'66 Seat Belt Warning light relay operation?

Whiz (or any other electrical guru),

- I would think I could apply some small voltage to the contacts to cause the relay to close, yes? That would allow me to test the relay outside of the car. So this is the same as asking:

- What SHOULD the voltage through the relay contacts be?

My wiring is so messed up. (Or at least out of spec). There's this strange red wire wrapped around the bottom of the steering column. I finally traced it through, and a PO spliced the seat belt warning light wire and connected the A/C to it. My wiring diagrams say that this should be a wire running off the back of the ignition switch. I have to wonder what else is f*cked up in there. It's almost enough to make me buy a whole new harness and rewire everything from scratch.

Blech.

Steve

Here's how I think it works (couldn't find it on schematic I have). The relay is a thermal, normally closed time delay relay. After turning on the ignition switch, power is applied to the accessory circuits including the seat belt warning relay. Power passes through the normally closed contacts of the relay and illuminates the warning light. At the same time power is applied to the relay, a thermal bimetallic element is heated inside the relay. After a predetermined time period, the heater causes the bimetallic to bend and open the contacts in the relay that feed power to the warning light.

Hence power should be on all the relay contacts the minute you turn on the key. Power should disappear on the contact feeding the warning light after the predetermined time period. Use a 12 volt test light or multimeter to test what's going on at the relay contacts. The relay case itself may have to be grounded for it to work.

Since the Seat Belt Warning Light was only available as part of the Deluxe Seat Belt Factory Option, and not as an Accessory, no separate set of Instruction Sheets were available for it.
However, as noted previously, its installation is shown in the Electrical Assembly Manual. I have attached a copy of the appropriate page, as well as two pages from the 1966 Mustang Accessories" Section of the 1966 Ford Wiring Diagram Manual.

The Relay itself is Ford Service Part Number C6AZ-10B924-A. It is usually ink stamped with the Identification Number of C6AB-10B924-A or -C. It is Tung-Sol Relay # 673.

Over the years, I have successfully repaired several of these. As was mentioned earlier, this Relay has a set of bi-metallic strips that are normally closed (touching each other). As power is applied (ignition switch turned on or to start), the heat from the electricity expands the two strips at different rates, resulting in the strips separating from each other, thus opening (turning off the power) the connection. Just like ignition points, or the points found in the self-winding electric clocks, over time, the points can become burned and rough, or become corroded from sitting for some time (even with new ones that have sat on a shelf for years). All you need to do is to carefully bend up the tabs on the underside of the Relay that hold the fiber "board" in the housing, remove it and then sand the set of points with an ignition file, cardboard nail file, or doubled over piece of 180 or so sandpaper, and smooth the points so they contact each other correctly. As with the clocks, I have found this to be the usual problem, and the "fix" I described usually corrects it. If it doesn't, then be prepared to spend about $75 to get a new Relay, assuming you can find one. Even the new one still may need cleaning.

Hope this helps.

Bob