Alternator?

[frankthomas]

Hi.. I have a 1989 Celebrity bow rider with 5.0l Mercruiser. Dual batteries. I usually run with both batteries. Problem is while running with no accessories on, voltmeter reads right at 12 volts. Turn the blower on and it immediately reads10 volts and quickly goes into yellow then red on the gauge. Turn the blower off and right back to 12 volts. It starts strong so batteries are good, about 4 years old. Does this sound like an alternator going bad? Thanks

 

[Scott Danforth]

it sounds like you have not done any troubleshooting.

dash gauges are notoriously inaccurate.

so take a good DVM..... and start troubleshooting.

could be bad connection
could be bad gauge
could be bad alternator

 

[Chris1956]

Put a voltmeter on the battery posts. Measure voltage. Start boat at idle and turn on blower. Read voltage. Now rev motor up to 1500RPM, and reread voltage. If it is still under 12VDC, the alternator is not charging.

Make sure all wires on alternator are clean and tight. Some alternators have a heavy charging wire plus lighter reference voltage wires. Make sure you check them all to see that they are not corroded or broken.

have had battery cables rot out under the insulation. You see a bulge and it feels different then the rest of the wire.