On the drive motors there is a small hydraulic line on each one that goes to an aluminum block along with a bigger hydraulic line from the right front side of the tandem drive pump and there is also a yellow wire that comes out of this block. What is the purpose of this block and is there a relief valve in it also is there a main relief or bypass valve that would be for both forward and reverse
left & right Forward and left & right reverse have their own reliefs. The bypass valve/tow valves are in the pumps, and would affect forward and reverse, each side respectively. See picture below. Is this question in relation to your last post, of weak drive? Your pumps were recently rebuilt? Attach some pictures of the valve/hoses you are wondering about
Most likely brake release solenoid valve, if the lines go to ports near the mounting flange. European variant I think?