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MSD Pro Billet 8546 distributor to factory Mopar Electronic Ignition Module wiring (no MSD box)

KevinLiner

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The instructions for the MSD 8546 distributor explicitly state that it requires the use of one of their ignition boxes. I wanted to use the factory ignition box, wiring harness, factory tach, etc. I did NOT want the bulky extra box mounted in my engine bay, or extra wiring, modified factory harness, etc. Nor did I want to use a tach adapter to trigger the factory tachometer. I have read that even then, the tach may not work correctly. So (after I had already successfully made a harness, connected it and tested it) I decicided to give tech support at Holley/MSD a call to ask if it could be done. The initial response from the nice young man who fielded the call was “No, you must use an MSD module for it to work. “ I told him I didn’t see why as their distributor had essentially the same magnetic pickup as the factory MOPAR dizzy and that it should trigger the ignition circuit, and that I should simply lose the function of the “multi-spark discharge” from the module. He said he would go check with someone to find out. To my surprise, he returned and said that “theoretically” it could be done if correctly connected (the polarity) but no guarantees. So, I let him off the hook and admitted that I had already done so successfully. He said he was glad that I had called and confirmed because he had the question asked before but that no one had ever told them they had wired one in successfully.
Anyway, the important thing to know is that you need to get the polarity correct or the engine may or may not run at all but certainly will not perform satisfactorily. I have attached some pictures of my harness and a wiring diagram to show how this is done. In order to keep the factory wiring harness from the car and the factory MSD connection on the MSD dizzy, you can make a harness to adapt the two together so that you can unplug as needed. You simply need to buy a pigtail (or cut from a donar Mopar dizzy) to mate with the engine harness and buy a MSD connector (or cut from a MSD module) to mate with the MSD distributor. Then splice together with butt connectors and heat-shrink tubing. I added some plastic conduit for added protection to the wiring. I have read in other posts that it could be done but have never read how to do it. So, I hope this is helpful for someone.
My engine runs fine and my tach works correctly. I may decide later to use the MSD BOX for improved performance but for now I will put some miles on it as is.

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Adam

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Nice work. I just did a similar thing on my Magnum swap 89 Ramcharger. I used a Mopar electronic dist, but modified it with a bracket to the bottom of the dist holding a GM Hei module, triggering an E-coil; completely bypassing the 1988 rudimentary engine computer which is not compatible with performance upgrades. The wiring mods were similar to what you described. Did you just run the tach wire to the negative coil terminal? I should probably make a new post about it.
 

KevinLiner

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Apex, NC
Nice work. I just did a similar thing on my Magnum swap 89 Ramcharger. I used a Mopar electronic dist, but modified it with a bracket to the bottom of the dist holding a GM Hei module, triggering an E-coil; completely bypassing the 1988 rudimentary engine computer which is not compatible with performance upgrades. The wiring mods were similar to what you described. Did you just run the tach wire to the negative coil terminal? I should probably make a new post about it.
Thanks. All of the wiring is new reproduction; some from Year One. Custom engine harness by Bill Evans as the distributor harness has to be longer to reach the front-mounted distributor on the big block. Tach harness also from Evans. Only wire not used was the blue (for a 4 barrel) choke wire .
Yes, the tach from the rally dash is connected to negative terminal of coil.
 
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