Just curious what the odds are that my 73 Roadrunner has a seat belt interlock system? It has an indicator lamp on the dash near the console which I believe says "Fasten Seat Belts" but I haven't seen that on any of my other 73's. Just sitting here thinking about my intermittent no cranking issue that occurs at the most inconvenient times and results in a temper tantrum similar to the National Lampoons Christmas Vacation house lighting debacle until it randomly starts cranking again. After checking all the basic things and thinking about it, I'm about certain it has at least part of the interlock system on it but didn't think it was installed until 1974 . Can anyone confirm if 73's got the interlock system. I'm away from the car right now, otherwise I'd go look and have more details for you guys. Just thinking about it now that I stepped away from it for a bit and figured I'd pick your brains. Thanks Guys!

I thought that did not start until 1974 and I thought that was the only year that had it ? They had a small metal box under the hood with a button on it you could press to bypass it I believe ? Ron

I believe the interlock was used in 74. I think 73 just had the seat belt warning buzzer.

Seat belt interlock systems have this bypass button mounted on the firewall near the ECU.



Speaking of the ECU, does it have a GOOD ground? I've had issues with the self tapping bolts coming loose. On my wagon, I ran one of those narrow braided ground straps from the ECU to the block itself. Where the strap attached to the ECU, I used a nut and bolt rather than the self tapping bolt.

(not this exact one, just shown as an example)

Seatbelt light began on 71 being time delay relay controled.

Then 72 and 73 began to be controled by seats and seatbelt retractor sensors, just as a warning buzz and light system

74 began to be interlocked, also with sensors ( this time seatbelt sensors on female buckles ), but just on USA models. Canadian for example even still working and wired the same as USA models, still allowed to crank the engine using a diff control box unit.

I have a copy of the seatbelt interlock manual for '72. If you (or anyone else) want to PM me your email address, I'll put it in a shared Google Photos album so you can access it.

As stated I`m pretty sure 73 never had a interlock to keep the car from starting. You had to fasten the seat belt to stop the buzzer and to turn the light off.