Tach is going crazy!!! Help

[Rob1000]

I put a sunpro tach on my 72 cheyenne, and whenever i turn on the fan or headlights or anything electrical, my tach starts going crazy. I have a mallory distributor with the green wire hooked up to it. I have it grounded to the battery, which is better than grounding it under the dash where it was. Any suggestions would be appreciated.

[rage'nrat638]

you have a seprate 12 volt wire running the dizzy from a keyed 12 volts on the fuse box?

the old voltage wire is a resistor wire.. does not supply full 12 volts..just a fyi

sounds like your getting voltage spikes.

i have mine grounded to the dash frame.

[72chevy327]

? the wires sound right are you sure its set on v8 on the tach, i don't think thats it but its worth a look. thats all i can think of.

[Shyguy]

I put a Sun tac in my 71 C-10 today also and it seems to work ok.

I hooked the ground wire under the dash.

I guess I was lucky the previous owner had installed a new wire when the Hei distributor was put in, I think it is a late 70's stock distributor.

Danny - SEMO

[matthufham]

my tach goes crazy too. it's an equus gauge from o reilys. i have 4 of those brand gauges and a tach but only the tach seems crazy. it constanly goes to 0 then works and sometimes stays on 0

[Rob1000]

It was grounded to the dash frame, so i grounded it to the battery and now it only does it when i turn on something electric. Before it did it all the time. I'm gonna look for that power supply in the fuse box you were talking about.

[rage'nrat638]

Originally Posted by Rob1000

It was grounded to the dash frame, so i grounded it to the battery and now it only does it when i turn on something electric. Before it did it all the time. I'm gonna look for that power supply in the fuse box you were talking about.

yes it needs a new wire ran for the hei.a nice 16 gauge or 14 gauge would be best.

the old original resistor wire don't supply full 12 volts so the points did not burn up...

[corn]

Unhook the wire to the dizzy & then see if it goes wild when turning other stuff on. That should help you decide if its the dizzy lead or the 12v lead. Is the distributor an HEI style or a remote coil type? The tach lead needs to be on the -side of the coil or the tach post on an HEI style...

[Rob1000]

My distributor doesn't have a remote coil. I'll try running a 14 or 16 gauge wire to the distributor. Oh yea what's a dizzy. thanks

[corn]

Originally Posted by Rob1000

My distributor doesn't have a remote coil. I'll try running a 14 or 16 gauge wire to the distributor. Oh yea what's a dizzy. thanks

its just a lazy mans way of typing distributor.

[Rob1000]

Thanks for the help. Hopefully it will fix my problem.