Read the manual. Generally the Stern switch matrix chart has a note next to switches that don’t have diodes. And sometimes the diodes are off the coil on tags under the PF. Follow the wires.

If you have a bunch of switches (on the same row or column) not working, it’s generally because a wire is off “upstream” on that row.

Get the matrix, find the affected row/column, and test it from start to finish. Eventually you’ll find the issue. The first switch will work, the second one works, the third one doesn’t. So the problem is between 2-3. Wire off, wire cut, wire broken in the middle (hard to spot)

You can test the connections with a meter on continuity. Hold the wire on the start of the row (first switch) and buzz every switch down the row. Every link in the chain should buzz when you hold your meter on it. You should have a long chain from the end switch all the way back to the molex on the CPU board.

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