gray" on that. I mean, I will buy an auto alternator for the tractor, then put this marine alternator in the boat if needed.

 

[Walt T]

Re: Mercruise alternator question

What kind of tractor is it? I like old tractors, just interesting I think.

 

[JaseBosto]

Re: Mercruise alternator question

1961 Farmall 140.

 

[James D. Evans]

Re: Mercruise alternator question

Is there any markings near the plug like 1 and 2, or an S? Looks like a 10SI in the picture. If it is, the pin closest to the lug attaches to the lug. Just run a loop from the pin to the lug. The other pin connects to full 12 volt switched ignition, purple choke wire perhaps. Don't forget to hook the heavy wire that goes to the starter or battery to the lug also. That's how you convert old 6 volt tractors to 12 volt. Done several 8 and 9Ns.

Worst case, a 10SI can be bought for around $30-40 at the parts house. Was standard on most GM cars and trucks in the 70s.

 

[powersail]

Re: Mercruise alternator question

the sensor wire should really connect to the system as close to the battery as possible to make sure the alternator is charging the battery efficiently.

 

[James D. Evans]

Re: Mercruise alternator question

the sensor wire should really connect to the system as close to the battery as possible to make sure the alternator is charging the battery efficiently.

You can run it back to the battery for better sensing, or loop it. Looping it will work if you don't want to run wires. 87 back Chevy trucks I always run the sense wire to the load side of the fuse panel to get good clean voltage to it. What a difference it makes! You can also leave the exciter (field) wire disconnected, the 10SI is internally excited also. Takes about 7-800Rpm to wake it up, so on tractors we always run switched power to them to not have to throttle it up and back down upon start up, and just loop the sense wire.

 

[powersail]

Re: Mercruise alternator question

agreed ^^^