I'm getting ready to install my motor and I'll be putting a MSD on when i do that. My car is already equipped with electronic ignition. What did you guys do with the wires and large plug that went to the original electronic ignition?

You can remove the ECU and ballast Resistor, or just disconnect them and leave them in place as a backup ignition should the MSD ever go belly up for some reason (unlikely).

The two wires from your ignition switch leading to the ballast resistor connect to the MSD's small gauge red wire.

Green and purple to dist pickup.

Orange and black (small gauge) to coil.

Heavy gauge Red and Black to battery.

White wire is not used.

-S/6

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The "Silver Bullet"
87 Ram D150

I believe that I understand how the MSD hooks up. What I'm wondering is what to do with the wires that ran to the old ECU. I don't really want to cut them, but i dont want that plug just hanging there, so I was curious as to what others had done.

When you short the two ign. wires to the single red MSD input wire, don't you end up w/ power to ACC while cranking? I've been told that that can be hard on amps, etc. Wouldn't it be better to use a diode or two for isolation?

I've installed two MSD's that way on two seperate ('78 and an '83, both small blocks) dodge trucks. The owners have never conveyed any problems to me.

Here is what I *think* happens, since only one of the two wires has power at a time. Yes, the 'start' wire will back-feed the "run" wire during cranking (and visa-versa), but the backfeeding stops at the ignition switch. Why? Because if there is no contact being made to provide the 'dead' wire with power, then there is nowhere for power that is back-feeding to go past the ignition switch.

That is how it seems to work in my mind. If I am way off base someone please correct me. But I have had no problems with simply connecting the wires.

'73 - Your options are to (1) remove the ECU, ballast resistor, and the associated wiring no longer being used, or (2) leave everything in place, with the wiring tucked into an existing harness or new loom, with the 'dangling' connections insulated. If you plan things out ahead of time, you can use connectors that will allow you to easily hook up the original ignition in a bind.

-S/6