74 Dart won't start - ignition switch - maybe starter relay?

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low_kota

low_kota

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I'm hoping you electrical gurus can help diagnose my problem. I just got the motor back in my dart and it ran awesome for about an hour! I started it at least 5 times, but now I turn the key and get nothing.

I've done a ton of reading on the forum and did a few tests.

  • I tried grounding the neutral safety switch with no luck. I get 0 volts at the starter relay, so the NSS checks out.
  • On the starter relay, with the key in the start position I get 12.5V at the top terminal from the battery. 0V on the square terminal going to the starter solenoid. 0V on the terminal from the ignition switch. 0V on the terminal from the NSS.
  • I have 12.5V at the bulkhead connector after the fusible link
  • With the key in the run position I can get the motor to turn over if I jump the solenoid at the relay, but it will not run.

Any advice on what to try next would be much appreciated!
 
This may not be it, but if your car is a 1974, would it have the seat belt/ starter interlock system? I don't have much experience with that system, but I know a lot of people have to bypass it if the system starts acting up.
 
In run position, do you have +12v to the coil?
 
That seatbelt interlock was a one year only nightmare for 1974.

Do a search in here as it’s been covered many times.
 
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H22A4 said:
That seatbelt interlock was a one year only nightmare for 1974.

Do a search in here as it’s been covered many times.
Click to expand...
Not so sir. It was a pox upon my 75 as well. When I bought the car in 81 the first thing I did was bypass it.
 
I have posted that interlock drawing before but can no longer find it.
 
Tanker said:
Not so sir. It was a pox upon my 75 as well. When I bought the car in 81 the first thing I did was bypass it.
Click to expand...

Hmmmm, I’ve got a ‘75 and it doesn’t have the interlock. It’s a mid mid year build (Feb) so perhaps Chrysler ditched it by that point in the year.
 
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low_kota said:
I'm hoping you electrical gurus can help diagnose my problem. I just got the motor back in my dart and it ran awesome for about an hour! I started it at least 5 times, but now I turn the key and get nothing.

I've done a ton of reading on the forum and did a few tests.

  • I tried grounding the neutral safety switch with no luck. I get 0 volts at the starter relay, so the NSS checks out.
  • On the starter relay, with the key in the start position I get 12.5V at the top terminal from the battery. 0V on the square terminal going to the starter solenoid. 0V on the terminal from the ignition switch. 0V on the terminal from the NSS.
  • I have 12.5V at the bulkhead connector after the fusible link
  • With the key in the run position I can get the motor to turn over if I jump the solenoid at the relay, but it will not run.

Any advice on what to try next would be much appreciated!
Click to expand...

If you have a 74 with the reset button box under the hood, there are two yellowish wires. Splice them together.

Otherwise suspect the bulkhead connector, the ignition switch connector, or the switch itself.

So far as coil check voltage at the coil with switch in "run." You should have "about" 6-10V or so.
 
Rear of the interlock box, yellow"ish" wires My 74 Scamp is over on the left fender apron not far from the ignition module

16kx4d2-jpg.jpg


100_0894-jpg.jpg
 
Other than the interlock, Mopar starter relays are easy. The big stud is always hot battery, and one of the relay contacts. The other contact (load) is the "square screw" which goes down to the starter solenoid

The coil is the two push on flag terminals, one is grounded by the NSS and the other gets power in "crank" from the igntiion switch

Might note that Mopar IGN voltage is a "trick."

IGN1 or "ignition run" is ONLY hot in "run." It goes "cold" in "start." Ignition start voltage is supplied by the bypass circuit (usually brown) IGN2. It comes from a separate contact on the ignition switch and goes to the coil side of the ballast resistor. So it supplies full battery during cranking. THE BALLAST works "backwards" during cranking to supply power to the ignition box.
 
67Dart273 said:
Interlock was 74 only. So if a 75 has it, it's an "early" 75
Click to expand...
Well, mine is a 75 and it has it. I bypassed it but didn’t remove anything so all of the components are still in place including the switches under the front seats. The car’s engine is dated Sept 74. Assuming it would’ve soon after been put in a car on the line, what does that say about early or late?
 
