MSD install question

[81xsproject]

I am have a question about wiring in my pick-up coils. Which wires should be the pos and neg on the PU wires? Here is the MSD diagram.

[DiverRay]

Looking at the diagram, I think it wants the HT Coil wires, NOT the pickup coils. I do NOT have my book handy, but I think it should be the light green and orange wire on the XS harness to grey, with the other two wires to white and green. On the early machines, we have the ballast resistor, so that will help pinpoint the wires.

[audijunky]

Looking at the diagram....gives me a headache. from the looks of it there will be four coils?? if the outer ones are new ones from MSD, then why would you need to connect wires to and from the old coils?? It must be the pick up coils that the center of the diagram is talking about and not the old ignition coils. IDK I dont have an MSD igi.
Good Luck

[81xsproject]

No there is a special igi for that and this is not it.

[81xsproject]

It looks to me like it sets up just like the stock iggy. Wires go from iggy to PU coils and from iggy to coils.

[TopCatGr58]

Hey Jessie,

After reviewing that wiring diagram, I would say that the two yellow wires going to the PU coils are the (+)pos, and should connect to the two gray on the MSD system!

I've got the diagnostic info that Randy sent me after he had to shut down his web page, haven't made the time to get it converted into a tech tip and reposted, but I think there's a PINOUT diagram in it, just can't remember if it's labelled with the needed + or - designations??
T.C.

[ccogswel]

I don't mean to add to anyone's confusion. But It looks to me is if you have all this MSD set up I assume you have their coils too. If that's the case I think all you need to do is take the orange and gray wire and connect them to your gray wires on your MSD box and take your red/white wire and connect it to the white and green wires of the MSD box. Or maybe backwards of that as I see the MSD has two gray wires and a white and green. And on the wiring diagram you have the red/white wire supplying two and the orange wire and the gray one going to separate place's on the coil. That's why I say maybe backwards.

I don't think I was any help but I hope someone could understand what I was trying to say. I can do stuff like this in my mind but it's have to type it out right.

Any way Good Luck!

[DiverRay]

Jessie,
ccogswel has the answer!! the red/white wires are the coil + lines, and the Orange and the second wire are the coil -. the color difference will be 14 and 23, but I don't know what one powers what set.
The MSD box is designed to hook up in place of the STOCK COILS, so THAT is the wires you need to connect it to.

[randy]

The way I read it, the MSD needs your stock TCI and pickups to generate the signal for the MSD, remove your old coils and feed the old coil wires into the MSD box.

The original coil positive is Red/White and the coil negatives are Gray for 1-4 and Orange for 2-3.

Oh, remove the ballast resistor and plug the remaining harness leads together.

[81xsproject]

I don't think so. In the rest of the MSD installation manual, the PU coils are referred to as "coils". Which is what I think is causing confusion. I maybe wrong. I sure hope that is the case or I wasted a bunch of money on my '78 advance assembly.

[81xsproject]

So if I do need to use a TCI, can I just swap and use a 2h7 unit with my mech advance?

[randy]

YES!

[81xsproject]

What about this set-up. Could I do this with the stock PU coils, or would 12v be too much juice? This is for an aftermarket signal amplifier.

[randy]

That should work, but you might want to check the specs on the trigger coils required for the MSD unit. Ours are inductive and between 600-800 Ohms.

[TopCatGr58]

Hey Jessie,

Okay, after seeing your second diagram, I now see that in the 1st diagram that they were wanting the wires that went to the old high tension plug coils, the power wires that feed the old coils and the trigger wires that the TCI controls to cut power to the plug coils to collapse the coil fields to generate the big spark plug voltage. This way, when the TCI would have been triggering the OLD plug coils, it would THEN be triggering the MSD unit which in turn would trigger the NEW MSD coils, but would use the OEM PU coils and the OEM TCI. SO I was in error about the use of the yellow wires that are part of the 4 wire plug from the PU coils to the TCI ....in this setup.

The 2nd diagram shows the MSD unit using the PU coils to trigger the MSD to send power to the plug coils, not using the OEM TCI, because the MSD would act as the TCI. I thought I remembered seeing timing curve chips in your other photos in the other thread that can be used with the MSD?? I thought your plan was to use the MSD to replace the TCI?

Those yellow wires are the power wires to the PU coils, you should be able to turn on the power and test them to see IF the TCI is putting out 12 volts to them, that way you can then know if you can just bypass the TCI and connect the MSD directly to the PU coils at that PLUG!

With the 81 and the MSD, you'll have the vacuum advance, but not the cent. adv. curve....unless it's programmable with the MSD unit which I thought it was from seeing all of those different advance curve chips!?

IF you use the OEM TCI, then it seems about all you're doing is adding a fancy ignition coil/spark system, but you still have the old OEM TCI....which can eventually die....and I thought you were wanting the MSD to be able to replace the TCI???
T.C.