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So I got my MSD box mounted.Being the battery is in the back I plan on running the power to the starter. Where would be a good ground to tap somewhere close?
Seems You have a 1980 C3. If so, it should have a 4-pin, coil-in-cap HEI dist. The following applies if you have that dist.
Seems You also have MSD ULTRA 6AL P/N 6423 CD Ignition Box.
here is MSD link to MSD instructions for MSD ULTRA 6AL (pretty sure that's a "digital" box, Not "analog"). https://documents.holley.com/6639ebb...a3805561c9.pdf
An ICM is essentially an amplifier; and likewise, a CD box is also an amplifier.
Suggest: Do Not Remove the OE 4-pin ICM (Ignition Control Module) inside OE HEI distributor.
Instead, Solely disconnect the ICM, but wire "around" it; in order to connect MSD box. Why? because MSD CD boxes can and do fail; especially digital versions. An Inconvenient Truth: When any CD box fails, it's unlikely there's anyone nearby who can affect genuine repairs.
BUT, If the ICM is in place, and you have wired system so that it can be readily reconnected, you can simply reconnect ICM; effectively bypassing a failing CD box.
I went directly to battery but I have seen people go right to the back of the alternator
My plan is to come off the starter and for the negative the ground wire below the starter both to a junction box that I plan to run my trickle charger with the plug in behind the wiper blades.
Seems You have a 1980 C3. If so, it should have a 4-pin, coil-in-cap HEI dist. The following applies if you have that dist.
Seems You also have MSD ULTRA 6AL P/N 6423 CD Ignition Box.
here is MSD link to MSD instructions for MSD ULTRA 6AL (pretty sure that's a "digital" box, Not "analog"). https://documents.holley.com/6639ebb...a3805561c9.pdf
An ICM is essentially an amplifier; and likewise, a CD box is also an amplifier.
Suggest: Do Not Remove the OE 4-pin ICM (Ignition Control Module) inside OE HEI distributor.
Instead, Solely disconnect the ICM, but wire "around" it; in order to connect MSD box. Why? because MSD CD boxes can and do fail; especially digital versions. An Inconvenient Truth: When any CD box fails, it's unlikely there's anyone nearby who can affect genuine repairs.
BUT, If the ICM is in place, and you have wired system so that it can be readily reconnected, you can simply reconnect ICM; effectively bypassing a failing CD box.
I have the instructions. Looks straight forward. How do I ''wire around it" ?
It seems CD box is resently mounted on firewall.
Is it also presently connected to your HEI distributor? And operating ?
No. I just found the perfect spot to mount it. Not wired yet . I have the instructions for wiring it. It's straight forward and I have done it on 2 C4's before. The c4's keep the ICM in the distributor. But looking at the instructions I'm not sure how I would wire around it.
MSD works fantastic. But the tach doesn't t work. I connected the grey wire as written but nothing . Do I remove the capacitor in line? There goes another $114.00 for a Tach box. I'm confused , the factory Tach is a square wave signal and the MSD puts out a square wave signal.
Last edited by TommyFox; Sep 29, 2025 at 08:57 PM.
MSD box, tips for wiring?
