BTW, the SRS system has a replacement date, located in the glove box. Mine is also a 87 300 and the replacement date is 2001. It might be a good time for you to replace, especially if the work is a little involved. Just something for you to consider while you are working in that area, especially if you plan on keeping the car! Sorry I can't help with the switch problem.

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Deezel
87 300TDT
150,000 miles