No crank with key troubleshooting

[74Runneer]

74 Road Runner with a 360 that won't crank over with the key. I can jump the contacts on the starter relay and it will crank. I ran a jumper from batt neg to NSS terminal on starter relay and still no start. This tells me that the NSS is not the issue. I measured voltage at the yellow wire while key in start position and I get 10.8v. If I jump 12 volts to the relay then it cranks. So I know that the relay works and my issue is from low voltage on that yellow wire.

I took the connector at the bulkhead in the engine off and measured voltage from pin 19 (yellow starter relay wire from ignition switch) on the firewall bulkhead while key in start and it reads 12 volts. (Battery is at 12.5 volts, there is a 0.5v drop from the seatbelt interlock control unit). When I reinstall that bulkhead connector and back probe that pin 19, it drops back down to 10.8 v.

Looking as the service manual it looks like there is two ignition start circuits coming from the key switch; one goes to seatbelt interlock and then starter relay, the other goes to coil, ballast resistor ( which I have bypassed with FBO ignition system), alternator, and voltage regulator.

If I disconnect the brown (ignition start to coil) wire on the bulkhead connector from inside the car and then turn the key to start, then I get 12V to the starter relay.

My brain is mush from staring at the schematics for so long, where do I go from here?

 

[70chall440]

Ok, is this something that just happened (meaning did it work before)? If so, then it has to be something simple such as the wiring from the ignition to the relay. I had a 74 RR but do not at all remember anything with the wiring so I cannot be of much specific help there.

Don't over think it, I would wager it is something simple like a connection, fuse or small component.

 

[74Runneer]

No, its been like this for a few years now. I noticed it after I pulled the old 318 and put in a 360 about 2 years ago. I installed a new engine wiring harness at the same time I swapped engines. I have since replaced the alternator with a power master unit and I also pulled the bulkhead connector out and inspected and cleaned every connection.

 

[70chall440]

Check the wires that go from the switch (steering column) to the harness/bulkhead connector. There is a connector that allows the column to connected to the main harness, check that.

 

[74Runneer]

The connector on the steering column is good

 

[Ray70Chrg]

It seems that you are indicating that the seat belt interlock is somehow loading down that circuit. Can you disconnect the wires going to and from the seatbelt interlock and jump them together. My car is a '70 so the wiring does not have seatbelt interlocks. Does the interlock system also include the passenger side?

 

[toolmanmike]

I had issues with a couple of Mopars with the bulkhead connector like @70chall440 mentioned above. You might be able to wiggle the harness going through the connector and get it to crank.

 

[1STMP]

Try holding the shifter up with a little extra
pressure while in park. Things get worn,
neutral safety switches "walk".

 

[1STMP]

Warn should be worn...spell check strikes
again....

 

[toolmanmike]

Warn should be worn...spell check strikes
again....

Fixed

 

[Richard Cranium]

When all else fails............

 

[74Runneer]

I'm gonna try swapping seatbelt control modules but I don't think that's the main issue. There seems to be a voltage drop somewhere downstream of the bulkhead.

 

[74Runneer]

I have confirmed that the neutral safety switch works. I have even jumpered the grounded side of the starter relay to the battery negative and get the same results. The issue is that I'm getting under 11 volts at the starter relay. It's weird because I can unplug the connection at the ballast or unplug the blue field wire on the alternator and the voltage will jump back up to 12 volts at the starter relay.

 

[Ray70Chrg]

I have confirmed that the neutral safety switch works. I have even jumpered the grounded side of the starter relay to the battery negative and get the same results. The issue is that I'm getting under 11 volts at the starter relay. It's weird because I can unplug the connection at the ballast or unplug the blue field wire on the alternator and the voltage will jump back up to 12 volts at the starter relay.

Have you tried to crank the engine w/key when the blue wire is off the alt.

 

[74Runneer]

I havent, but I'm fairly confident that it would crank over.

 

[Ray70Chrg]

That would tell me that the alt. is suspect. Try it w/key.

 

[74Runneer]

But I just replaced the alternator with a new powermaster alternator and it acted the same with both the old alternator and the new. I know you can get bad parts out of the box but I don't think it's the alternator itself. I think it may be the wiring in that charging circuit.

 

[74Runneer]

I'm out of town but I'll try it when I get back.

 

[Ray70Chrg]

Forgot about the part where you replaced the alt. On my 70 charger, the blue field wire on the alt. goes to a splice that feeds one side of the ballast resistor but also goes to the voltage regulator and to the bulkhead connector. The other wire from the voltage regulator (green ) goes back to the other field term. on the alt. Your wires may be different colors on your '74 but I think this brings the voltage regulator into question.

 

[NoCar2023]

Voltage drop in the ignition switch is common; you can replace the switch or install a hard start relay kit.