Tach problems(erratic readings) help

[eggsuckindog]

A bad rectifier/regulator on my outboard causes that. The tach is fed from it. What feeds the tach on that Mercruiser?

good question - mine also runs from 1 of 2 recifiers

[bigeasy1]

I'm not sure what feeds it,and unfortunately I can't get back up to the boat for a couple of weeks.
Hope to get up there and install my new(to me)radar unit in the next few weeks,and plan to give the tach problem a going over at that time.

Quite a few people have told me to move the selector switch on the back of the tach back and forth several times.They claim it's common to get corrosion on the internal contacts at this switch point which causes erratic readings.
I only hope it's that simple.I'll llet you know what I find.

[oldfielder]

wouldn't it be nice if it was just the switch. That seems awful soon for it to get gunked up, though. I had a few issues inside the black shrink tubing at the motor end of a few connectors in the harness that I thought were tight but had come loose inside from getting hit with the boeshield a few too many times.

[Fr. Frank]

Quite a few people have told me to move the selector switch on the back of the tach back and forth several times.They claim it's common to get corrosion on the internal contacts at this switch point which causes erratic readings.
I only hope it's that simple.I'll llet you know what I find.

Use a good electrical contact cleaner just before trying this. If it's a mild film of corrosion, the contact cleaner will break up the surface of the corrosion, and then leave a protective lubricant film behind. I use Radio Shack's "Control/Contact Cleaner and Lubricant", item #64-4315, on electrical cable connectors, switches, potentiometers, etcetera. I then spray the outside with Fluid Film to provide a light moisture/salt barrier.

If you don't use a cleaner, you may just scratch a temporary connection through the corrosion, that will then fail again fairly soon.