1987 XJ-S V12

Tach seems to have died.

Polking around the web, it doesn't seem that there is an easy way to test it. Of course maybe *today's* tachs are more sophisticated than those of 1987.

I feel I need to test two things, the signal coming from the ignition amp, and the tach itself, to nail down the problem.

Any suggestions?

Thanks,

John

 

Besides the signal from the ignition amp the tach also needs 12 volt "key on" power and needs a ground. Any or all of the three might be compromised by poor contacts at the cluster connector or printed circuit. Problems here are common, as we know

If all three are OK then the problem can only be the tach itself

Testing is easy in theory; simple test light or meter will suffice. Access gets a little tricky

Cheers
DD

 

Doug,

Should have been more detailed in my post. Tach has continuity to ground and is getting +12 at the proper terminals.

There is no more printed circuit in mine. I'm in the process or hard wiring everything. All the instruments are done, and work as expected, except the tach. Since I did nothing to it (didn't even dismount it from the instrument housing) I'm confused why it worked before, but doesn't now. Then again, this won't be the first time something broke because I looked at it wrong.

Given the price of a "new" one, I just want to make sure I'm getting the proper signal from the ignition amp. Do you know how I can test that?

Thanks,

John

 

A multimeter on AC volts can be used to verify the tach signal. Don't know what voltage you should expect but I would guess a few volts. If the meter has Hz function even better, the frequency should go up as you rev the engine.