• When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.

Which is my wire for factory tach on firewall? 74 Roadrunner with A/C

Lineman

Well-Known Member
Local time
12:28 AM
Joined
Jun 24, 2017
Messages
145
Reaction score
30
Location
Glen Burnie, MD
Thanks for the help, I am trying to reconnect my factory Tach. Its a Factory A/C car and there is what looks like a dark green wire with the by the heater fan connector/s that is cut clear. Could that be it? There is another brown wire coming thru the firewall closer by the brake booster cut clear I don't know what that is for either?

Any and all help appreciated.

Thanks
Jay
 
Thanks for the help, I am trying to reconnect my factory Tach. Its a Factory A/C car and there is what looks like a dark green wire with the by the heater fan connector/s that is cut clear. Could that be it? There is another brown wire coming thru the firewall closer by the brake booster cut clear I don't know what that is for either?

Any and all help appreciated.

Thanks
Jay

There is a brown wire that comes off of the spade connector on the back of the tack.... it goes through a grommet on the firewall that should go to the neg. of the coil.
Jeff-
 
On 74 the tach wire runs throught the NSS bulkhead harness plug. The only cavity free there ( or if present, the only wire not tapped with the rest of the NSS harness ). A/C harness runs throught the firewall with grommet

On 71 tach wire runs throught the engine harness bulkhead plug. A/C harness uses the two NSS plug free cavities ( On 71 the NSS grund signal wasn't needed into the cab like 72/74 do )

72/73 tach wire runs with a grommet throught the firewall. A/C harness wires were shared between engine harness ( clutch ) and NSS harness plug ( blower )
 
Last edited:
Thanks to everybody on the thread. It was the brown single wire coming thru the firewall.. I looked under the dash and I looks like there it is a grey wire with a black tracer (I think it was) but somehow it must have changed at the firewall to the brown wire in the engine compartment...

But now the factory tach works and I am back to factory ignition with the MSD 6A in a box with the distributor.. I don't know if the MSD stuff is worth keeping around or not. The car sure seems to run nice now.. And if I have issues on the road someplace this system should be much more serviceable on the fly..

Thanks again for the help..

Jay
 
Auto Transport Service
Back
Top