The heating grids in the seat bottom and back are typically wired in series, so a break anywhere will totally disable the seat heaters. It's not clear whether you tested for continuity across the heaters as well as for power.  Assuming you have power, most frequently the problem is going to be a broken wire in the seat bottom heating grid. (There is probably a thermostat in the seat as well that is used to regulate temperature and that could have gone bad.) After going through this several times I finally got tired of taking the seat apart to keep fixing broken wires so bought an aftermarket seat heater that straps to the seat and plugs into the cigarette lighter.

Check the actual plug in wire connections under the seat.

Checked the plugs today. All ok.

Thanks for the comments Joe. I am trying to get info on which wires are which in the plugs. I do not have any wiring diagrams.

Thanks again Joe.