1974 164E BW35.
I replaced the ignition switch because the fuel pump wasn't priming. The buzzer then sounded normally and not intermittently as it had been and the accessory lights came on as before and the fuel pump now would prime but I got no crank in position III. Nothing.
I wasted a whole day scratching my head, testing and swapping components and searching for something called a starter cut-out relay.
The next day I found a section in the shop manual that showed the location of the starter cut-out relay and mentioned something nearby called a seat belt interlock. Hmm. What's that?
It described how, if the front seats were occupied and the seat belts weren't fastened the car would not start. Oh? Really?
Go to car, fasten front seat belts, car starts immediately. :[ Only later did I get the back story on this device and the NHSTA. It was the 1970s...it was a different time.
Anyway, I had 'fixed' a number of things that I didn't even know were broken when I replaced the ignition switch and now they are 'working'. The problem now is that the buzzer never goes off even after the car starts. Ugh.
Disconnecting the seat belt interlock after starting the car will stop the buzzer but the car will not start again after it has been turned off unless I reconnect the seat belt interlock. I doubt I can find an occupant sensor device for this car so if anyone knows the best way to disable the seat belt interlock let me know.
Thank you

For a short period of time, I remember that new US cars had to have a buzzer to warn drivers to fasten their seat belts.

Our 1972 VW 411 had this feature. It also had a warning light if there were some weight in the passenger seat.

The hue and cry in this country about the buzzer caused that feature to be dropped, and dealers were allowed to disable this device because many drivers connected their seat belts and sat on them!

I always used seat belts because race cars had them. I installed them in all my cars since 1964 when I got my driver's license!.

I never heard the buzzer in my 411, but when I sold it to my sister when it was 8 years old, I had to disconnect it for her!

I was hoping to find a factory issued dealership direction for disabling the system but I think I can work with what 142 Guy said earlier.
Thanks Planetman, I have a green book for 1974 which I am studying the diagrams...How much are you asking for the 6 pin Neutral Safety Switch?
I also thought about trying to get the system functional again but I wanted to ask you guys if that would be a fool's errand?
Thanks!

I don't have a wiring diagram for the 1974; but, the seat occupancy sensor will likely be a switch in the lower cushion which opens or closes (the more likely case) because of the weight of the driver on the seat. Checking the starter interlock description in the service manual will probably clarify the switch function. Assuming its a contact closes when occupied switch, all you need to do is find the plug from the body harness to the seat harness (has to be a plug to allow for seat removal), disconnect the plug on the body side and jumper that plug to provide a constantly occupied signal for the interlock. If its a contact open when occupied switch all you need to do is unplug the harness.

Of course, you could also just completely by-pass the starter cut out relay with a jumper. Then your 140 would be just like a 1971 140.

I have the 1974 Volvo 140 green book repair manual on my computer and I can send you the electrical section which includes a wiring diagram.
--
Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502
hiperformanceautoservice.com or oldvolvosonly.com

I have the 1974 Volvo 140 green book repair manual on my computer and I can send you the electrical section which includes a wiring diagram.
--
Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502
hiperformanceautoservice.com or oldvolvosonly.com