With GTJoey's help, the car runs well. It was missing very badly until I disconnected the white/black wire from the coil. Now the tach doesn't work. When I reattach the white/black to either the + or - side of the coil, it begins to miss again.

Any advice? Thanks in advance.

Steve near Chicago

 

 

First thought: To reduce some possibilities, hook up black & white wire to coil again and disconnected the black & white wire from back of Tack... this will isolate a bad tach from a shorted B&W wire. From memory there is a capacitor, resistor and possibly a diode within the tach circuitry. Seems like the shorting capacitor was most probable cause of failure (was a common Radio Shack type capacitor). I will try to find tach article with details.

Second thought: the original wire from ignition switch to the coil + side may have been a resistance wire to the old points distributor and coil setup. The new setup electronic distributors, do not like this lower voltage. To see if this is the case, run a jumper wire directly from ignition switch to the coil + if you get improved idle.
If you have the resistance wire, you can replace it with new wire (one size larger), or add a slave relay at the coil, using the original ignition wire to trigger the relay, with direct 12V wire from battery +.

Rgds
David

 

The black/white wire is the old points wire, it should be disconnected. I think the problem here is that the coil polarity has been reversed.

There's no resistance wire used in E-Type ignition systems. Late S2 cars and all S3's had ballast resistors, this isn't relevant to this problem. The 123 is receiving the correct power feed, otherwise the car wouldn't be running.

You can't disconnect the tach wire, because 12V+ is fed to the coil through the tach. Cannot be removed. The coil to tach connection is just a twist of wire around a core..The tach senses current flowing to the coil inductively.