Well 7777 Is right on the code -1 on display is a brake switch input is missing check switch on slave cylinder. The code H and L on contoller H means to run learn normally after a firmware chip has been installed or something erased the memory from the chip. L means learn mode is in progress. Are the codes flashing one after the other ?

polecatizzy,
I am assuming is the same unit you have started an earlier thread by stating the unit won't go up & down unless you hold the contactors in. It is always a good idea to keep all the issues in one thread to get a faster resolution to your issues. Readers won't necessarily look for your other postings. And a machine serial number is always very helpful for getting you the most accurate answer for this machine.
Guys like 7777 & EdwardT, Duodeluxe and many others are very helpful & their advise is "free" and sound - they all have at least a little gray hair and scrapped knuckles and know what Jesus pin is.

If its a GE system, seat switch, (foot switch) is not operational. Check for pulled wires, broken switch, ect.
If your getting an E01, then the L/S drive motor is over heating, but you have an order picker, right? This only has 1 drive motor, so it doesn't apply.