Mercruiser D254 Starter/Alternator wiring help needed

[Andy_Sydney]

Hi,

I have purchased a new alternator (from ebay) for my 1993 D254 4.3 Turbo Diesel. The wiring diagram in the manual shows where the colored wires go on the original but give no information about where they should go on the new one.

On the wiring harness from the engine i have:

Red (Alternator Output)
Black (Alternator Negative)
Grey (Tach)
Brown ??



The brown goes back to the starter relay circuit.



I have tried attaching the brown to the purple on the alternator but it won't make the relay kick in. If I connect a wire from the brown on the starter relay straight to the battery negative, the engine kicks over no problems.

Does anyone knows how I should connect this up?

Many thanks in advance
Andy

 

[Andy_Sydney]

Re: Mercruiser D254 Starter/Alternator wiring help needed

Here is the wiring diagram from the manual...

 

[Fun Times]

Re: Mercruiser D254 Starter/Alternator wiring help needed

Is that an OEM alternator or aftermarket?

Do you have the original alternator to compare the two side by side to see where the brown wire should go/plug into?

On the wiring diagram you posted, where does the other end of the brown wire go to? Not the brown wire that cut's off to the relay in your photo, But the brown wire that goes straight up but is cut off.

Sorry, I'm not familiar with your engine model to be able to help much.

 

[Andy_Sydney]

Re: Mercruiser D254 Starter/Alternator wiring help needed

The alternator is an aftermarket version...
Alternator Mercury Mercurser 805884P 805884T 12176 | eBay

I recall it was around $600 for a genuine one.

The old alternator:

The brown was connected to D+

 

[Andy_Sydney]

Re: Mercruiser D254 Starter/Alternator wiring help needed

Is that an OEM alternator or aftermarket?

Do you have the original alternator to compare the two side by side to see where the brown wire should go/plug into?

On the wiring diagram you posted, where does the other end of the brown wire go to? Not the brown wire that cut's off to the relay in your photo, But the brown wire that goes straight up but is cut off.

Sorry, I'm not familiar with your engine model to be able to help much.

Also, the other end of the brown goes to the dash (charge light according to the manual), although I don't have a charge light.

 

[Fun Times]

Re: Mercruiser D254 Starter/Alternator wiring help needed

Just so your aware, that new alternator does not seem to match your OEM part numbers at all. Maybe the name but more importantly not the numbers. I believe it may fit your donor engine model (2007 D4.2) but not your 0D00 numbers.

Any chance at getting your full serial number to be sure that this is your correct parts catalog? http://www.mercruiserparts.com/sele...254+TURBO+AC+(BRAVO)++++VM+254+I/L6+1990-1993

The part numbers for your 1993 engines should be 8M0084535 or 816175. None of them are listed in that link that I noticed.
http://www.mercruiserparts.com/Show...93/45.png&inbr=1617&bnbr=270&bdesc=ALTERNATOR

I'd just like to mention that there are a lot of times them low cost aftermarket alternators and starters have a strong tendency to be defective in very short order. I've had some bad luck installing a few of them myself so for now on, it's OEM only to help avoid problems.

 

[Bt Doctur]

Re: Mercruiser D254 Starter/Alternator wiring help needed

Alright , heres how I see it. The brown coming from the relay must go to a ground to operate, the alt pic shows a neg ground stud, thats where that brown wire shoiuld go. the Yellow/red is supplying 12v from the start circuit.to the relay coil, the brown wire is the neg side of the relay coil thats needs to be grounded.

85 and 86 are coil wires. need 1 hot and 1 ground to operate

 

[Andy_Sydney]

Re: Mercruiser D254 Starter/Alternator wiring help needed

Thanks guys, I found this image showing a similar set up.



The brown wire from the starter relay needed to go to the warning lamp pin in order for it to work.
The two wires coming out of the alternator needed to go to an ignition positive.

The alternator puts out around 14v when running. Another problem solved, thanks guys

 

[Bt Doctur]

Re: Mercruiser D254 Starter/Alternator wiring help needed

The two wires coming out of the alternator needed to go to an ignition positive.

Thats wrong, one is a sense lead that goes to the battery, the other is an excite lead that goes to a switched 12v

 

[Andy_Sydney]

Re: Mercruiser D254 Starter/Alternator wiring help needed

The two wires coming out of the alternator needed to go to an ignition positive.

Thats wrong, one is a sense lead that goes to the battery, the other is an excite lead that goes to a switched 12v

Ah thanks BT Doctur, if I run a wire from the big starter positive to the sense, will this be ok?
The batteries are quite far away from the engine. It would save more messy wiring running around the engine bay...