Larry,

If the trim pump has a direct short in the motor it puts a large electrical
load on the system when used against any resistance whatsoever. When the
engine is running it would put a large load on the alternator. If the
alternator is belt driven it could well cause the alternator belt to slip.
OTOH, it could simply be that you need a new belt or to adjust the old belt.

Good luck.

Butch
"Larry Crowe" wrote in message
...
Get a squealing noise from the water pump /power steering belt areas
whenever I trim up or down. What I noticed is that it does not squeal
when trailered out of the water just trimming off the battery.. If I
muff it with engine running I get the squeal when trimming, don't really
understand why ?? Larry