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Midwest Puddle Pirate
2,160 Posts
Discussion Starter · #1 ·
Just a little heads up for those who own Volvo Penta diesels. I helped a friend solve a mysterious and terribly intermittent loss of power problem on his 2001 Beneteau. Every time he really needed his engine, it had no power to the instrument panel, and of course wouldn't start. He and a friend could get the engine to fire by supplying both power and ground to the starter solenoid.

When I was finally able to see the problem occur, I found that there was power to the instrument panel through the "instrument lights" switch. This switch powers everything and should be labeled "master". So I knew I had a ground problem. The wiring diagram shows that the instrument panel, both warning switches, the starter relay, and the starter solenoid all ground to the back of the alternator. The alternator diagram shows what appears to be a ground through the case. I pulled the alternator off, expecting to find a corroded ground wire to the back of the alternator. The wire wasn't corroded. Stuffed behind the alternator I found a 12 gauge wire with a boot on it that I hadn't removed. I followed the wire, and found that it attached to the same bolt as the main ground wire from the battery to the engine. Apparently the system had been grounding through the alternator case ever since this wire had been left off, possibly for years, until one day it didn't. The fat ground wire was there to make sure it continued to have good ground.

So if you own a Volvo Penta diesel, don't forget the large ground wire to the back of the alternator. If you do, the gremlins will come visit you months or years later.

Incidentally the Volvo manual that can be found online shows a ground wire from the back of the alternator to an unidentified item, and back to the battery. The Beneteau manual just shows a ground schematic symbol at the alternator.
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