pro;
Is the truck's chassis electrically clean? Has the brake circuit been ck'd for short circuit or has the brake pedal been ck'd for adjustment? What are the readings that you are seeing at CH1,CH2,CH3, & CH4? Have you looked at the plug and socket that are directly below the battery for voltage leakage? What is the truck doing or not doing?

Board has been replaced and still only has an output of 9.2 volts. What other reasons could keep the voltage output down on this system?

Pro;
If the board isn't physically burned up and Nissan local dealer can not supply one, may I suggest sending it to Flight Systems out of Mechanicsburg, PA and see what they can do with the 10 Volt power supply print board you have.

Yes that is the one. Right side of truck smaller board of the two

pro;
Are you looking for the sub - board that is located on the panel just to the left of the main board, or are you looking for the sub - board (CR board) that is mounted just above the main fuses. No. 1 print board B 29381-41H00 and No. 2 print board C 29383-41H00.