yep its either the brake switch or start switch
(and as was mentioned if there are any other safety switches inline with the start circuit)
A handset would be of great help for sure...

start at the terminal strip terminals, wires 6 and 8 i think are the fwd and rev inputs. (TB5 and 6) TB4 would be keyswitch and TB1 is accelerator input.

and of course check your wiring , connectors associated with these circuits.
Also a truck wiring diagram would be helpful.

I would have to agree 100% with what Edward T said.

So if you have access to the truck wire schematic that would be helpful. The EV100 looks for the same inputs no matter where it is used but different manufacturers use more or fewer switches in the circuit. At minimum you are looking for a park brake switch, pedal brake switch and start up switch in the accelerator. Some may use a seat switch forbtravel only and some may have incorporated a seat belt switch. If it is a man up unit(like an order picker) it may also have a chain slack switch. Once you have determined what switches are in the circuit and how they are wired a volt drop test starting at the switch furthest from the card and moving closer may help determine your problem.

houw i ken sent you2 pdf files???????
it is to bick voor mail

Also you might want your company to invest in a ev-100 handset as it can be used as a dignostic/ parameter checker changer thingy. In other words it would certainly not hurt the cause LOL.

I think you can download the manual these days, from Flightsystem's website, but the real answer is to check the inputs at the term strip on the card.

Can you get your employer to purchase the Flight Systems Service Manual??