Tach signal source

[Larry1942]

Previous owner told me that when the on again off again tach finally quit, buy a new one. After trying unsuccessfully to restore operation or find the signal source of Tach signal on my 1984 27 FC with a lehman marinized peugeot 4d61, I bought another tach and wired as per instructions. Unfortunately that didn't solve the problem either. Perhaps the signal is not from the alternator. Any help out there?

[don123]

I don't have my 4D61 anymore so I can't go look to double check, but I believe the tach is fed a signal from a sensor which counts the teeth on the flywheel used by the starter. Check the bellhousing area for a screw in sensor with two wires

Since your tach was intermittent for a period before it quit altogether, I would check the wiring between the engine and the instrument panel. You've eliminated the tach as the problem, it must be either a bad sensor or a wiring problem

Hope this helps,

Don

[jleonard]

Or a sensor out of adjustment. Probably screw I till it touches then back off a turn and a half.

[Don from Mystic]

The tach on my 1983 is alternator fed. It is a Motorola alternator. I believe the tach lead is gray coming off the alternator (It is shown on wiring diagrams for the 4d61). This topic was discussed a few years ago by "Fortunate" who replaced her tach with an aftermarket. If I recall correctly she had to set the switch (maybe a dip sw) to sync with the alternator.

[denchen]

I took the signal off my conventional car alternator by connecting a single wire to one of the main wiring coils in the alternator before the rectifier. As added safety I put a 1 amp fuse as the wire comes out of the back of the alternator. The tach works a treat.

[Larry1942]

Thanks all. Mystery solved.

[N4QC]

And the solution to the mystery was....

Nice researching,