Tachometer wiring questions

[dan juhasz]

I’m working on the 67 RT. Car is an automatic. Tach is not working, I only have the Plymouth service manual but I’m thinking it’s the same. When I look at the schematic it shows auto/console/tach hook green lead to positive coil. Next schematic manual/console/tach hook green to negative coil. I tried both ways nothing. I also am not sure what I should be looking for on the violet wire going into tach, is it voltage or ground?
Need help, thanks Dan

 

[MoparMitch]

I’m working on the 67 RT. Car is an automatic. Tach is not working, I only have the Plymouth service manual but I’m thinking it’s the same. When I look at the schematic it shows auto/console/tach hook green lead to positive coil. Next schematic manual/console/tach hook green to negative coil. I tried both ways nothing. I also am not sure what I should be looking for on the violet wire going into tach, is it voltage or ground?
Need help, thanks Dan

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Dan, I'm pretty sure that on the 67 and earlier cars with Tachometer, there is a sending unit mounted in the console or under dash. Do you have the sending unit ? Later years had the sender incorporated into the Tachometer....

 

[AR67GTX]

I believe it always goes to neg on the coil - the distributor side.

I also think the sending unit was incorporated into the tach for 1967 - unless I’m remembering wrong. Of course those tachs have been swapped around and exchanged over the years.

 

[R413]

Tech senders are used on 1966 and older. 3 wire tach
1967 tach doesn’t need it, 4 wire tach

A tach wire always goes to the negative side of the coil.
It wont get a signal from the positive side.

where did that book come from that shows + side?

 

[dan juhasz]

Tech senders are used on 1966 and older. 3 wire tach
1967 tach doesn’t need it, 4 wire tach

A tach wire always goes to the negative side of the coil.
It wont get a signal from the positive side.

where did that book come from that shows + side?

67 Plymouth service manual.

 

[dan juhasz]

Problem resolved. I was missing the positive feed to the violet wire to tach. I didn’t know what circuit powered it. I called the guy who made the harnesses to incorporate the factory tach. That wire gets it power from the reverse lamp switch, it has a splice a few inches back in the harness. Problem was it was spliced into the output to the reverse lamps after the switch. So the tach only worked when the car was in reverse and I never noticed it. Who looks at their tach in reverse? I cut the lead and spliced it into the other lead that is always hot key on. Works fine now.

 

[R413]

If you look in the 1967 Plymouth Service Manual it has automatic Trans with tach with green wire to negative side of coil. Next to that is another diagram for manual trans with tach and it shows the green to negative side of coil. LOL

 

[dan juhasz]

If you look in the 1967 Plymouth Service Manual it has automatic Trans with tach with green wire to negative side of coil. Next to that is another diagram for manual trans with tach and it shows the green to negative side of coil. LOL

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It had me scratching my head.

 

[69L48Z27]

My 67 FSM is the same. Auto shows positive coil connection also.

 

[Ron H]

Good point Dan! Don't think I've ever looked at my tach in reverse, lol

 

[Geoff 2]

No, not all tachs connect to the coil [-] wire. Current triggered tachs connect to coil [+] .