[Jack Hagerty]

I need some help from those of you mature enough to remember the great social engineering experiment in 1974 called the "Seatbelt Interlock." Here's a little background for you young'uns:

This was a bit of nanny-state legislation that made it impossible to start a car unless all of the seatbelts were fastened on the seats that had people in them. This meant sensors in the seat cushions, sensors on the belt reels and a logic box to make sure all the conditions were met before allowing current from the starter switch to flow to the starter relay.

As you can imagine, there was quite an uproar from people over this heavy-handed intrusion, especially since it was not selectable and you had to buckle up just to pull your car into the garage from the driveway or belt in the bag of groceries on the passengers' seat. The law was repealed with lightning speed (at least by Washington standards) and by the end of the year it was legal to disconnect the interlock.

OK, here's my problem:

My car is a '74, but I didn't buy it until August '75 (still new). It has the interlock, but the logic box had been bypassed by the dealer so I never experienced the joys of dealing with it. I haven't really thought about it for decades until a few months ago when the ignition switch wouldn't engage the starter. It powers up fine, but when I twist over to "start" all I get is a buzzer that I took to be the key buzzer. I figured that the switch was wearing out (things do that after almost 36 years and 516,000 miles of daily driving!) so I got a replacement from APE and installed it. Same exact symptom. It then dawned on me that the buzzer I heard in the "start" position isn't the key-in-lock buzzer, but rather the buckle-up-you-idiot buzzer (the sound is very close but noticeably different once you listen for it).

I spent a couple hours with the wiring diagram tracing out how the logic box was hooked up and how it was bypassed. The big surprise was when I took it out of the car (it lives up in the passenger's footwell right next to the glovebox) it appeared to be completely intact. The big 15-pin connector was still attached and it was still, as near as I can tell, wired into the system as per the diagram. OTOH, there were some old water stains from about 15 years ago when I had a windshield gasket problem, and when I opened the can, the circuit board inside was badly corroded in one area.

My two questions are:

1) How was this unit "bypassed" by the dealership if everything was still correctly connected? The car starts fine (well used to) even with no belts connected.

and

2) Can I really bypass this thing by jumpering the pin coming in from the ignition switch directly to the pin going out to the starter relay?

Sorry this was so long. Thanks for sticking with me this far!

- Jack

 

[Jack Hagerty]

My guess as to bypassing it is that they just jumpered the wires at each buckle attachment point. Check under the seats, maybe?

I think you may have put your finger on it. The sensor connectors under the seats and the ones on the belts have always been disconnected. Maybe it was that simple? Just disconnect all the sensors and the box thinks there's no one driving the car. That means that for almost 36 years I've still been going through this logic box that for the past 15 has been corroding away. There are two big relays on the circuit board that I presume is what did the switching to the starter.

The box was made by Bosch and is very crudely assembled, obviously dashed together in a hurry. It's a thin steel box just staked over the connector at four places without any kind of seal, hence the corrosion. Definitely not up to their usual standards.

- Jack

PS - I agree about he '70s!

 

[Jack Hagerty]

The factory method of bypassing the seatbelt interlock device is to cut wire #13 (black/green) at the device and electrically connect it to wire #10 (black/red). This will allow the starter relay to be triggered directly from the ignition switch whether seatbelts are on or not while still retaining the seatbelt buzzer and warning light if the belt is not buckled.

Thanks. From my reading of the diagram, this was what I intended to do, but I had to check with someone first. I didn't want to let the smoke out of anything that couldn't be replaced!

I just checked the car and all the wires are intact. It looks like the dealer just unplugged the seat sensor connectors.

- Jack

 

[Jack Hagerty]

I had issues like this as well and it was the relay on the firewall that had failed. Everything else seemed fine but the starter would not turn.

My car was built before the firewall relay and had the "won't stop cranking" problem. I added a relay and it's been fine ever since.

- Jack

 

[Jack Hagerty]

Jack,

If for some reason your bypass still requires a functioning module, I'm sure I have one from a '74 parts car. Untested. Cost of shipping.

Thanks. If the bypass doesn't work, I'll contact you.

- Jack

 

[Jack Hagerty]

Wow! buzzers that work, that is truly amazing necessitating a tip of my hat to you!

Actually, AFAIK, this one had never actually been used, which is why it took me so long to recognize it for what it was.

BTW, the car starts fine now. I noticed that the connector was based on Molex pins, so I just made a jumper with two males and plugged it into #10 and #13. Works like a champ. I just can't believe I've been going through that box all these years!

- Jack

 

[Jack Hagerty]

Hi Jack, I've had my '74 since '86 and never had this problem. Somebody before me must have 'fixed' it. I put Simpson belts in the week I got it so, no worries. But, I did find the device somewhat recently...

Yes, that's the culprit. I've taken some photos of what's inside, but I can't seem to post them. This site seems to want a URL rather than an upload. Is that right?

I replaced my belts also about five years ago, but I used a set out of a Milano. I used those for the rigid stalk on the inboard side and the more robust lockup mechanism. Surprisingly, they bolt right in except that the belt has to be shortened about two feet for the reel to take it all up.

- Jack

 

[Jack Hagerty]

To bypass the Bosch interlock device, does one simply need to jump the wires at 10 and 13 (red/black and green/black)? Do you accomplish that by jumping those wires and then leaving the multi-pin connector un-plugged from the interlock box? I've tried this and get no cranking.

It sounds like you might have another problem somewhere. Your description of how to bypass the box is exactly correct. I just made up a short jumper using some male Molex pins (it's a Molex connector) and plugged them into 10 and 13. You have no choice but to leave the connector unplugged.

I've been messing with and pondering this for the past few weeks, since my alternator light's flickering coincided with noises under the dash. I found the original buzzers - mentioned in an earlier post to this thread - were being actuated, in exact synch with the flashing of my alternator light. So I removed the buzzers. Now the interlock box itself is doing the same synchronized soundtrack with the flickering alternator light; I'm assuming the interlock box has a relay(s) inside which is where the buzzing is coming from.

This usually indicates an intermittent short or open. Yes, there are two relays in the box (I have photos, but I can't seem to post them here) but they are for switching, not buzzing. The "buckle up" buzzer I mentioned sits right next to the "key-in-lock" buzzer just under the instrument pod (which I presume is the one you removed). If your interlock box is buzzing, obviously still plugged in, then maybe one of the sensors in the seats or belt reels is at fault. These should all be unplugged.

If you want to mail me directly at [email protected] I can send you the pictures.

- Jack