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I got a 74 duster, if after doing the by pass on the reset button on the inner fender, if for some reason the interior lights, radio,cigarette lighter, glovebox light, doesn't work , then that means the interlock module under the dash is bad, its between the radio and glovebox on the wiring harness, you can't just cut it out, it's a light beige plastic box,about 3in wide by 5 in long, they made a green one and an orange one for cars shipped to canada and mexico, those 2 color are plug and play bypass because no seat belt laws were mandatory . I finally removed my underdash harness and found a 75 ,and changed the wiring under the dash, another thing to look at is if under your front seat if the seatbelt buzzer wiring is unplugged, you can rewire it, if you put in new upholstery or seats and unplugged it, it will not start. If for some reason you want the orange or green bypass module under the dash, you can find them on ebay from $150 to $200. I went the route and put the wiring harness from a 75 dart that i bought for $75
 
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Seat belt interlock movie and booklet here:
MyMopar - Mopar Forums & Information - Browse MTSC by Model Year - 1974
Page 1 has the explanations and note that it says the circuits are entirely different than the warning buzzer system.
Page 8 explains the overide switch

low_kota said:
I tried grounding the neutral safety switch with no luck. I get 0 volts at the starter relay, so the NSS checks out.
Click to expand...
Not quite, especially with the 74. Not quite as in, yes you eliminated the NSS as the cause. No in that you can't conclude its OK by checking the voltage at the relay.

To check the NSS, remove the connector from the NSS switch. With the selector in P or N, measure continuity (or resistance) between the exposed NSS prong and the transmission casing. IIRC its the middle prong but check on that.
 
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Tanker said:
Well, mine is a 75 and it has it. I bypassed it but didn’t remove anything so all of the components are still in place including the switches under the front seats. The car’s engine is dated Sept 74. Assuming it would’ve soon after been put in a car on the line, what does that say about early or late?
Click to expand...

August each year was the first month of production for the next model year. Yours being built in September means it’s also an early built 75 model year which explains why it had it. Leftover stuff from the previous model year.
 
robert flippo said:
I got a 74 duster, if after doing the by pass on the reset button on the inner fender, if for some reason the interior lights, radio,cigarette lighter, glovebox light, doesn't work , then that means the interlock module under the dash is bad, its between the radio and glovebox on the wiring harness, you can't just cut it out, it's a light beige plastic box,about 3in wide by 5 in long, they made a green one and an orange one for cars shipped to canada and mexico, those 2 color are plug and play bypass because no seat belt laws were mandatory . I finally removed my underdash harness and found a 75 ,and changed the wiring under the dash, another thing to look at is if under your front seat if the seatbelt buzzer wiring is unplugged, you can rewire it, if you put in new upholstery or seats and unplugged it, it will not start. If for some reason you want the orange or green bypass module under the dash, you can find them on ebay from $150 to $200. I went the route and put the wiring harness from a 75 dart that i bought for $75
Click to expand...

Somebody hacked up the wiring and cut a splice to something else, or something in the harness burned or failed. because the module itself "does not do all that."
 
1969383S said:
In run position, do you have +12v to the coil?
Click to expand...
This is what you need to investigate first. If you have the key in the ON position, and while bypassing the starter relay to crank the engine, you get no spark, you need to find out of you're getting power to the ballast and ignition coil. Sounds like you may have created a bad connection somewhere in your engine installing procedure.
 
^^But you can screw yourself, here, and I've posted this before^^

If you troubleshoot a no-start condition, and DO NOT USE THE KEY to operate the starter, you CHANGE the voltage condition at the coil

1....Normal operation,

A: Key in run, engine stopped. You will NOT see 12V at the coil, you will see much lower, because of the ballast, perhaps 6-10V

B: With key twisted to start and monitoring coil V, it should be "same as battery" while cranking, and it will be whatever the battery is at that point, say, 11V. So crank it, read the coil, move meter to battery, crank again and read battery. You need AT LEAST 10-10.5V while cranking. If not STOP and fix the problem, might be as simple as dead battery

2....Abnormal

A: Again, key in run engine stopped, coil voltage same as (1) above, about 6-10V

B: Cranking engine while jumpering starter relay, YOU NOW are operating with the key in "run" and the battery pulled down further due to cranking load, so the coil will now ONLY GET maybe 4-6V while doing so. This FURTHER reduces spark output if you had any to start with.

ALSO BEAR IN MIND that during cranking, and because of the loss of IGN1 "run" and the transfer to IGN2, that THE FACTORY ELECTRONIC MODULE gets MUCH less voltage because it is fed BACKWARDS through the ballast resistor.
 
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Thanks for all the replies!

I tried grounding the the terminal for the NSS on the starter relay, and nothing.

I have 0V at the coil in start and run

I also had a spare ballast resistor and swapped that out with no luck.

The car doesn't have seatbelts in it, and has started several times without them, so I think the seatbelt interlock has already been bypassed.

I'm not sure if this would matter, but after the engine install it would start and run fine. The only thing I changed before it started acting up was install the alternator.
 
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