Alternator Problem

D

dinows

Member
Joined
Feb 28, 2002
RO Number
7679
Messages
216
My son bought a 1990 Sea Ray 350 IO and 2 days later it lost all power. So I went down started it up with a jump, put the gauge on and only 7 volts. Pulled off the alternator which had obviously been replaced not that long ago and the large yellow wire was all burnt and melted where it connects to the alternator lug. could someone give some advice ?? Dont want to just replace the terminal as there obviously had to be a reason for this ? Any ideas
Thanks Deano
 
Battery terminals as noted, but be sure to check grounds also. MerC I/Os have multi-pin harness connectors also.

Don't overlook any Battery Switches it has. Those "Red Perko Switches" last a long time but shouldn't be taken for granted. And of coure they too have connections.
 
The overheated wire had too much current from either bad connections, a short, or defective alternator rectifier/VR. Install a good charged battery. Is that yellow wire on the alternator's BAT connection? If so, and there is a short in it, disconnect it and run a jumper wire to the battery. When it charges, the bat. voltage will go from 12v when off to 14v+ when running. If you can find a wiring diagram or manual for your engine on-line and post, it would help.
 
I would first suspect a loose or corroded connection. How big in gauge is that wire and connector?

Double check to make sure its a marine version of an alternator since its been replaced.

Some engines use a single wire alternator and some use 3 wires (all in addition to ground).

On a 3 wire system, two wires are small gauge and one is larger. Could someone have swapped some of those 3 wires? Things might kind of work for a bit with some of the wires swapped, but not well.
 
If the wire is burned it's carrying a whole lot more current than designed, and all that current is going SOMEWHERE. My guess you have a short somewhere, or a bad battery. Inspect your cables closely for worn insulation and grounds.

If you can't find anything haul the alternator in to a shop and have it checked.
 
Most yellow wires in 12 or 24VDC systems are ground wires. I suspect your boat was built before the change from black to yellow was done for DC negative voltage. Just an FYI.
Bill
 
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