123 Ignition and Distributor Vacuum Issue

[Nicolas Aristodemou]

At the moment the car works fine... smooth idle and revs up very well..... I have driven the car since tgus modification for more than 200 miles .... hope speed relay (connected to coil negative together with 123 ignition black wire) will not be affected.

[Nicolas Aristodemou]

As an update to my previous posts, I have now driven the car over the past month for more than 800 miles (1300km) and it seems to run fine. I have also tried temporarily installing a series resistor of 50 Ohms between the  speed relay (pin 4) and the coil -ve terminal to check operation and the car still runs ok. Maybe I will leave this resistor there permanently to avoid any risk of damaging the speed relay.

[Tyler S]

What is the voltage drop across the resistor? In the original setup with the speed relay hooked to coil positive it would have probably been around 8 volts with the ballast resistor while running. You can check with a volt meter between battery positive and the lead going to the speed relay with the ignition switch on. Keep in mind the 123 shuts off the ground path to the coil when it does not have an RPM signal. 

[Nicolas Aristodemou]

I will check it out Tyler; I had originally tried a 33Ω resistor and measured about 9V; I think with the 47Ω  resistor I should be somewhere between 7.5 - 8.5V, but I didn't actually measure it since I only used the resistor only to check if the car started and revved up normally, which it did. All the mileage I have done was without ballast resistor.

[Tyler S]

Sounds great. You should be just fine then. 👍🏻