[MustardJesus]

It seems when I have the fuse in that powers the gauges, the tachometer jumps to 8,000 (even though the motor idles fine), and the motor will continue to run even when I turn the key off. Any idea what could be causing this?

 

[Ed Brock]

Does it stay at 8.000prm's?
Ed

 

[MustardJesus]

Does it stay at 8.000prm's?
Ed

The Tach does, yes. The engine idles normally though.

 

[Ed Brock]

Dam, that's a problem, as I'm sure you will agree . It sounds like you are feeding power to the coil. But need more info, what year, model, and mods are we dealing with? What have you tried so far? Do you have a spare ignition switch? Have you unpluged the wiring to the ignition switch? When you do does the motor stop running?
Ed

 

[chaseincats]

Isn't the tach gauge needle controlled by a sensor in the spark coil?

 

[MustardJesus]

Dam, that's a problem, as I'm sure you will agree . It sounds like you are feeding power to the coil. But need more info, what year, model, and mods are we dealing with? What have you tried so far? Do you have a spare ignition switch? Have you unpluged the wiring to the ignition switch? When you do does the motor stop running?
Ed

1974 260z. Only mod that I can think of is I hotwired the Emergency switch in the bay to bypass the interlock. All of the smog equipment was deleted by a previous owner. I have tried replacing the alternator, voltage regulator, and I have unplugged the ammeter/fuel gauge as I have heard these are all common fail points. I don't have a spare ignition switch, and I haven't tried anything with it yet. The key on/off works fine when I have the fuse pulled that powers the gauges.

 

[Ed Brock]

I'm guessing your hot wiring is not a new item and all worked normal for some time? Then this problem arised? Correct?
On the back of the tach there is a factory jumper wire if that wire is getting voltage all the time you will get what your systems are. yes cahaseincats is baseitly correct. So, when you shut the key off, do you still have voltage to the coil?
Ed