Big Mikey

Hey guys I got a weird one here, the po put in custom gauges in the original location of the dash of my 68 Cutlass and I just went through and tried to fix all that was wrong with the wiring....and it was a mess!!! Everything seems to work fine until I turn on the headlights and light up the gauges-the stupid tach needle freezes and will not move until I turn the lights off. I don't think it would be the ground, maybe I crossed the light terminal with the feed??? But would that power the tach??? Some great ideas would really go a long way-thanks again!!! I really don't wanna take the stupid dash apart again!!!-I just got it put back together.....

oldcutlass

You can google the wiring instructions for your model tach, then verify.

Lady72nRob71

Do check the grounds to make sure the tach is grounded well.
The tach I put in my Ford long ago does a similar thing - the needle drops instead. I should check the grounds on it also.

Big Mikey

Anybody with good advice?? It has blade type connectors on the back for 12v, ground, feed and lights....I swear I hooked them up correctly, but I am a little lost here on why it would freeze when the lights come on...

joe_padavano

X2 on the ground problem. Sounds like either you have the lights hooked up to the ground or the ground wire is not connected properly. Sounds like a similar problem to when the parking light socket is not grounded properly and the turn signal filament grounds through the parking light circuit.

Big Mikey

Seperate ground bundle for gauges only going straight to the firewall, and the lights are from the harness. So I can't see where I crossed them, but if could the feed and 12v be crossed?? Would the tach even work then?? I am sure this is something fairly simple-just really weird one that has me baffled!!!

oldcutlass

Is it wired like this?

Big Mikey

Well sort of it has blades on the back of it and I had to use crimp ons, but essentially it's the same thing. I thought I was careful to wire it proper, and can't understand why switching on the lights would cause the tach to freeze....the lights are all bundled together and this is the only gauge without a push in light, it's back lit. I don't know if the po messed up and when he wired it crossed the wires and blew out something or I crossed a wire.... Honestly really confused on this one!!!

oldcutlass

Have you tried disconnecting the light wire to see what happens?