tach issue

where on the firewall harness would the tach wire be located?

Depends on which car and year.

its a 70 challenger r/t

Info I have states that the tach wire is seperate. It should be an 18ga gray wire with a tracer that goes thru a grommet in the firewall. This would be true for all engines except the Hemi.

that how I thought it was too

Looking at some old engineering drawings that I have. If the tach did go to the connector it would be in pin #20.

thanx for the info, ill look into your suggestions. in the meantime, anyone know why the tach needle would go straight to the top when the key is on and after it starts?, ive removed the wires to the coil and the alt, and it does the same thing. thanx

sounds like you have the tach hooked up to 12v. better check it with a meter

you might jump the tach wire directly to the coil neg, start the eng & see if the tach itself is good.

ill definetely try that, thanx.
i notice that there is a pos and a neg wires connected to the alt gauge, and thats what seems to power up the complete dash cluster. anyone know if this is correct? appreciate all your help guys! this one has got me stumped

Yes, in a rallye dash like on my A body, the
wires go directly to the amp gauge and basically power out from there.