tach not working

[stu]

I'm a brand new owner, just purchased a 1972 240Z, original motor but seller had replaced distributor, alternator and changed 4-speed to 5-speed all from a 1981 280Z. My tach is not working and I was wondering if any of the 280 replacement parts are to blame and what can I do to get the tach working.

[EScanlon]

Hundreds of threads on just this subject. Do a search with your thread title.

In a nutshell, your resistor may be connected to the ignition circuit, but your Tach has been excluded or vice-versas. If it's the resistor that isn't part of the circuit you're potentially burning your points over too much voltage being fed through the coil.

E

[stu]

OK, thanks, I'll do some more searching

[Jetaway]

I'm a brand new owner, just purchased a 1972 240Z, original motor but seller had replaced distributor, alternator and changed 4-speed to 5-speed all from a 1981 280Z. My tach is not working and I was wondering if any of the 280 replacement parts are to blame and what can I do to get the tach working.

Did you buy the car I bought? Oh wait, my alternator is an original type, so it couldn't be. If after researching and tracing wiring diagrams everything appears kosher, suspect a crippled tachometer. It's more than even money that the electolytic capacitaor has given up the ghost. In 1970s audio equipment, they are always #1 on the suspect list for poor or nonoperation. Take them out of air conditioned houses, stick them inside an unventilated can where ambient temperatures can easily range from minus 10 to 130, 140 degrees and let them age 40 years and its a miracle that any tach's from a 1972 still functions. With good luck, the cap quietly slipped away and didn't short out a transistor or puke its corrosive electorlytic onto to other components in its death throes. Replace the cap (+- 20% on the uf, voltage rating equal to or higher than original) and see what happens. If it still doesn't work, suspect the transistors and either test or simply replace. The cap shouldn't be more than $2.00, the two transistors, maybe $6.00 -- $7.00 each at brick and mortar retail.

Good luck!

Chris