I agree, that is exactly what happened on my 86 300sdl. The circuit board actually burned right there. I ended up soldering a small jumper wire in the relay to take the place of the circuit that had a burned spot. Learned this trick from my GE service engineer when he works on the circuit boards in my MRI scanner. He has done this quite a few times to get us running again while we wait for the new board to be shipped in. I soldered this jumper wire in two years ago and it is still working fine.
JOhn
86 300sdl