bypassing interlock system

-
M

mopar_1974

Well-Known Member
Joined
Nov 5, 2006
Messages
544
Reaction score
1
Location
Mankato, MN
hi, i need help on bypassing of removing the interlock system in my 74 slant six duster. it has been acting up lately and i will occasionally have to pop the hood and bypass the starter relay which can get annoying at times. any help would be great! thanks
 
I would not in any means recommend bypassing the transmission neutral saftey switch if that's what you mean. It's a simple job to fix it. It's probably either a bad neutral switch or the shift linkage is out of adjustment or could even be a bad ignition switch. Next time it happens try putting it in neutral with your foot on the brake try starting it. If it starts it's probably the neutral switch or linkage adjustment.

When I bought my 68 Cuda the idiot that owned it before me had the neutral switch bypassed and I didn't know it. I was installing a stereo system in and put the shifter in low to get more room to get at the stereo and forgot and left the shifer in gear and started it up. Just about went through the back wall of the garage before I got it stopped. Good reason to NEVER BYPASS A SAFTEY SWITCH!! What's worse is my wife could have been in front of it when it happened. Thank God she wasn't.
 
no, its not the neutral safty switch, its a device that won't allow the starter to engage until the seat belts are locked. thanks for the advice tho
 
Ok. Sorry bout the confusion. By the way you described it it sounded like the neutral switch. Didn't know they had an interlock on the seatbelts. Never saw one on an older car before. A 73 Duster I owned yrs. ago didn't have it.
 
I think '74 was their first and only year. On my son's '74 Dart Sport, we simply didn't install the portion of the wiring harness running underneath and connecting the seatbelts. Worked just fine without doing anything special. I believe I read how you can jump the yellow(2?) wires together at the interlock switch for a by-pass.

Jerry
 
75s had it too and mopar put out a bulletin in '76 to bypass...
mine was already bypassed when i got it, but still,unplugging the box she will not start
 
If you look under the seat, you will see a 2 wire plug attached to the springs in the bottom of the seat. There is one on both the driver's and passenger's side. Just unplug the connector and leave the sensor on the seat and it will work fine. Had to do this to my 74 Charger before I would drive it off the dealer's lot. Hope this helps.
 
BEST WAY OF DOING THIS IS TO REMOVE THE CONTROL BOX.

then in the engine bay- remove the reset box- take the two yellow wires and join them and tape. don't tape the yellow wire with the tracer-tape it away! cut the other wires and tape them.

as long as the tranny is in park or neutral it will start.

John Mac
 
i like having my neutral safety switch bypassed. i've been battling engine lag and stalling in motion due to a vac leak. we originally bypassed the NSS because of starting issues of another kind, but i am glad for it now cause if she stalls out in motion i can just restart in drive as i am rolling. i would REALLY dislike to have to come to a full stop in the middle of an intersection, turn off car, and turn back on again from park to get her going again....especially considering i have some random starting issue developed now, too. of course, the stall issue still needs resolving, heh!

a month or so back she had a nice little wire fire thanks to an accelerator pedal bolt breaking, i was in the middle of a busy intersection when she stalled out, went to restart with the man up under the hood diddling the carburetor, thank GOODNESS i had the brakes on cause that bolt went out and she was pedal to the metal. so really, you just use some common sense and remember to keep your foot on the brakes if starting in drive. easy.

so, my .02: bypassing NSS good. putting on thinking cap before starting vehicle also good.
 
hmm,my 74 Impala has this feature.I had no clue Chryslers had them also.On my impala I just disconnected the harness that goes to the seatbelt.Not sure if its the same for Chryslers.
 
on my 74 scamp, with no seats in it, it wouldn't crank by the key, I jumped the 2 yellow wires together at the interlock relay, and problem solved.
 
71_DEPUTY said:
BEST WAY OF DOING THIS IS TO REMOVE THE CONTROL BOX.

then in the engine bay- remove the reset box- take the two yellow wires and join them and tape. don't tape the yellow wire with the tracer-tape it away! cut the other wires and tape them.

as long as the tranny is in park or neutral it will start.

