2017 3791RD furnace issue

[usaf_retired]

Been troubleshooting furnace issue. Furnace works ok when jumping the 2 blue thermostat wires back towards the furnace. when I wire it back to normal i'm having a 12 volt power issue. It sometime has a delayed start after requesting heat. Blower will start up for about 2-3 seconds then shuts back down. blower might try to start up again, then does the same thing...shuts back off after 2-3 seconds. It's like it's not getting a steady 12 volts. I went on top the RV (rear unit) to check wiring up there. I cleaned the furnace connection to the ac control board...no help. I put a new Dinosaur control board already. called Dinosaur tech line. He says there is corrosion somewhere causing it. Anybody have a idea what the trouble could be? Thanks