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Electronic ignition woes what am I missing???

70RT4SPD

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This will seem to be a bit lengthy but I’ll try not to ramble on…

75 D350 dodge dump truck. 318 2bbl with a getrag 4 speed. Cab was rotten so it’s been changed to an 87 D250 cab and front clip. The truck has sat for many years but when it ran it ran great. The problem is I have no spark until you turn the key to off and it gives it a “poof” fire or momentary spark on key off not released from key start to run. Replaced the balast, no luck. Bypassed the balast with a jumper wire, no luck. Replaced the ECU (well grounded) no luck. Replaced the pickup coil… no luck. Checked the bulkhead for anything fried all looks good. Also replaced the coil, the starter relay and the ignition switch in the column and you guessed it still same problem. I noticed I was only getting about 9.5 to 10 volts to the positive coil when cranking which isn’t enough to fire it. At this point I’m at a loss and I don’t want to keep firing the parts cannon at it. I’m thinking I’m missing something obvious but can’t figure out what. The 87 cab was an automatic that had a 360 4bbl with a dual pickup coil so there is extra wiring that’s not hooked up. I tried an extra electronic ignition harness that I had from a parts lot to attempt to seperate the ignition system from the truck that was powered by a direct 12v battery operated switch to see if it would make a difference and it didn’t. At this point I have all extra testing wiring and switches removed and hooked back up from the 87 truck harness. Any input as far as testing procedure would be helpful as I keep spinning my wheels on this one. Thanks!
 

65 sporty

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What's the voltage at the ballast resistor? Are you using all the ignition system from the 75 318? If I remember correct when the engine is cranking 12V from the starter relay should go to the coil for start up then after the key is released it runs off the ballast resistor. I am assuming you tied the 75 ignition into the 87 wiring harness.
 

7mopar

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Check all related bulkhead connections and engine grounds. Also check the other 3 requirement needed to make the engine run. You know intake, compression and exhaust.
 
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