John Mac
Click to expand...
Hey John. I'm running into a problem with my 73 Duster. I used the wiring harness from a 74 Dart that uses the blue interlock box under the dash. After starting the car with most devices plugged into the harness, the blue box started to glow red as if there was a short. I turned the engine off, inspected the box for heat damage and found nothing. Now it won't start and I'm associating the no start problem with the box. Did you ever work a solution to eliminating the blue box? I'd like to bypass the box. D
 
bootsnbolts said:
i like having my neutral safety switch bypassed. i've been battling engine lag and stalling in motion due to a vac leak. we originally bypassed the NSS because of starting issues of another kind, but i am glad for it now cause if she stalls out in motion i can just restart in drive as i am rolling. i would REALLY dislike to have to come to a full stop in the middle of an intersection, turn off car, and turn back on again from park to get her going again....especially considering i have some random starting issue developed now, too. of course, the stall issue still needs resolving, heh!

a month or so back she had a nice little wire fire thanks to an accelerator pedal bolt breaking, i was in the middle of a busy intersection when she stalled out, went to restart with the man up under the hood diddling the carburetor, thank GOODNESS i had the brakes on cause that bolt went out and she was pedal to the metal. so really, you just use some common sense and remember to keep your foot on the brakes if starting in drive. easy.

so, my .02: bypassing NSS good. putting on thinking cap before starting vehicle also good.
Click to expand...

just put it in nuetral and it will start?? dont have to bypass
 
Had a 75 Duster with the seatbelt interlock, the seatbelts were buckled and tucked in the seats, the underseat wires were unplugged, usually started fine, but every one in a while(seems like it did it mostly when it was raining)I would have to pop the hood and push the reset button. Finally I just extended the wires and mounted the reset under the dash using one of the steering column mount bolts, then when it would act up I just had to reach under the steering column to push the reset button.
 
I was looking at the wiring diaghrams on the mymopar sight for the 74 and 75 Darts, I don't see any interlock systems on either years! What's up with that?

I was trying to help figure out bypassing it but without a diaghram I have no idea.
 
Here's what I'd do---I actually looked, and found no diagram The following tests are based on two possibilities:

On a car with no interlock, the start path goes battery---ign sw--twist to "start" ---start signal to starter relay----relay ground through park/ neutral safety switch

There are two possibilities:



1 Chrysler could have placed the interlock to interrupt the starter relay GROUND, that is, between the relay and the neutral safety switch

2 Chrysler could have put the interlock between the ign sw and the starter relay



1. Disconnect the battery, disconnect the underseat connections, and disconnect the relay under the hood

2. Now use an ohmeter/ continuity light on the interlock connector terminals one at a time. See if any of them go to one or the other of the push-on terminals on the starter relay. I would bet one of them does. Note the color and see if they are the same at both ends.

Now we must figure if this wire must go to ground or to power

3. Reconnect the battery and the two terminals on the starter relay. Make sure the car is in park, have a helper hold the key in "start."

4. Pull one wire off the start relay. Probe the WIRE you removed for power in "start". If none, leave it off.

Now ground the exposed starter relay terminal and see if the engine cranks. If it does move to step 6

5. If the disconnected wire shows power, connect to the relay, pull off the opposite wire. Ground the terminal you just exposed. The engine should crank. If so, move to setp 6

6. If you get this far, it means the interlock relay is in the "ground" circuit of the starter relay.

Now connect that wire back up to the starter relay, move to the interlock relay,

AND YOU SHOULD FIND that the last wire you just played with is the same color--same wire--that you noted earlier

What all this just "found" is that the starter relay goes to ground through the interlock and on to the neutral start relay on the trans.

7. So now, disconnect the interlock, make sure the starter relay is again hooked up

Probe the wire you previously found at the interlock connector with voltmeter or test light to ground, while twisting the key to "start" you should get a light. Further test this by grounding the wire, and the engine should start NOTE THIS WIRE

If so, all we must do if find the path to the neutral start switch.

