I tried a C&D with the 737 Max and I can’t engage the external power supply (GPU). Explanations: I remove the covers and leave the shims (normal), I enter the cockpit, I activate the batteries, I ask the ATC for the GPU, the ATC sends it, the GPU arrives and connects but in the cockpit on the overhead panel the GRD PWR does not light up and does not activate when I switch to ON.
The GPU connection on the Max is broken. I haven’t been able to get GND power working yet. There is usually a GPU sitting there when I launch a flight at the gate. The blue ext power “available” light is on in the OHP, but the switch currently doesn’t turn ext power on.
I work around this by turning on battery then powering up the APU instead. The APU on the Max takes a while to start though so be patient. There is no gauge for the APU like in the 737 NG. The only indication if APU activity is a APU orange warning light that appears on the cockpit dash. The blue APU avail gen lights should eventually turn on in the OHP so you can turn APU gens on. I add a bit of extra fuel in to compensate for the APU running for longer while I set the aircraft up.
I raised a bug already for GND power being INOP on the max.