Tach Hookup Instructions from Nisonger

[Patrick67BJ8]

I got the Tach all hooked up and fired up the engine, Tach shows 1000 RPM but when I rev the engine it drops off to zero. I double checked all connections and they appear to be good. The Tach before I had it rebuilt would go to about 2700 rpm before it dropped off to zero but the longer I drove the car the Tach would actually increase in RPM's shown on it. Peter at Nisonger said that it may have worked good when I first installed the Pertronix but it got worse the more I drove the car. The Tach worked great before I did the frame-up restoration. Photos of the coil connections. There's 3 wires on the Neg side of the coil, the old original white wire, the new white wire that I just ran to the white wire coming out of the Tach and the Red wire for the Pertronix.

On a possible related note: When I did all new wiring I was told to not use the white/black striped wire and to leave it disconnected which I used a couple of tie straps to tie it against the wire bundle.

 

[Patrick67BJ8]

On a possible related note: When I did all new wiring I was told to not use the white/black striped wire and to leave it disconnected which I used a couple of tie straps to tie it against the wire bundle.

Another beer and I fixed it!

The Red wire that comes from the Dizzy/Pertronix to the Coil goes to the + terminal of the coil.
The OLD Tach White wire goes to the + terminal of the coil.

The NEW Tach White wire goes to the - side of the coil terminal.
The Black wire that comes from the Dizzy/Pertronix to the coil goes to the - terminal of the coil.

Looks like I had originally hooked it all up bass-ackwards.

 

[dklawson]

There's 3 wires on the Neg side of the coil,
the old original white wire,
the new white wire that I just ran to the white wire coming out of the Tach and the
Red wire for the Pertronix.

In post #1 you said the car had been converted to negative ground. Your wiring above is not consistent with negative ground wiring.

Forget the tach for a moment and look at just the coil wiring. For negative ground you want a white wire coming from the ignition switch going to coil (+). The coil (-) terminal will have a wire going to the distributor. Since you have a Pertronix unit, its black wire will be on coil (-), its red wire will connect to coil (+) along with the white wire from the ignition switch.

On your converted tach, the insulated terminal on the back connects to a switched, fused circuit (a green wire circuit behind the dash or at the fuse box). If you don't want fused power, you can connect the insulated tach terminal to coil (+).
The case of the converted tach requires a ground connection to the car's body.
Finally, the new white wire on the back of your tach gets extended and connected to coil (-) along with the Pertronix black wire. If possible, use white/black wire to extend the tach wire. White/black is the correct color code for wires attached to the distributor side of the coil.

When a car is converted to negative ground, the coil connections are supposed to switch. On old coils marked SW and CB, the CB now gets connected to the supply voltage and SW gets connected to the distributor. On modern coils, the terminal marked (+) or 15 will receive power from the ignition switch, the terminal marked (-) or 1 is connected to the distributor. The coil will work wired "wrong" it will just have a weaker spark.

 

[Patrick67BJ8]

In post #1 you said the car had been converted to negative ground. Your wiring above is not consistent with negative ground wiring.

Forget the tach for a moment and look at just the coil wiring. For negative ground you want a white wire coming from the ignition switch going to coil (+). The coil (-) terminal will have a wire going to the distributor. Since you have a Pertronix unit, its black wire will be on coil (-), its red wire will connect to coil (+) along with the white wire from the ignition switch.

On your converted tach, the insulated terminal on the back connects to a switched, fused circuit (a green wire circuit behind the dash or at the fuse box). If you don't want fused power, you can connect the insulated tach terminal to coil (+).
The case of the converted tach requires a ground connection to the car's body.
Finally, the new white wire on the back of your tach gets extended and connected to coil (-) along with the Pertronix black wire. If possible, use white/black wire to extend the tach wire. White/black is the correct color code for wires attached to the distributor side of the coil.

When a car is converted to negative ground, the coil connections are supposed to switch. On old coils marked SW and CB, the CB now gets connected to the supply voltage and SW gets connected to the distributor. On modern coils, the terminal marked (+) or 15 will receive power from the ignition switch, the terminal marked (-) or 1 is connected to the distributor. The coil will work wired "wrong" it will just have a weaker spark.

I removed those 3 white wires on the coil terminal once I figured they were wrong. The wires on the back of the Tach are correct. The green wire is fused to the fuseblock and the new white wire coming out of the Tach is going to the Neg terminal on the coil along with the black pertronix wire. I have ground wires on both the threaded studs on the Tach which are black and also connect o the other instruments and chassis ground. The car was running, but the Tach wasn't getting proper signal because it was on the wrong terminal on the coil. I believe when I hooked the wires originally up I was given the wrong instructions. All seems to be good now.