Erratic tachomether

[guy48065]

I just went thru this problem 2 weeks ago.
First problem was with a new radio I put in my 25yo freshwater bow rider. The new radio worked for a day, then started freezing on the startup logo, dropping Bluetooth connections, etc. After swapping in another radio the problem returned.
Then my tach joined the 'wonky' party.
I found when I directly connected the radio to the battery--bypassing the fuse block--it worked fine. On close inspection many of the blade fuses had a light film of chalky corrosion on them. I replaced the fuse block, all the fuses, and put new terminals on every wire. The clean power & ground connections fixed everything. Motor seems to run a bit smoother, too.

This flaky power problem did NOT show up on probing with a dmm... Voltage was normal and solid. Voltage drop from battery to radio was just a few millivolts. I got lucky and found I could get the radio to cut out if I gently touched the wire or the fuse for that circuit.
This boat has never been in salt but it's damp a lot and that's enough to cause corrosion.

 

[kd4pbs]

You have to work the seal and metal ring off all the way around the back on the bezel to get it apart. It is a pain, but not impossible. There are probably instructions online or even videos of people doing this. Since you have breaker point ignition, then make sure your condenser is not faulty, the points are clean, and the dwell is set properly.

 

[M0bi0us0ne]

You have to work the seal and metal ring off all the way around the back on the bezel to get it apart. It is a pain, but not impossible. There are probably instructions online or even videos of people doing this. Since you have breaker point ignition, then make sure your condenser is not faulty, the points are clean, and the dwell is set properly.

The ring is plastic, really worried about cracking it

 

[Lou C]

I might want to hook up a voltmeter to your I terminal (Ignition) on the switch and see what voltage it’s getting when the tach acts up. Also some OMCs have high resistance in the charging sense circuit and this can cause overcharging at the battery yet you may see low voltage read out on the dash voltmeter. I had this problem on mine but the tach didn’t act like yours. I’d also try the cyl selector switch and see what that does..