Wired up Tach..But..what the..?!

[Tbuck07]

OK..So I have the standard 5" autometer "autogage" tachometer, and went to wire it up today

Following the wiring diagram, Red to 12V ignition, black to ground, green to tach signal (coil pack on strut tower, negative side..) and of course the white wire I believe to illumination.

However, we hooked it all up just to see if it would work...Theres a little knob on the front of the tach that you can move that will adjust the shift point, and noticed it only works when it has power and ground to it..it wont move if theres no power or ground to it.

However, it wont read a tach signal..Meaning its not showing my RPM's of my motor. I can still turn that knob and once I set it to 6 or 5500 or whatever, itll just stay there at 5500 or 6000. I figured there was a sort of "lock" button to lock it into that shifting point on the tach, then it would simply read the engine's idling RPM's.

Any ideas on what I'm doing wrong..? Or is this tach broken or something??

 

[Paul]

Tach lead is probably hooked up incorrectly. Are you sure you're getting 12v to it? It's four wires, so not a lot can go wrong - check your connections.

 

[ttocs]

you need to test your tach wire. Take your multi meter, set it to AC voltage and tap your wire with one lead(doesn't matter which one) and the other to ground. A good tach wire will show voltage between 2-10v depending on how high the rpms are(higher rpms means higher voltage). If you do not get this(I susped you will not) then check one of the other wires comming out of the coil.

now you are not suprised that it only works when power is on are ya? You sound suprised...

 

[Tbuck07]

now you are not suprised that it only works when power is on are ya? You sound suprised...

What do you mean? I just didnt know that that knob would only turn if given power. Does it have some kind of solenoid that engages a gear inside or something?

 

[HISSIN50]

You could disconnect the tach signal wire you ran (from the neg side of the coil) and put a test light on it. Connect the other end of the test light to 12V and start the car (or just let it turn over if it doesn't start due to other repairs). The test light should flash.