'85 analog tach connections, testing

[bdwernychuk]

I'm still trying to get the the tach to work on my '85.

Does anyone know how to test the tach itself? Here's what I can tell you so far:

The ground to the instrument is good and with the engine at idle I'm seeing just under 6v DC and 12vAC according to my multimeter. I have no clue if this is good, bad or meaningless, all it tells me is that I have continuity on the green (signal) wire between the instrument and the engine.

On the back of the unit there is a ground connection and a signal connection. The signal connection has 3 posts like this:

12 B 4

The green wire connects to B and a jumper connects B to 12 on my unit. Can anyone tell me what the "12" and "4" mean? As this thing doesn't work anyway, I'm tempted to switch the jumper to "4" but hesitate lest I do some damage to the engine.

BDD

[bdwernychuk]

OK, I'm replying to my own message ...

The 12v AC on the green tach wire is right, given that the green wire comes off the unrectified side of the alternator, so this meant the tach was dead. A quick trip to the local chandler for a universal Faria tach and the problem has been solved.

[Ken]

BDD,
Thanks for sharing your solution with us on the tach problem - I've had no experience on that tach, but I would guess the two connections on the back for the jumper would accomodate different alternators on different motors - some would give you more "ripple" from the ac signal than others for one revolution of the flywheel, depending on the number of coils in the stator that make up the alternator.
Good luck,
Ken K