1980 Ski Tique - Alternator

Hi All,

I'm also replacing the alternator, the wiring on the replacement alternator is a bit different.
I need help figuring out how to connect the 4 wires to the new alternator.





thanks in advance!

Sierra Marine 18-5957 Alternator (3-Wire). 68AMP

Yes I do have an ammeter on the dash. Yea the boat has been on the driveway waiting on parts for couple weeks now and the pine needles are relentless this year

fantastic, thank you Keno!

The easiest way to do this is to take your alternator and hook the RED wire to the output terminal as shown in the picture. The RED is the voltage sensing wire that can be used to sense voltage at a remote point in the system. In your boat with not much in the way of electrical loads, running the red wire to the output terminal works fine.

You'll be removing the old external voltage regulator from the back of the engine since the Delco is internally regulated.

That will temporarily leave you with three unused wires in the harness to the alternator.
The brown, the green and the black and there will be a purple wire from the ballast resistor upstream side that will be temporarily unused

The black can be hooked to the ground tab on the alternator and grounded anywhere on the engine.

Now you need to get excitation power to the black wire on the alternator. It needs to come from the key so that when the key is on you have power to the black wire and when the key is off power is removed. The easiest way to do this is to take the purple wire from the ballast resistor that went to your voltage regulator and connect it to the green wire and hook the green wire to the black wire from the alternator. (or run a whole new wire to avoid multiple splices if you want to) Take the brown wire and tape off the ends, it won't be used

As far as issues, your original alternator was 37 amps and the 10 gauge wiring that runs up to the ammeter and eventually back to the battery was sized to handle that with some extra margin .

68 amps is too much if you were ever putting all 68 amps through that wiring. It's improbable that you would, but to keep your system operating under conditions it was designed for, I'd put a 40 amp fuse on the alternator output so you can't overpower the wiring.

Also if you get this all wired up and start the engine and then it won't turn off, it means the alternator excitation line is backfeeding the ignition system and you'd need to put a diode in that line to prevent backfeed. It most likely won't be an issue for you but I figured I'd mention it.

The second picture is a pretty ugly marked up drawing of the original wiring showing the Delco hookup.

The third picture is the original wiring with the Prestolite alternator and external regulator just to have something to compare to.

On the mechanical side of things, you'll probably have some minor shimming to do for belt alignment and the bottom mounting hole on the alternator will probably need to be drilled a little bigger to fit the PCM mount and mounting bolt.

It's really not hard to do this installation. It was a lot harder trying to put all this into a post though.