No start on 74 Challenger

[74340]

So I have a no start situation with my 74 Dodge Challenger.... I have power to inside the car dome light accessories all come on but when I go to turn the key no power goes to the starter... I can successfully start the car when I jump the starter relay which I've already replaced twice with no different result... The other odd thing is when I leave the ignition and the start position and I press the fan power button ( fan blower for the heat) the engine will start to turn over and I get power to the starter....

Once I do have the car started by jumping the starter relay with the screwdriver... In the car is running I can turn the ignition off and it's successfully turns off the car...

Has anyone ever experienced something like this?

I'm thinking a possible bad ignition switch which I've already ordered?

A side note the transmission safety neutral switch is new... Not that that means much these days

 

[1972 AAR Cuda]

Could it be the seat belt interlock wiring? 74 was the first year for that and it might be the issue...

 

[pschlosser]

when I go to turn the key no power goes to the starter...

A side note the transmission safety neutral switch is new... Not that that means much these days

The job of the neutral safety switch and starter relay is doing this very thing, blocking the starter from getting power when conditions are unsafe - example: the gear selection suggests it is not in neutral or park.

Confirming the function of, and the proper grounding of the starter relay would be the first thing on my TODO list to verify, troubleshoot and confirm. Some relays MUST be grounded to the chassis to work correctly.

These cars are 50 years old, and when changing hands through owners they can and will fiddle with, change, and/or break the factory wiring. Changing out the starter relay, or safety switch won't resolve any wiring problems.

Since you can start the car with a screwdriver, and it otherwise runs fine and shuts off with the key, then the other systems appear to work just fine (ignition, fuel delivery, spark, etc.)

It may be time to crack open the service manual, and study the wiring diagram, and begin checking things out. By checking out, I mean hooking up a meter and confirming the wiring. The problem may very well be the seatbelt interlock system, or a loose/incorrect connection on the neutral safety switch.

The 18 gauge dark blue? wire should be, if memory serves, grounded when in "safe condition" that is, transmission in park/neutral (and for 1974 seatbelts buckled.)

If the 18DBL? wire is not grounded, jiggle the gear selector while testing to see of it goes to ground at any time. For that matter, jiggle the seatbelts and engine bay wiring harness that may show a broken or loose connection.

 

[74340]

The job of the neutral safety switch and starter relay is doing this very thing, blocking the starter from getting power when conditions are unsafe - example: the gear selection suggests it is not in neutral or park.

Confirming the function of, and the proper grounding of the starter relay would be the first thing on my TODO list to verify, troubleshoot and confirm. Some relays MUST be grounded to the chassis to work correctly.

These cars are 50 years old, and when changing hands through owners they can and will fiddle with, change, and/or break the factory wiring. Changing out the starter relay, or safety switch won't resolve any wiring problems.

Since you can start the car with a screwdriver, and it otherwise runs fine and shuts off with the key, then the other systems appear to work just fine (ignition, fuel delivery, spark, etc.)

It may be time to crack open the service manual, and study the wiring diagram, and begin checking things out. By checking out, I mean hooking up a meter and confirming the wiring. The problem may very well be the seatbelt interlock system, or a loose/incorrect connection on the neutral safety switch.

The 18 gauge dark blue wire should be, if memory serves, grounded when in "safe condition" that is, transmission in park/neutral (and for 1974 seatbelts buckled.)

If the 18DBL wire is not grounded, jiggle the gear selector while testing to see of it goes to ground at any time. For that matter, jiggle the seatbelts and engine bay wiring harness that may show a broken or loose connection.

Could it be the seat belt interlock wiring? 74 was the first year for that and it might be the issue...

Somebody was telling me they make a bypass for the seat belt interlock.... Is there a way I can bypass the interlock system? Has anyone ever heard of something or someone doing that?

 

[74340]

The job of the neutral safety switch and starter relay is doing this very thing, blocking the starter from getting power when conditions are unsafe - example: the gear selection suggests it is not in neutral or park.

