How very convenient that I drove my 87 to work tonight. It's fuse 13, a 16A (red) fuse. Shared with turn signals. I found that out on my old 87 which had a broken center console- the switches were adrift and shorted out, causing loss of turn signals. If the signals work normally the problem is elsewhere.
First thing to check for- the plugs under the seat. 2-pin, red and black wires. They get unhooked by people catchign with their feet. Obviously easy fix. The bulbs do burn out in these switches and the plugs to the back of them can get pulled out by stuff getting jammed down into the center.
If they still seem to not work, remember they do have a thermostat and won't work on a hot day, and also you can take a resistance reading at the connector, using a multi-meter. You can pick up a useful meter for $20 or less. This meter will also let you check for the presence of 12VDC at the car side of the seat heater plug. WIth this info you can follow the problem to its source. I'd be surprised if the passenger seat heaters are failed, but it's common for the driver's side to get broken.
Good luck!
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Rob Bareiss, New London CT ::: '87 244DL/M47- 221K, 88 744GLE- 202K, 91 244 181K, 88 244GL 145K