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WJM 12-16-2012 10:33 PM

Help Volvo MD5A idiot light wiring
Trying to get all the original idiot lights working on the boat I just bought. It's a Santana 28 with a Volvo MD5A diesel the oil pressure and water temp are pretty straight forward but having questions on the charging light the wiring diagram shows it going to the alternator but I'm sure where. The alternator I have is not the original also. There are a black & white wire coming out of the back of the alternator (see pic) the black goes to charge the battery the white goes to nothing? But when I connect to that, the initial alarm sound check at ignition drops in volume and just doesn't seem right? Any ideas?

hellosailor 12-17-2012 10:34 AM

Re: Help Volvo MD5A idiot light wiring
You'll have to post the alternator make and model for anyone to tell you for sure. But no, the black wire cannot be charging your battery, the heavy "pink" one form the alternator should be the charging output. The black might very well be the sense lead, which also goes to the battery positive, assuming there's only one battery and no switch. Which would leave the white for the alarm/alt light, although black/white might be reversed, that's why you need to know what alternator that is or how those terinals are marked.

The pink wire also looks like home wiring, or obsoleted fusible link wiring (now considered a fire hazard) so you might try to see what the printing on it says. And wires should never just run through space, the black and white ones probably should be secured to something and then to the bulkhead, so they don't just vibrate around in the air and then snap off their connection.

I'm not sure how to read the rats nest shown on #12, the original alternator, which seems to have many more connections than what is usual today. (Perhaps for an external regulator mounted on the original alternator, Motorola/Marchall style.) Looks like they took a wire to the "B" connector to feed the alarm system and I'm not sure that what you've got can integrate into that.

WJM 12-17-2012 05:16 PM

Re: Help Volvo MD5A idiot light wiring
Thanks "hellosailor" I will have to take a closer look, I didn't see any markings or labels at all on the alternator but will look again. Will also check out pink wire type.

Rockter 12-25-2012 08:55 PM

Re: Help Volvo MD5A idiot light wiring

The thick red wire is the power delivery to the battery.... it is a positive lead.
I am puzzled as to why the white lead goes nowhere, but the black and white leads look very much like the field excitation leads for the alternator rotor.
There will be a regulator somewhere too, perhaps on the other end of that black lead.

Tell me, when the motor is started and revved up to (say) 2000 rpm, what is the voltage across the battery leads? It should be about 14 V, perhaps a bit higher.

WJM 12-30-2012 11:03 PM

Re: Help Volvo MD5A idiot light wiring
Hi Rocter,
Thanks for the reply, I haven't had a chance to get down to the boat yet. Hopefully this coming weekend. I'll report back what I find.
Thanks again everyone for your feedback.

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