Truck, before finding your post, which seems more relevant, I added the following to another:
"The unit won't power on. Appears as if it's not getting any power at all.
The old batteries were surely bad. They were very hot, and one of them read 0 Volts, ie, completely discharged; shorted internally, I'm thinking. The other batt read 6.6 volts.
I installed two new batteries, thinking the unit required good batteries to power on, but apparently it's something else.
Can't see any physical damage inside at all. Nothing appears burnt. The two 40A fuses on the main board are both good.
My only test equipment is a multimeter.
Any ideas before I trash it?
Let me confirm the right way to connect the batteries. I connected the negative terminals of the batteries with the short white cable. Then I attached the red and black cables from the system board to the positive terminal of each battery. (In parallel, as I understand it.) Right?
Hope you can confirm the wiring. And hope I connected the batteries wrong, which correcting will fix my problem.