We have a Case 586H rough terrain forklift that was purchased new about 11 months ago. our problem is the when you put the FNR shifter in forward or reverse the brake light and alarm comes on. When it first happened the dealer picked it up had it for three weeks and couldn't find the problem. They say they aren't sure where to look and we can't do without it for another three weeks.
Pretty sad to hear stories like this...... If it's under warranty they can pay a sub-contractor to carry out the repair. I would try to get a hold of a wiring diagram & pay a good auto electrical tech to look at it. Hopefully, it would get repaired & then ask the dealer to then reimburse the cost.
Do you really need the backup alarm? Could you just snip the wires?
It would help if you could tell us what brand of powertrain you have in that machine. A pic of the FNR lever would help to. It is definitely an electrical issue, but could be cause by a faulty sensor.
I guess I should have noted that the alarm isn't the back up alarm, but the in cab warning buzzer and the park brake light "(P)"