Just a follow up on this one. The battery does drop down to 30 volts when under full load. I drove it for a bit, back and forth. Then started to turn the pump on and off alot while driving back and forth. Sure enough the code 49 goes off and shuts down. It did that a few times. So I checked the #5 scr connections and all was ok. I put a new #5 in and it did nothing to fix it. So then I thought is the pump contactor grounding or something like that. It has a external coil supressor (diode and 100 ohm resistor in series) connected on the terminals. Took it off and the resistor falls on the floor. It was broken. Checked the diode and soldered on a new resistor. The truck stopped doing the code 49 thing. Yeah.

before you do anything else, make sure you have a good [enough] battery, do 2 tests, ohms from the battery powercables to the frame of the truck, (must be more than 100k ohms,) and both "at rest" and 5 seconds full back tilt hydraulic stall voltages at the battery. (must not be less under stall than 90% of battery "at rest" voltage, 36.6v at rest no lower than 33.0v at full stall, but needs to start with a "hot" battery of much more than 36.0 v)

49 error code for the EV100 system indicates that it could be a possible scr 5 fault. I have had them in some cases when the snubber on the ev100 control system is the problem, however from what you have said while driving then activating the pump it seems to cause the problem, it may be that the more current draw is causing the scr to fail. So i would say possibly the thyristor is faulty. Before this though disconnect the logic plug and make sure that none of the pins are pushed back as a thyristor gate lead can also cause the same issue.