i was checking the wiring diagram from the manual on the circuits and according to it , and this is fairly common with all EV100 systems.
The 1A circuit is controlled by the card, it gets it's negative signal from PB6 which is one of the plugs that plugs into the card on the end. Wires 41 going to the coil on the 1A contactor, on the opposite side of the coil is wire 10 getting positive from the handbrake circuit from what i can see.
The only other part of the control circuit controlling the speed is the accelerator circuit which is wire 29 to TB1 on the control card.
So if you are not seeing anything out of the ordinary with the accelerator control then the problem could very well be something wrong in the wiring shorting the 1A contactor circuit causing it to pull in unexpectly or you have some kind of issue with the control card itself.
I would be checking the wiring to the 1A contactor and making sure the wiring is not shorted against something and also checking the contactor itself to make sure it is ok, nothing broken in it.
If it jumps as soon as you begin to throttle it, sounds like you're on the right track with a bad rectifier. One of the 3 that have small control wires on them or the capacitor/s. This is a old lift? What does the control card look like? Any numbers on it?
Checked the switch and is working good. It will jump as soon as contactor is activated and right after use in low speed without having gone into high speed so switch sticking is not the issue. I'm thinking now it might be a rectifier shorting out from time to time. Not sure I don't have any experience with electric forklifts.
check the accelerator switch and see if it has a high speed switch in it, this switch controls the 1A speed so it can trigger the truck to use 1A speed when the pedal is pressed down fully so it will not be activated by the 80% on-time timer in the scr signal.
it could be the switch is pulling in prematurely causing it to jump into high speed.
Of course it could also be the 1A timer is set too short in the settings.