tach wire signal voltage?

[crucial118]

Whatup? I have an efi'd 406 sbc with the small distributor, and external coil. The other day the my tach stopped working. I thought it was the tach, so I had a Sunpro sitting around, and I installed it. Same thing, It lights up, but no needle movement. I thought the wire might be cut or something, so I pulled a new wire from the tach to the gray connector white wire, and still nothing. The question I have is what sends the signal to the tach wire? Is it 12v or is a ground? Bad distributor? I have installed a new ign control module, coil, cap, rotor, wires, and plugs. Under the rotor, there is a little surface rust, but I don't think it is that bad too warrant a new distributor tho. Any help would be appreciated, I'm stumpped.

 

[crucial118]

Re: tach wire not giving signal

For real, no one knows? I have 11.6v on the tach wire with ign on, engine not running. Does that mean the tach is bad? All ignition systems should be the same, since the same tach can be used for multiple cars, right?

 

[Longroof79]

Re: tach wire not giving signal

You mentioned the "small distributor". Is it an MSD unit, or an older style points distributor converted to electronic, like a Pertronix?
Where does your current tach wire go? I know on an HEI it goes right to the tach terminal on the distributor. On one of my older cars that had a points distributor with an external coil, the tach wire went to a terminal on the coil

 

[crucial118]

Re: tach wire not giving signal

You mentioned the "small distributor". Is it an MSD unit, or an older style points distributor converted to electronic, like a Pertronix?
Where does your current tach wire go? I know on an HEI it goes right to the tach terminal on the distributor. On one of my older cars that had a points distributor with an external coil, the tach wire went to a terminal on the coil

It's the distributor off a 91 camaro. Electronic. My current tach wire goes to a remote coil, like on this diagram.

 

[crucial118]

Re: tach wire not giving signal

Some more pics and diagrams of what I'm talking about...http://www.google.com/search?q=tpi+remo ... 1&imgdii=_. Hit web, then image and you'll see.

 

[crucial118]

Got it fixed. Luck of the draw...2 bad tachs. Borrowed 1 from a friend and his fired right up. Thanks anyhow Longroof. Found the answer to my question also. The distributor sends out pulses of 12v that the tach translates to rpm(best I could figure).