1990 Z32 N/A Tachometer Not Working

[frootiebootie]

So I bought a 1990 300zx N/A 2+0, and before we closed the guy told me that the tach was not working. Being way too excited about owning my dream car to give a sh*t, I bought it anyway. Now, after the fact I realized that I am terrible when it comes to circuit work. SO looking for some help to see if anyone knows what could be causing the issue. The tach itself has been at zero since I bought it. It has not moved at all. I took the dash apart and I tested pins on the wire that connects behind the tach. According to the service manual, the tach wire is connected to the oil pressure sending unit. I tested the wire and there is no current through the 22/23 pins on the wire (the wires that are referenced in the manual as being for the tach). So right away I see that the tach wires are not getting any current, which means that the unit is likely functioning. Any ideas on what could be causing it? Does anyone know exactly where the tach is wired and how it functions on this particular car? Crank sensor? Speed sensor? How would I go about fixing the tach? Thanks in advance!

[rgregoryb]

Actually it is not connected to the oil sending unit. It received its input from the ecu. It is different for auto or manual trans. Google "eccs-color.gif for 1990 300zx" it's much easier to follow the wiring diagram. If it turns out the tach is bad I have one for a 1990 you can have.

[rgregoryb]

Check the fuses?

[frootiebootie]

I followed the wiring diagram, that's how I got the sending unit idea. I googled the color code, looks like pin number 7. I guess I should test the 7th pin then. If that 7th pin isn't getting power, do you know what else could be the problem? Checked the meter fuse in the driverside foot well, it's fine. I'll let you know if I need a tach though, thanks.

[rgregoryb]

The initial signal is from the crank angle sensor to the power transistor unit to the ecu then to the tach. These cars are well known for electrical connections becoming corroded. I would start cleaning the contacts and be careful the connectors sometimes break by looking at them too hard. Get a can of electrical contact cleaner, it will become a necessity.

[rgregoryb]

If you Google "where does the signal for the tach come from on a 300zx" there is a discussion at Improved Touring about installing an after market tach and it tells you where to look for the signal. I tried to copy the link but this tablet sucks at that.

[frootiebootie]

Dude you're honestly just a bad a**, in case you weren't aware. Thanks a bunch for the info, this tach issue has been bugging me. So I should check the ECU, power transistor unit, and crank angel sensor connections. Be sure not to look at them while I do. I took a look at that forum, and it gave some decent info as to the wiring situation and the color of the wire etc. I'll be taking a look tomorrow, since I'm gonna take the dash out again to replace the LED's. Doing some red ones. My multimeter isn't available right now so I won't be doing any wire testing, but I can at least take a look at the contacts.

[rgregoryb]

We have to work together to keep these beautiful cars going.