No tachometer

I guess too many breakers is better than none. Quite a rat's nest.

If your tach really is inoperative and you take off the face of the tach (difficult to do without breaking something and there are NO individual parts available), inside you'll find a matchbox sized printed circuit board screwed down, with precision 1% value glass resistors soldered on. After 50 years, a resistor may crack, which opens the circuit. You may need a strong magnifying lens to see the crack. Desolder and it will confirm its condition by falling in two pieces no matter how careful you are. Replace the resistor with its exact 1% value. If you're lucky, thats all thats wrong.

Note- Even if you use precision grade 1% resistors with the exact same color code, this will likely still change the calibration of the meter slightly, so electrical recalibration may be necessary.  Some of the other components are electrically  'trimmable'. Then reassemble the tach again without cracking or denting the plating on the chrome face-surround.

So bottom line, unless you are a trained electronics tech,  you may be better off to just replace the tach entirely. They have never been cheap.  All this is why few 'speedo rebuild' shops actually do more than clean the face of a Veglia tach during their refurbishing (not really a rebuild). All known tachs in DeTomaso cars are the same- Pantera, Mangusta, Longchamp, etc. Not sure about other brands but a broken tach has some value so don't throw it in the trash. Good luck.

Without an ignition box, the Pantera's tach connects to the negative coil terminal. No tach adapter is needed.

The blue wire or the black wire (not both) connect to the negative coil terminal. The blue wire is used if the FiTech is NOT controlling the ignition timing.  The black wire is used IF the FiTech is controlling the ignition timing, and the distributor's advance MUST be locked out.

Check with Jon Haas (Pantera Electronics) about repairing the tach.

John

https://

@larryw posted:

Is there a way to bench test a tach?

I never got a chance to verify my notes actually worked and hate to cause damage to someone elses . . .  But here is youtube of bench testing tachometers.

In leu of the "transformer" of unknown ratio, I've heard a battery charger provides the wave form to trigger the tach.

However.   I haven't done this myself and don't think I could "anlysis" any more

youtu.be/oVCOA5MX81I?t=141

Agree with John, iIts probably only the issue of the electronic ignition; if you have a distributor with simple points and connect the Veglia tach to the coil, it probably will trigger. The Veglia tach itself is fantastically common. They are neither precision devices, as I can tell the differences between application on 4 or 8 cylinder are rotation of a trim pot. Opening the speedo/tach are actually easy (completely different ballgame from the 2" gauges)...which probably explains why bezels are completely unavailable for the big gauges.

  A "Tach Amp" can splice the difference between a digital trigger (which I suppose the EFI unit outputs) and the Veglia. Suggest this as a cheap start  https://www.ebay.de/itm/142171581596   

Battery charger idea in the video too easy not to try. I thought the tach needed a square wave signal to trigger, but evidently not. TY. Will advise.

...newer tachs will fire off almost anything, but the Veglia tachs need that kick off the coil. Fiat 124 tachs are easy to come by and even, a direct swap into the DeT can in the even yours is really broken...Lee

It turns out that whomever reinstalled the tach after the interior was reupholstered put the tach hot wire on the signal terminal and vice-versa.

Reversing the wires provided no joy. Too late I guess, damage done.

Testing using another tach confirms this one is NG.

...a whole replacement DeT tach is not hard--they come up all the time at about $200. If you want this one repaired, Bosswrench is correct that a place like Palo Alto speed can do it for about twice that. If you want to move the movement from one working tach (even a Fiat 124 tach you can buy for as low as $20), you still will want some way to move the needle to the right place (calibrate against another tach).

The assumption is that the tach is really bad--honestly, connecting the +12 to the tach input won't kill it (it is isolated by a resistor and cap on the input, so really no current will flow). So if the other tach you've measured the circuit against is another 60/70's Veglia tach, OK, the other may be bad--but any other $15 modern tach from Hong Kong will switch off a low voltage square wave. (the Veglia will not)--Lee

I swapped the questionable tach with known good pantera tach from a running car. It worked.
The questionable tach failed to work in the pantera I borrowed the good tach from.
The bad one is going to Jon Haas for repairs.