Sheesh. Climbed under the TT to check wiring and found that I had failed to connect the ground pigtail to anything, so haven't had a good ground for anything for a year. All other wiring looks great, all brake wires look good, are good grommets where wires go thru axle and no wire looks chafed. As I mentioned earlier, the backing plate, drums, springs, magnets, shoes are great and look fairly new. No grease anywhere inside.
Haven't towed it yet with ground fixed. While not glad to hear others have had the same problem, at least I'm not alone.