Alternator problem

[JusDreaming]

a friend of ours has a catalina 34. While cruising this year his tach started acting wierd. When at idle it reads about 400 rpm, when actually the engine is at about 1000rpm. When you rev the engine the reading on the tach goes down to zero. We checked the belts and wires but saw no obvious problems

[Alan Wheeler]

It is possible the brushes need cleaning.

[JusDreaming]

Originally Posted by Alan Wheeler

It is possible the brushes need cleaning.

not sure, It seems to be charging correctly

[starfish62]

If the tach grounds out when the engine is revved, I'd suspect the tach itself. Check the connections to the tach (any corrosion at all should be cleaned up--some 400-600 wet/dry sandpaper) and then hit it with some CRC & try it again.

[starfish62]

If the tach grounds out when the engine is revved, I'd suspect the tach itself. Check the connections to the tach (any corrosion at all should be cleaned up--some 400-600 wet/dry sandpaper) and then hit it with some CRC & try it again. You can hotwire the tach to see if the guage is working. I think you should be able to take your lead to the block and put it to ground (engine NOT running, batteries to off) and the tach should peg at max. At least then you'll know that the guage is good.