88 Bronco fullsize with a built 358w (9.5:1 comp) C6 55k original miles

At some point in time the PO attempted to convert the truck to carb. It was a mess. I finished it and ran a Duraspark II with a factory vac adv, dizzy. rebuilt the motor and trans(roughly 400-420 hp range) I decided to go to a full MSD ingintion its a older 6A box, was a ready to run MSD dizzy, now converted to a Pro-Billet, and a Blaster 2 coil. Wired it all up, the 12v switched same as where the DSII was, started up and broke the motor in. ran great. shut it down for the night, it had to be jumped to start tho, come to find out the Battery had a short. next day ran for barely 8 sec and cut out dead, weak spark from coil, and weak and intermittent spark to cylinders. The dizzy's internal ignition module shorted out. coverted it to a pro billet 2 wire. Had my whole ignition system bench tested. everything worked and produced excellent spark, install it on the truck...stil getting a very weak spark from the coil with KOEO, it wont start. just crank. The box is getting power, when cranking the switched power drops to under 10 for a sec comes up to 10.5-11.5 after the intial drop. Checked and rechecked grounds, installed a new engine-to-frame ground and still get the same results. The MSD help forums have been useless, Does there still need to be a full 12v while cranking? It has a brnad new Motorcraft battery 850-1040, Still has the original starter...Could it be drawing to much? Im pretty good with wiring/electrical, but this is getting really frustrating...this is the last thing that is keeping it from going down the road. I kinda need it, my DD needs some maint done and i need a working vehicle. any insight would be great thanks!

 

I would temporarily run a 12 gauge wire from the battery + directly to the msd box and the coil(wherever the setup you are using requires power). Start it and run it like that and see what it does. You could also run a temp ground wire from the box to the battery negative to try an d eliminate grounding problems. If one of these straightens it out, then you at least know what the problem is. Just have the wire cutters ready when you want to end the test so you can stop the engine.

 

Thanks Franklin, Had to take a break from her and gather my thoughts. couple buddies came over and gave me a hand with it. I originally had the Battery Ground on the Alternator bracket. We moved it directly to a clean boss on the block. Still no improvement. So we ran a wire from Battery ground to the actual ignition box body...Problem solved! The box is mounted on MSD vibration mounts and its bolted to where the Factory airbox was, behind the coolant/washer tank. Now I just need to clean up all the wiring, and get the timing set.