Mercury 2000, 75hp 2 stroke Tacho not working

[mctaggart]

Bought a Rib last year and the Tacho has never worked, now that I have been trying to sort out the correct prop size its obviously essential.

However a garage told me the tacho was faulty last year when the boat was being serviced and it was never fixed. So bought a new tacho this week and low and behold the bloody thing still doesnt work. So it seems i have two working Tachos now, argggh!

Anyhow bought this one as a direct replacement

MERCURY 6000 TACHOMETER REV COUNTER | eBay

Needle doesnt move at all be it off, on, or started, set it to the 6 pole setting and wired it up positive, negative and the pulse.

I checked the terminals and they are all corrosion free, can someone offer advice on checking the obvious. Will test there is 12v tomorrow, but if its got a healthy power supply what else do i need to check.

My battery is being charged also while the engine is running as the voltage increases on my fish finder display, as i know that could point to another problem on the merc with a tacho not working.

Help!

[uncle al]

the grey wire from your regulater is the tach impulse wire,but check the plug and socket connection by the control box first

[9D280]

Do you have a digital multimeter? If not go & spend a fiver on one......

Then you should see;

12V between the earth & the "not grey" wire.

Then set the meter to AC & you should get around 5-ish V between earth & grey, rising with revs but not much.

(It's 5-ish V 'coz the meter expects to see a "clean" 50Hz wave. The alternator sends out 12V pulses at varying frequency which basically confuses the electronics a bit, but it averages out at about 5&a bitV on a digital meter.)

[mctaggart]

Had a nice day to work on the boat today, with my Tacho gauge being on my list of to-do things. I checked the continuity on the signal wire up to the block connector on the engine and it was dead, so that was good i thought. At least its just a defective wire/connection. Followed the wiring back up to the console and low and behold i found another connector which went to the throttle unit etc and some ominous red electrical tape hidden away.

Turns out some wally had cut the bloody signal wire, why i have no idea but at least its fixed

So multimeter worked a treat

onto the next task, of which is as long as my arm!