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MG MGB Technical - Where does this wire go?

Have a 74.5 MGBGT and am installing an electrtonic ignition. There's a black wire which attached to the dizzy from the harness bundle. I have the red and blach wire from the dizzy and electronic ignition connected to the appropriate coil terminals. What do I do with that one blck wire?? Any ideas??? Thanks! JOHN
JW Colson

Are you installing a pertronix ignitor unit? If so, the black wire from the unit goes to the - terminal on the coil, the red goes to the + terminal on the coil. See http://www.pertronix.com/downloads/ignitor12vneg.pdf for further directions.

HTH, Erick
Erick Vesterback

John. I assume that you are running the original Lucas 25D4 distributor. If so, there was no black wire from the harness connected to it. The wire ran from the output terminal of the coil to the connection on the side of the distributor to the points. The points grounded through the base plate which his attached to the distributor body by a wire.

Hence, it would be useful to know what your original distributor is, whether you are replacing the entire distributor or just the points, and what replacement system you are using.

Les
Les Bengtson

Les, you are correct. I am staying with the 25D4 dist. The wire I am addressinbg is the black and white one which connected to the distributor from a bundle of wires from the harness. The red and black wires from the electronic system come from the area where I once had this black and white wire connected. I am using the petronix system. It has two wires coming from the distributor which are connected to the positive (red) and negative (Black)which are connected to the coil. John
JW Colson

Sorry John - I didn't read your initial post correctly. I wonder if the black wire you refer to is actually a white wire with a black stripe. The same wire on my car was black from dirt before I detailed the engine bay years ago. Normally there is only a solid white wire from the ignition, and a pair of white wires with a black stripe on each - one from the dizzy, and the other leading to the tachometer. From what I gather from the instruction page the white wire with the black stripe which originally goes from the dizzy to the coil, is not connected, and the red wire from the pertronix goes to the coil in its place. The other white/black wire still needs to be connected to feed the tach its signal. I think that the black wire from the pertronix goes to the white/black side of the coil ie -ve, and the red to the same side of the coil with the solid white wire ie +ve. If I am wrong, I'll be interested in the correct wiring, because I am about to make this same conversion in the next couple of days. Just got the engine back into the car after fixing an overdrive leak, but nothing done past doing up the engine/transmission mounting nuts. I had Jeff Schlemmer build me a recurved dizzy with pertronix (will keep the entire original dizzy in the trunk in case of sudden failture of the pertronix). From what I understand, these units are sensitive, so we don't want to connect it incorrectly and fry them...

Erick
Erick Vesterback

John. Erick is correct. The wire coming out of the harness goes to the tach and needs to be hooked up to the coil for the tach to work.

Les
Les Bengtson

The white/black goes back on the coil -ve, which should be where the black from the Pertronix goes.

A North American 74.5 i.e. a rubber bumper should originally have had a 45D4, not a 25D4. It should also have the ballasted ignition system and the 6v coil, which means you may have to run a 12v feed to the Pertronix red to get it to work properly instead of running it off the coil +ve, which switches between 12v and 6v.
Paul Hunt 2

Thanks, guys. This has been helpful. I will be connecting the white /black lead from the harness to the neg on the coil. By the way, I too had jeff rebuild my dizzy. He was very good to work with and I am excited to finally get this sweetheart working. JOHN
JW Colson

This thread was discussed on 01/05/2007

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