70 Challenger ignition problems

Electronic ign. Car starts fine when cold but after driving a while it cranks but won't start in start position. You have to let the key return to run and catch it just right to start it. I know there's suppose to be a hot lead for start position. Maybe it's wired wrong but starts fine cold ??

I'm not positive but sounds like typical ignition switch or bulkhead connector problems. The car runs so I would look into the switch on the column and the connection at the firewall. It's not an ignition problem. Get a factory service manual. They are invaluable for making sense with this stuff.

You might want to check the ballast resistor connections. Could be loosening up with heat caused by current draw.

I just had this problem with a customers 70 Challenger. Could not pinpoint it because it never did the same thing twice. Drove me nuts. Installed a Petronix II and now it starts right up. Both the customer and I noticed right off the car even ran better. Ive been stranded by mopars ECU before. Good luck.

Had the same thing happen, it was the ECU

I actually just replaced ecu, distributor, coil, resistor and relay. Should have went with petronix

4 pin ECU/2 terminal ballast conversion I am assuming. In your driveway get hot to where it wont (re)start & have a helper crank it & you under the hood see if you have voltage at the blue/yellow wire/terminal on the ECU pentastar connector and at the coil positive primary terminal. Work FAST while everything is hot for a valid test. This'll get us started.

Check for bad connections as mentioned but don’t overlook the need for the ecu to have a good ground too. Guys all the time change out an ecu and don’t clean the mounting area or run dedicated ground to it. I’ve actially put “bad” ecus back on cars for people and they run fine for years when the corrosion builds up again on the new one.

I agree with the previous reply about the ignition switch and bulk head connector. It might also be the connector under the steering column. The ignition switch has 2 different circuits for feeding the coil, one in the run position, and another in the start position. The start position circuit bypasses the ballast resistor (and feeds 12V directly to the coil) during starting. When it won't start, disconnect the battery and use an ohmmeter to measure circuit resistance from the + battery cable to the + coil terminal (with the switch in "start" position). You will probably measure high resistance. Wiggle the connectors and switch until you see a normal low resistance. That will indicate where the problem is. Good luck.

When it won’t start, hot wire it from battery to coil bypassing all the bulkhead and ignition switch connectors. This will give you a big clue. My money Is on either of those components.