Plymouth Will Not Start but will Crank

I had this problem before , it never really was fixed , here is what I know now , I installed a new reluctor , coil pick up , ingnition box , and finally a new ignition switch , cranks over but will not start , it has 12.5 volts to the starter relay but when cranking the voltage drops to 7.2 volts , it does not start , if you leave the ignition key in the start position and jump the starter lug on the starter relay and touch the terminal with the screw the engine starts , do you think it could be a bad starter relay? thanks.

Clean the bulkhead and the dangling connector under the steering column and or the connector on the ign sw and possibly more terminals/connections as needed to elim that excessive voltage drop. the battery is know to be good correct?

Yes battery is good , cranks fine , the connectors look good , the old switch terminals were all clean and no corrosion was found.

Terminal N in the bulkhead connector is where the Dark Blue wire from "run" on the ignition switch feeds power thru to the ballast resistor. This is most likely where the fault lies. When the ignition switch is in the start position, it bypasses the ballast resistor and send 12v to the coil via the brown wire and terminal Q on the bulkhead. This is why it will run in the start position. Clean terminal N, or bypass the bulkhead connector by locating the dark blue wire on both sides of the firewall and tie them together with a separate wire thru a hole in the firewall.

Was this a conversion to electronic ign? If so, did it ever work right?

Yes if is a conversion and yes it worked fine but now it won't start.

I had the same problem with my car. I found the brown 12v crank feed to the coil was just not connected to the positive terminal of the coil. Someone bypassed the keyed ignition with a starter button to get it started b/c the ballast loses 12v when in the crank position, and the coil gets 12v direct from the ignition switch on the brown wire. It would start randomly before the correction was made when you rotated the key from crank to run and the crank still had some momentum. Hope this helps.

with more thought, what is the voltage at the yellow wire "ign" terminal on the starter relay when cranking? You might also jump 12V to that male yellow wire terminal at the exact same time a helper turns the key to crank. If it straightens out that would point to a voltage drop upstream in that yellow wire circuit. If not that would point to the SR recieving enough voltage and the prob is as you alluded to, the SR itself, poor continuity internally from the Batt stud over to the brown wire terminal when the yellow wire is energized.

The yellow wire going to the relay has 12 volts when in crank position , the car starts when you jump battery terminal to the starter wire (the wire that is attached by the screw clamp terminal on the relay , I found a new relay at the local auto parts store but was for a automatic (I was lucky to get that one) I guess the other terminal has to be grounded when it is for a automatic car , I grounded that terminal and now it cranks and starts fine , I guess my old starter relay was bad? thanks for all your help , I hope it is finally fixed , we started it several times and no problems , thanks again for all your help now and in my previous discussion about this matter.

(1) correct (2) I think you're squared away.