Like the others said make sure your H-bridge contacter (f/r) is functioning correctly, n.o. And n.c. Assuming your contacter is fine you need to check for B+ input from your direction switch at TB5 on your ev100 card. If you have it I would suspect the card is bad. If you don't you have a wiring issue. Reman ev100 cards are cheap, I'd call your local forklift shop and ask for a price, they may ask for a photo of the silver tag on the top of the card. Here is a link for a GE manual (public ) https://shop.fsip.biz/Image/GetDocument/en/80

I would look at the contractor that is working when it is in the backseat position it is possible that it is not making contact with the tips this would not allow the contactor that is not working to drive in the other direction

Check the tips of the contactor. If it pulls in but no travel it usually means that the tips are not allowing current to flow either from pitting or from being worn. Depending on what type of contactor it is, you can either get a tip kit or replace the entire contactor assembly.