Tach only works on startup

[Blazer85]

Hello,
Today I tried to install an autometer 2300 tach in my 168 roadrunner. I hooked it up and on startup it would work but as soon as I stopped craning it would not work. It is always lighting up with the key on, any ideas where the issue is?

 

[A383Wing]

you got the power wire hooked to wrong side of ballast??

where are you taking 12v key on power from?

 

[Blazer85]

I am getting the 12v power directly off the positive line from the ignition switch.

 

[Meep-Meep]

You are puling 12V from the crank position rather then the run position. Find a fuse in the fuse box that shows 12V with key on.

 

[A383Wing]

yea..basically what I was getting at, he's got 12v from wrong power source...my fingers are stoopid sometimes

 

[HT413]

Wow, I have to say, you sure picked an unlucky wire, not a lot of wires in the car that are only hot in the crank position. A piece of advice, when picking the fuse position in the fuse box to take power from, turn the dash lights on, but dim them about half way. This way when you check voltage, that circuit will show something like 4 to 8 volts or so. This way you won't accidentally use that circuit.