'72 seat belt warning relay

[Tom L.]

Upon departure to carlisle I found that the seatbelt warning light would not turn off. My car is an early '72 build (Oct. '71) and according to the JM there is a 15sec. timer that turns off the light. Prior to it's failure it worked as described in the JM. I searched the archives and found some discussion about this timer and it is apparrently a SYLVANIA 03961500 part. The post is a few years old and I found that there was little else about it's replacement.

My questions are where is it located (the AIM doesn't say, the only page I see in it about any seatbelt relay is a revision made after my car was built)? Does anyone make a replacement? If not, can it be repaired?

Thanks!!

[Jack H.]

Re: '72 seat belt warning relay

I'll venture a guess that the component is integral to the center console's seat belt warning electronics.

The earlier cars had a 'PUSH' button below the warning lamp that required the driver to actuate to extinguish the lamp. The printed circuit board that forms the center cluster's warning zone had a relay built into it. When you pushed the button, that latched the relay to turn the warning lamp off and it'd stay off until the circuit was powered down.

A self-latching relay with integral delay is a child's play design evolution. Instead of having a manual button/switch to latch the relay, you design in an RC time constant based trigger using discrete resistor & capacitor to set the delay profile. When the capacitor charges to its 'threshold' level, the relay self-latches.

It might be there's nothing wrong with your car's relay and either the resistor has opened up or the capacitor has gone bad (internal dielectric break down) and one or both need to be replaced. But, in either case, my HUNCH is you're looking a pulling the center cluster to troubleshoot and repair...

[Don L.]

Re: '72 seat belt warning relay

Lynn/Jack - The relay that is in question here can be found behind the RH dash pad. It actually screw-mounts to the sheet metal under the windshield , inboard of the radio speaker and has a 3 prong plug "L" shaped electrical connector, tying it to the dash bulb. The timer/relay itself is a cylindrical aluminum part, similar in appearance to a flourescent light starter. It's about 1/2" in diameter and approx 1" long.

I too have an early '72 MY car with the 15 second timer and mine was not functioning when I bought the car. I had trouble finding a replacement, so I had a radio shop repairman make a tiny circuit board and replaced the internal wire/contact setup with the board. Unfortunately, this board failed after approx 1.5 seasons. I'm told this happened because the board was made without a needed heat sync. Anyway, as I fretted over my loss, I remembered how GOOGLE is my friend. I happened to GOOGLE the GM part number (I think it was 3961500) and whad'ya know - there was one on ebay. I bought it now and live happily ever after. My symptoms were a little different than those that Lynn describes. Originally, the broken fine wire wrap caused the light not to glow at all. The second failure (after rebuild) caused the light to glow only very little, not noticeable unless in the dark.

If it's the switch you need, a saved search on ebay might be a good idea. Alternatively, you may want to consider the re-build option, just be sure to check out the possible need for heat sync.

Hope this helps.

[Tom L.]

Re: '72 seat belt warning relay

Don, thanks for chiming in, I knew someone would. I'll have to remove it and have a look. Being as the light is staying on continuously I'm thinking that the switch contacts are stuck closed. Do you recall if the can that encloses the device can be removed? I'm hoping to open it to see if that's the case. If it is the contacts may only need to be free'd and cleaned up. I'll let you all know. Thanks!!

[Don L.]

Re: '72 seat belt warning relay

The switch can definitely be opened. The cap is thin aluminum with 4 tiny tabs. The tabs fold over the base and thereby secure the cap to the base. CAREFULLY straigten the tabs and slide the cap off. Do your magic inside and close her back up.

I hope this works. I can't imagine that the constant contact is good for the life of the switch so I'd prioritize this work if it was me. If a delay is needed, you might consider reaching up under the dash and unplugging the switch from the harness until you can get to it.

Good luck. Please let me know how it goes...

[Tom L.]

Re: '72 seat belt warning relay

I got a chance to remove and inspect the timer today. It seems to operate fairly simply. There is a heater inside that is energized when the key in at all times (not sure if I like that), it heats a bi-metal strip that once heated bends enough to hold the contacts open. Once the key is turned off power is disconnected from the heater, the bi-metal strip cools and the contacts close until the key is turned on again.

Unfortunately the contacts are fine and the heater is open, no continuity, so no heat is generated to act on the bi-metal strip. Right now my only option is to unwrap the heater, which is simply a wire of an unknown resistance and covered with cloth insulation, and try to find the open part of it and repair it.

Below are a few photo's of the relay, 2 of it in one piece and one dissasembled. In the last photo you can see the heater wire wrapped aroung one side of the contacts.

Unless... someone is aware of a source OR can identify the type and length of heater used so it can be replaced. Now it seems to be a long shot either way, ALL help is appreciated. thanks!!!