The 3 terminals on the dimmer switch, and I'm kicking myself for not thinking of that.

I'm pretty sure the middle terminal goes to the light switch (as stated above). Doesn't make any difference which of the other 2 terminals is high and which is low.

'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.