1978 MG Midget with Points Distributor

[TomR]

I recently purchased a 1978 MG Midget that the previous owner replaced the electronic distributor with a points distributor. It appears that he used whatever wire he could find anf stuck it in the female plug in the wiring harness. I've tried to figure out which wires run from the from the coil to wiring harness and cannot find a schemactic that illustrates which wire go where and would appreciate any information or source of a schematic that I could use to finish up the repairs to the electrical system. TIA

 

[dklawson]

I do not know which "original" wires would be appropriate. Surely the electronic distributor woud have a 12V switched feed to the electronic module. If you can determine which one that is, connect it to coil (+). Depending on which distributor the PO installed you will also need to either run a wire from the terminal on the side of the distributor to coil (-) OR you will need to connect the wire exiting the side of the distributor to coil (-).

In the general Lucas wiring scheme, power to a "standard coil" ignition system with points utilizes a white wire from the igntion switch to coil (+) and a white/black wire between coil (-) and the distributor. If your car's PO installed a ballast ignition system (unlikely) there are a couple of changes to this.

 

[Guest]

I do not know which "original" wires would be appropriate. Surely the electronic distributor woud have a 12V switched feed to the electronic module. .

I thought that too but from what I found that's not correct. It's a resistor wire that only feeds 9v or so IIRC. I don't know why, it's a GM 4 pin module in the black box which was designed to run on 12v. I've been tempted to run straight 12v to it but I'm afraid of cooking my dizzy....it is a Lucas unit after all. Tom, I'll have to check my '79 and see.

 

[dklawson]

So they ran the "pink" wire to it? That sounds like what they did with the late 1500 Spitfire. Yuck. That does change things.

Tom, before offering any further comments, do you have access to a multimeter to measure the coil resistance or do you know what type of coil you have?

 

[dklawson]

I don't know whether the document linked below is subject to copyright. Regardless, online I found the following:
https://www.spridgetguru.com/78MidgetWiring/78MidgetWiring.pdf

Early in the document (Page 6?) is the overall wiring schematic for the 78/79 Midget. The coil, distributor, and other ignition parts are shown in the bottom left corner.

Note that the coil (+) terminal is fed by a pair of white/light-green (WLG) wires. One WLG wire has a resistor in it, the other goes to the starter solenoid. Though the color codes are different than used on earlier cars, that scheme is typical of ballast coils.

Before advising you what is right and what will work we need to know what coil is on your car. Please mark and disconnect the low tension wires from your coil, measure the resistance across the low tension coil terminals, then tell us what value you found. Once we know the coil resistance we can offer comments and suggestions on how and where to wire your points type distributor.