'73 Mercury 500 not charging

reelfishin

Captain
Joined
Mar 19, 2007
Messages
3,050
I picked up a parts boat today, I was told that the motor didn't run but figured I'd give it a shot anyhow and it started and ran fine, the only thing I found wrong is that it don't seem to charge the battery?
How much do these actually charge? Should I see an increase in volts at the battery once the engine starts? It started right up I was actually surprised since I was told it was junk.
Even the water pump seems to be working fine. I let it get warm, then I shut it down and did a compression test and all 4 read 133 to 138psi. The prop is a bit rough, and it's stuck on, (like the other four Mercs I have here), but the rest is pretty clean. It's another short shaft though, and it's mounted on a 20" transom, so it couldn't have performed very well.
Both the boat and motor look good, with only some minor issues with the interior. The trailer needs some attention but the frame is sound, The coupler is bent and I had to drill a hole in the ball coupler to tow it, it was a take it now or never deal. I towed it about 20 miles with a bolt through the coupler and secured to my hitch. It's not the safest way to tow, but I took it easy and kept checking it and made it home. I got the impression that the old owner just got frustrated with it or ran out of money.
 

WillyBWright

Fleet Admiral
Joined
Dec 29, 2003
Messages
8,200
Re: '73 Mercury 500 not charging

I'll bet they had the battery hooked up backwards. Then the starter would spin backwards and never fling up to engage the flywheel. A few might be frustrated by that and if they had other problems due to unfamiliarity with all the nuances, give up and get rid of it. Sort of a final straw kinda thing. I got a boat once just because the fuel line was connected backwards.

Most charging problems are due to blown recitfiers. That can happen from corroded, loose, or crossed battery connections. Voltage should rise with RPMs, but idle might be insufficient RPMs to charge.
 
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