What's this thing?

[74monacoHT]

I have the service manual cd but can't figure out what this is. I'm in the "learning every inch of the vehicle" stage of new project. The 74 monaco has lots.

 

[DCMC]

What model? What year?

 

[Big_John]

Seat Belt interlock bypass switch

 

[74monacoHT]

Seat Belt interlock bypass switch

View attachment 549019

Thank you! So I just did a quick search. It appears this could interfere with the starter working, if it malfunctioned?

 

[Big_John]

Thank you! So I just did a quick search. It appears this could interfere with the starter working, if it malfunctioned?

It probably could, although most cars I ever saw with the seat belt interlock have had that system disconnected back when the cars were new.

I don't have a good '74 FSM wiring diagram, so I can't look over how it's wired.

 

[Knebel]

That almost looks like a crash switch. That would need resetting after a crash to unlock the seatbelts and the starter maybe?.
I have something similar aftermarket that turns off all electricity to the interior, efi and fuel pumps.

 

[Big_John]

Thank you! So I just did a quick search. It appears this could interfere with the starter working, if it malfunctioned?

This may help:



Thinking about this more, I think there was a TSB on having dealers bypassing these in 1975 or 76, but don't quote me.

 

[74monacoHT]

This may help:



Thinking about this more, I think there was a TSB on having dealers bypassing these in 1975 or 76, but don't quote me.

Very entertaining, and an annoying no-start waiting to happen. What a ridiculous waste of time and resources, including multiple boxes and a huge "analyzer" devoted just to this.

I unplugged the interlock button and the car still starts. I have also tried starting the car without belt buckled. Still starts. So it appears it has been disabled as you said.

I'd like to find out what exact modification was made to bypass this thing back in the day, to confirm it was done properly and won't be a failure point some day. That said, whatever was done has lasted 48 years so far . I will attempt to locate "the brain".

 

[Big_John]

Very entertaining, and an annoying no-start waiting to happen. What a ridiculous waste of time and resources, including multiple boxes and a huge "analyzer" devoted just to this.

I unplugged the interlock button and the car still starts. I have also tried starting the car without belt buckled. Still starts. So it appears it has been disabled as you said.

I'd like to find out what exact modification was made to bypass this thing back in the day, to confirm it was done properly and won't be a failure point some day. That said, whatever was done has lasted 48 years so far . I will attempt to locate "the brain".

IIRC, the usual disconnect was the seat weight sensor under the seat. Again, don't quote me on that. It's a very old memory from the 70's.

I do remember that was the first thing my Dad disconnected on his brand new '74 Plymouth Satellite. I had a '73 Barracuda at the time.

 

[thethee]

Could be that your car is retro fitted with the green control box, p/n 3501500. That way its just a warning system and bypassed the interlock part. Box is located deep under the dash near the firewall if I'm not mistaken

 

[Mr C]

Seatbelt interlock was a US thing only. Canadian Mopars did not have it...Just FYI.

 

[Justin Plant]

My 75 Grand Prix had a similar device. The interlock on my 75 Royal has been bypassed.

 

[CBODY67]

'72 had a warning buzzer and light. Disconnect the sensor under the seat and it did not work. The starter interlocks had more complicated electronics, but still ran off of that sensor under the driver's seat. GM even used some sort of module to run that system.

One of those federally-mandated safety/anti-theft things that the citizenry rejected and disabled. A later version we still have is the "foot brake then shift from P or N. then drive" system.

Enjoy!
CBODY67

 

[74monacoHT]

Thank you all for your replies. I can already see this forum will be a great resource as I restore and realize my land yacht dream.