Filter checks okay.
Q1 failed the E-C and B-C resistance check, 2.21 K instead of the 10-100K it should be. Confirmed enable signal to chopper module, it has not output.
Pricey mistake, VM, transistor and chopper module all need to be replaced and our 1 forklift has been down over a week.
I've added a couple pieces of metal to the lift and charger connector so that you can't plug the charger into the lift.

Does your lift have a filter block with the the fuses the unscrew at the top. Looks like a 3 inch block with some capacitors that are actually fuse holders.

Did the O14 test and resistance checks B-E C-E C-B on the transistor. Don't see any shorts, however did not get the 1 volt battery connected and 3 volt key switch on for the O14 test. I will check the O13 CCM enable switch next. Unlikely to be the Armature current sensor at this point as it appears there is no current to sense.

the erratic display on the new vehicle manager was probably because of a difference in software programming in the logic chip.
When you order one of those units they usually ask what features it has and want to know the serial number etc. Cat programs it before you get it generally. You may have been able to just change out the logic chip on the vsm along with the new power supply and it probably would have ran ok.
But now that you are where your at and getting the code 23 lets deal with that. Taking those apart is a pain and i'm sure you're not wanting to do that again :oD
So according to the troubleshooting guide Code 23 is:
Code Title - Open detected in Armature Circuit
Reason: During self test, proper current leverls were not sensed in the power transistor Q1.
System Response:
-1 Alarm sounds: Yes
-2 Operators Display: Code 23... inform service personnel
-3 PC Contactor: De-energized
-4 VFC Display: 23
-5 Speed Limit: 0.0 mph
How to clear: the key switch must be cycled on and off to clear this code.

Possible causes:
-1 FU5 may be blown
-2 There may be an open circuit in the drive motor
-3 There may be an open circuit in the power wiring for armature in drive motor.
-4 Power transistor Q1 may be bad
-5 The CCM may be bad
-6 The cable between the CCM and the Vehicle Manager may be bad.
-7 The Vehicle Manager may be bad.

Corrective actions and Checks:
- run tests -
--O14 - chopper control module PWM test
--O13 - CCM enable signal
--A11 - Armature Current Sensor voltage

I would definitely check the Q1 transistor, the surge from the charger could have also hit that as well through the vehicle manager when the operator pressed that contactor trying to get the truck to run. if you know how to run these tests from the maintenance mode then i would do that. And last but unfortunaly least, you may have to take the VM back apart and double check your connections inside it between the boards. Make sure you have all the cables connected to it correctly. they should be labeled and the connectors are db type connectors so make sure they are tightened down with the screws completely.

So new vehicle manager came in, power and display would flash off and on and strange LED displays on the VM. Swapped the power supply into the old unit and it comes up, all functions work except movement and I've got a code 23..

that is a good idea with the brackets on the connectors of truck and charger, actually most battery companies have these for sale. If you can make them thats a cheaper solution because they are not cheap if you buy them.

and about the power supply card, i was going to suggest checking that, it's what usually takes the hit and in some rare cases the distribution board or VFC.

I was able to get a copy of the trouble shooting schematic from the local Caterpillar dealer. The second section, key on before self test, called for 12 volts coming from the vehicle manager to the other boards. Display etc.. This was found to be absent. When I opened up the unit and had a look at the power supply that takes battery voltage and supplies the 5 volt logic and 12 volt power was not working. My follow up with the crew lead to the discovery that a mechanic had pushed in the contactor to see if the charger would pick up. That of course resulted in the higher open circuit voltage from the charger being realized at the power supply. The kernel of the problem was the operator plugging the charger into the lift instead of the battery. I've added metal brackets on the plugs for the charger and vehicle that interfere and prevent them from being connected. It still allows for a charger to battery connection.

Thanks for the helpful reply.

a full model and serial number off the dataplace would help alot more to get the correct information.

From past experience dealing with this situation i can say there is a high possibility that the controller or MIB might have been damaged.
Generally newer units have a protection circuit to prevent this but in older trucks this is not the case. Therefore any stored power in capacitors gets picked up by the charger and allows it to briefy detect the voltage and allow it to try and start up, that surge from the charger spikes the controllers and can over current these components and blow them out.
First knowing the full model number and serial would give us an idea of what system is in this truck.