The seat belt warning light - on a 1969 XR7 and probably other years/models as well - illuminates a light in the instrument cluster for a short period of time after the car is started. It serves as a reminder to buckle up, but is not connected to the seat belts. It merely lights up for 10 seconds or so when the car is started.
The system operates through what I believe is called a “timed relay” - part number C7AB-10B924-B1. I’ve tried several relays from my “big box-o-wires” and none of them work. Randy Goodling just sent me a couple to try, but it requires a bit of contortion to install this - so I’m hoping someone can devise a bench test method.
In the schematic below, wire 640A traces back to terminal 10 on the instrument panel connector, which is the power feed for the panel that ultimately gets its juice from the “C” terminal on the ignition switch, which is 12v power feed in the “run” position. Wire 520 goes to terminal 8 on the instrument panel printed circuit, which goes to the “seat belt” lamp.
Am I reading the schematic right? Should there be continuity in the unpowered state, and then power heats up the bimetallic strip opening the circuit and turning off the light? That would mean that the thing is generating heat whenever the key is on, which doesn’t seem like a hot idea (sorry, couldn’t resist the pun).
Anyway… if someone knows how to bench test this, please advise.
Here is a picture of the relay and its innards. As you can see, the schematic, although functionally correct, has the connectors oriented opposite of the item. Wire 640A is, in fact, connected to the spade with the little wire wrapping around the bimetallic strip, but that terminal runs perpendicular to the length of the relay, not in line as shown in the schematic.
After looking at this thing some more, I think wire 520 must be a ground circuit, and the lamp in the instrument panel gets power from another source in the panel itself. So, in the unpowered state, continuity is between the spade for wire 520 and ground (the relay has a ground from its case to the end of the bimetallic strip on the far right of my photo).
You are correct, the 520 is a ground circuit. In my 67, the 520 is the ground circuit and the other electrical connector has 2 wires circuits 450 and 365A. 365A provides the power to the Seat Belt indicator lamp. To test your relay, place a 12V fused power source to a light (to the center electrode) . Ground the relay and place a test wire in 520 and place the other end of the wire on the brass body of the light. The light should light (no pun intended). Next. place another 12V fused power source onto 640A. The light should go out as the metallic strip heats up and breaks the continuity to the ground.
All you have observed is correct Rob and yes the thing generates heat the entire time it is on in order to keep the contacts open. And yes, the bulb gets power from the cluster and the relay is the ground for it when the contacts are closed. Bench testing should be a piece of cake.
Good timing on this subject (or bad timing on my part)! My seat belt warning light started lighting intermittantly the other day while I was driving around. Now, it may have been doing this in the past and I never noticed since it was dark when I did notice.
Where exactly is this relay located? …besides “under the dash” >.>
Drivers / Pass side? inboard / outboard? Hooked behind a fuscia colored widget - except on XR7’s, which have magenta widgets?
On my '69, it is located (wait for it) under the dash… above the fuse box/e-brake, attached to the underside of the metal dash. I’ve read that at some point in time this relay (and low fuel relay and the circuit breaker) were moved to the other side of the steering column, behind the radio area.
Thanks all. I put together my test circuit and confirmed that I now have a working relay (thanks Randy). Next time I’m doing yoga under the dash, it gets installed.
