So I've fully populated the truck's lightbar with strobes, but I can only get two power supplies to work at a time. Before I put the 3rd P.S. in ("Strobe C" on flasher board), I had the original (4 corner strobes; "Strobe A"), and a 2nd one I put in (2 front and 2 rear inboard strobes; "Strobe B"), and 2 rear-facing, halogen flasher lights. With the slider switch in Position 1, the 4 corner strobes came on; Position 2, 4 corner strobes, plus 4 inboard strobes (2 front, 2 rear); Position 3, 4 corner strobes, 4 inboard strobes, and 2 rear halogen flashers.
Now that I've added a 3rd strobe power supply, I only have 2 power supplies working at a time. I know the 3rd P.S. works, because it powers on its strobes when I move it from Strobe C to Strobe B or A, and when I move the original power supply for the corner strobes to Strobe C, they won't come on. I've checked all the fuses on the flasher board, and I found an apparently unused 2-pin plug with one wire in it, and plugged it into the 2-pin slot under Strobe B, but get the same results.