Three years ago I installed a Thetford Tecma toilet in place of the Vacu Flush. I used the existing power wire which was only 12 gauge. I knew it was smaller than what the manual suggested, but it flashed fine most of the time. Had more issue when not plugged in because voltage is a bit lower.
Well, a couple of weeks ago I ran 8 gauge wires to the toilet and it flashes much better now, especially when the coach is not plugged in.