More tests...
Mike,
My tests were run with a 12" long Y with 20 gauge wire and a 24" long Y of standard gauge. No extra length beyond the Y's.
I have 4 5645s and 2 5625s. I tried all combinations of 5645s and 5625s in dual and single servos. All the singles worked and all the duals did not work.
I tried your suggestion of using two Ys with the battery plugged in one of the Ys and two servos in the other two plugs, still no cigar. A single works, two do not work.
I am using 4 cells, nominal 4.8volt pack, charged, no regulator.
These are the servos that were reworked by the factory so as not to lock up, or whatever. They have the sticker.
I am ready to try any other reasonable test you want to try, Mike.