I can't look up the part number you gave, but I can't find anything called an air bag sensor relay in the wireing diagrams. Usually if you get a drivers side air bag circuit error it is the "clock spring". This is a unit just under steering wheel that carries the signal to the air bag. Usually the horn and cruse control also don't work. I see this problem atleast once a week or more and it is always the Clock Spring. The part is available from Ford for $93.04. It requires a modification but will work. If you will give me the actual error code I'll look it up and see if I can shed some more light on the problem.

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84 500 SEL (307,xxx miles)