Awesome, thank you!!

Part number for the master cylinder is 082812

And it was in fact the switch I thought, replaced it, all safety systems back in place and lift running perfectly, now just have to find a part number for the brake master cylinder so it's no longer a double-pump to stop braking system. The previously professionally diagnosed unusable battery hasn't been on the charger for over a month and still showing 90% charge on the meter when I used it for about an hour this morning.

So after lots of wire/circuit chasing with no service manual I think I have narrowed it down to one of the micro-switches on the accelerator assembly. This would be the switch that sends power to the forward/reverse selector. I have bypassed every other switch (one at a time) with the same results. However if I take and put battery voltage directly to the switch the contacts instantly engage and stay engaged till I put the selector back in neutral.

I have a new switch ordered and hopefully this fixes the problem otherwise the next step is to call in a mechanic or wrecker, jury is still out on that decision.

According to the label on the card it's an EV-1

Is that a EV1 or EV100, they're different.

I think I may have found the problem,

According the the schematic for the EV1 I see nothing to drop the voltage below battery level at the forward/reverse switch which in turn is the positive side of the contacts. I checked the voltage at the switch and it's showing 28 when the battery is at 37 so I ran a wire from battery voltage to the switch and as soon as I select forward or reverse I get full engagement of the contacts and lift runs perfectly.

So without a service manual I can't know if this is the problem but based on trial and error I think I'm headed in the right direction.

Opened up the back panel where the controller is located and first thing I find appearing to be out of sorts is a wire connected to the terminal block on the right side of the controller, running across to the left side then just tied off to another bundle. Doesn't look like it belongs there.

I'd happily post pictures but can't seem to navigate my way around that subject within this forum.

Perfect, thank you, will take a look at it.

Control card is at the very rear of the lift, behind the rectangular plate with the Crown logo on it. Search google for 'Flight Systems EV100' and you should turn up some info on the control system and testing procedures. Try disconnecting the battery and then unseating and reseating the connectors into the control card. Check potentiometer voltage at the control card. There is a large capacitor in the back which will give you a nasty belt if you touch the terminals, even with the battery disconnected so take care.

Adjusted the pot, doesn't seem to make any difference. Checked all wiring from pot/switches to the terminal block under the seat and everything checks out with 0.0 continuity. Stumped as to where to go from here, don't know where the cards are or even what they look like but the symptoms at the contacts remain the same both forward clicking/buzzing/chattering when trying to move straight ahead. Same symptoms on the reverse contacts when trying to move back and turning the wheel lock to either side causes just one contact to act up.

So with my limited electrical knowledge it would appear that the failure in the system is somewhere before the signal divides for forward/reverse/turn. I checked the common going to the forward/reverse selector switch which showed perfect 0.0 continuity terminal block to switch. Checked the signals from the accelerator pedal back to the terminal block and again clean signal from the pot and clean switch off/on/off on the 2 switches.

Looks to be deeper in the system than I have the ability to track down without schematics or a service manual.

Ev100 old sc, first you're direction lever selects direction, the pot old solder style under footpedal selects speed, at the card 3.5v to zero at full speed, and the switch by the pot tells the cards, you're travelling.
There are also switched underneath for steering that can effect travel, that's why with two drive motors there are two sets of contacts.

I have the cover all off, have looked over all 4 contacts for forward and reverse. They don't appear burnt or out of sorts on the tips of them and in fact when they are clicking it's both at the same time on forward or reverse. I suspect the issue may be in the pot or the switches under the accelerator actuated by the gear inside the accelerator housing.

I will adjust the pot tomorrow and move forward from there. Would one of these switches giving a dirty signal instead of a clean on/off cause this type of symptom?? I checked them with a simple ohm meter but previous experience on other switches tells me that just because the ohm meter says it's working it may not be working correctly.

When you replace that pot you need to adjust it. 5 ohms right before the accelerator switch makes up. But I think your main problem is contactors. Remove the cover just behind the floorboard and check out the tips. You can try to drive the lift while looking and see where that buzzing is coming from that is usually from the drive motor getting some power but not enough to move. Their a lot of components behind the back panel but these usually will make the lift just not work or give very specific symptoms like trying to move and it jumps 1 or 2 times then cuts off. If the contactor tips are burnt all to crap (you will see the 2 that move one for forward travel another for reverse) Sometimes you can take them apart and use a file and lightly resurface the tips, keep in mind these need to make almost full contact to it's mate.
The tip should be a small dimple like mound if its just burnt to where their no dimple left the you would need a contactor kit to rebuild it. If you take this apart then mark cables and take pictures to ensure you put everything back in the right place.
That is just a EV operating system and fairly easy for experienced techs well us older people anyhow. I'm not sure what you call a lot of money one option would be to call and get a tech to look at it if you have no account it will be COD before he leaves meaning a call to the branch and a CC number. You could tell them you need a detailed quote from their and buy the parts yourself and replace them. Make sure to get with the tech and have him show you just what he found so you will know were the parts go.(could be as simple as a loose wire) For that operating system it should just cost the travel time to get their and no more than a hour to find the problem a good tech might find it quicker.
Or you can keep posting back and I will help all I can been working on them for 25 years but it's hard to go much further than the contactors without being their.
EDIT. On the contactor coil their 2 wires these are screwed to the coil on these old trucks make sure the wire is secure and tight, just unplug the battery before you try to remove anything or check for loose wires.

Just went out and checked it, 39.1v resting just off the charger, 39.1v when turned on with steering/tilt pump running and 38.2v when lifting the mast. Erratic drive, started off fine then in a couple feet started the clicking/buzzing and lack of response to pedal but voltage stayed pretty steady 37v to 38v the entire time, no spikes or dips.

Well first you need to check the battery under load and see how far the volts are dropping. Simple test check the voltage while raising the forks, report back with volts when turned off and volts when raising the forks. That is probably your problem but could also be contactors.
Electric lifts hate junk batteries.