Confirming the function of, and the proper grounding of the starter relay would be the first thing on my TODO list to verify, troubleshoot and confirm. Some relays MUST be grounded to the chassis to work correctly.

These cars are 50 years old, and when changing hands through owners they can and will fiddle with, change, and/or break the factory wiring. Changing out the starter relay, or safety switch won't resolve any wiring problems.

Since you can start the car with a screwdriver, and it otherwise runs fine and shuts off with the key, then the other systems appear to work just fine (ignition, fuel delivery, spark, etc.)

It may be time to crack open the service manual, and study the wiring diagram, and begin checking things out. By checking out, I mean hooking up a meter and confirming the wiring. The problem may very well be the seatbelt interlock system, or a loose/incorrect connection on the neutral safety switch.

The 18 gauge dark blue wire should be, if memory serves, grounded when in "safe condition" that is, transmission in park/neutral (and for 1974 seatbelts buckled.)

If the 18DBL wire is not grounded, jiggle the gear selector while testing to see of it goes to ground at any time. For that matter, jiggle the seatbelts and engine bay wiring harness that may show a broken or loose connection.

All very good points yeah I'll have to get a good wiring diagram which I knew would probably be the situation but I figured if somebody knew something quick and easy for me to try I'd start there with the easy stuff... The seat belt interlock is definitely a possibility I'm going to look more into that... Along with the neutral safety switch and its connections....The other thing I noticed it does is when the problem first occurred the starter stayed engage even well the engine was running... Actually burned up the starter.... So obviously I put a new one on... It still does it once in awhile or at least it gets sticky... I did replace the positive and negative wires on the battery and to the starter with no change... They were all old anyway and I just did it for good measure

 

[1972 AAR Cuda]

Somebody was telling me they make a bypass for the seat belt interlock.... Is there a way I can bypass the interlock system? Has anyone ever heard of something or someone doing that?

I had to go look myself, because I have a 74 Challenger and have had issues similar to yours (none right now).
Here is more info from for B Bodies only;
74 charger identify this part?
This was a schematic they used (created), so I am not taking credit for this myself...

Hopefully this helps.

 

[Challenger RTA]

That's the Anti theft circuit.

 

[Challenger RTA]

No really STD or Auto? Guessing auto.

 

[Challenger RTA]

Std and auto.

 

[Challenger RTA]

 

[Challenger RTA]

I leave the ignition and the start position and I press the fan power button ( fan blower for the heat) the engine will start to turn over and I get power to the starter....

Or do you mean switch not button? Do you have non stock A/C, heat? Just want to be sure it's stock.

What's happening is. When the ing sw is in the start position it's feeding back through the ACC side of the fuse box.
The fan sw or button then energizes the everything?
I can't say that for sure with out seeing everything. That just a brain cell malfunctioning.

 

[Challenger RTA]

If it's the seat belt warning. This should fix it.
It gets power from the yellow wire for the starter relay. Might be able to disconnect the ground to keep it from functioning. Or disconnect everything just run an other wire to the relay as shown. How ever you do it. There just has to be one wire going out to the relay. Use one of the existing.

 

[Challenger RTA]

1972 AAR Cuda​

Sorry for hacking up your diagram. Thanks for posting it.

 

[1972 AAR Cuda]

1972 AAR Cuda​

Sorry for hacking up your diagram. Thanks for posting it.

No problem, but its not my diagram - I borrowed it from B-Bodies only, but jumping the yellow wire was what I understood to be the fix (bypass)... I plan to try that with mine, since I also have a 74... my interlok was disabled before I got the car and I needed to understand the system to make sure past start issues are resolved so this looked like what I needed.

 

[Challenger RTA]

Bulkhead connector 19 is the ign starter relay wire without the seatbelt circuit. This where there are some difference in the wiring from year to year. In general there all pretty much the same. Not a big deal just look what your doing. This engine diagram also shows other accessories and state spec requirements.

 

[74340]

Tons of great information here guys thanks a lot I've been super busy moving lately but I'm going to try to troubleshoot it here in the next couple weeks and I'll let you know what the outcome is