First look over the harness, or look over your diagram, and see if the neutral start switch colors "come up" to this connector (interlock relay.) confirm by probing the connector-----

Disconnect the battery, and with your helper able to go from drive--to park--to neutral, see if there's a wire at the interlock connector that grounds as the shifter goes to park/ neutral.

IF this happens, now all you must to is permanently jumper this last wire to the one you found in step 7.

IF NONE OF THIS WORKS it means the interlock relay is interrupting the start signal from the ign switch, instead of being in the ground circuit

So------

1a. Disconnect the interlock relay, have a helper twist/ release the key while you probe the connector for voltage IN THE START position.

If you find it, this is probably then routed to the start relay NOTE THIS WIRE

2a Disconnect the battery disconnect the push on wires from the start relay, use an ohmeter/ continuity checker to probe the interlock connector and find the wire that goes from there to the start relay.

3a Check your work by jumpering this last wire in the connector to the wire found in 1a

The engine should crank, and should not crank in drive. If this is the case, just permanently jumper / splice these two together
 
UPDATE. Just dragged home a '74 Duster which I started to junk out. I cannot power it up, but tried to trace some of it for you I believe you need to jumper (EDIT) The yellow with the yellow/ stripe the yellow goes down to the start relay, and those two are connected to the contacts in the interlock relay

16kx4d2.jpg
 
Great post 67Dart! This is just what I need for my Interlock bypass.
 
Hey BigD, my 74 still has all of that on it. The plugs under the seats have been unplugged ever since I've had it. I got it from original owner at 42,000 miles. Dug into it one time and pulled the reset switch under the hood apart and found the contacts had been soldered together.

The blue box your talking about, is it the one mounted right above the fuse box? If it is, I've wondered what that was for the past 20 years. What exactly is it? All I see inside it is a circuit board.

Also, is there a key or seatbelt buzzer on these cars? I've never been able to find one. I know the earlier ones are mounted beside the glovebox compartment.
 
BarryC said:
Hey BigD, my 74 still has all of that on it. The plugs under the seats have been unplugged ever since I've had it. I got it from original owner at 42,000 miles. Dug into it one time and pulled the reset switch under the hood apart and found the contacts had been soldered together.

The blue box your talking about, is it the one mounted right above the fuse box? If it is, I've wondered what that was for the past 20 years. What exactly is it? All I see inside it is a circuit board.

Also, is there a key or seatbelt buzzer on these cars? I've never been able to find one. I know the earlier ones are mounted beside the glovebox compartment.
Click to expand...
That blue box is the seatbelt interlock. All of the main wires coming from your ignition switch go to this unit but it they are not in series, meaning that if you disconnected them, they are not vital to the operation of other electrical items. If you value the seatbelt buzzer, seatbelt light and engine cut off, then you will need this item. If you don't value them, then the whole unit can be bypassed. This was my main focus in my search to find the gremlin in my '74 wiring harness into my '73 duster. This was quite a dilemma as I spent lots of time resolving it. The soldered connection you mention was a solution to preventing constant resetting of the button under the hood. And yes, it is a circuit board.
 
Bumping this post up for those of us with '74's. My Duster has had some kind of bypass done to it, but not well. Sometimes it starts without the seat belt buckled, sometimes is doesn't. Gonna have to go check it out, this should definitely help!
 
I lost power to my head lights, won't start and the battery is new. 12.7 volts.
If I jump the fuse box, everything works and it starts with no problem, runs well but as soon as I turn it off, nothing again. Any ideas? Starter, starter relay, interlock, fuses and ignition switch are good. Help
 
74 dart swinger said:
I lost power to my head lights, won't start and the battery is new. 12.7 volts.
If I jump the fuse box, everything works and it starts with no problem, runs well but as soon as I turn it off, nothing again. Any ideas? Starter, starter relay, interlock, fuses and ignition switch are good. Help
Click to expand...

Please repost this in a new thread
 
A few post talk about bypassing the blue box under the dash on the interlock system. Could someone go into more detail on how its done?
 
You must log in or register to reply here.
-

Back
Top