Bad Controller or micro-switch ?

[J.D.Y.]

I have, as best I can tell, a 1990 Marathon,36V electric ( 3 wheeler). Had it for 10 years and never a problem. Put it away last winter, running fine. This spring went to drive it, it rolled about 20 feet and quit. I had left the charger plugged into it all winter so it could charge as needed. I noticed that if I pressed the accelerator I would hear the solenoid click, at about half position the cart would shudder forward ( same in reverse) then "kick out" and not move. I checked voltage across the batteries and had approx., 38 volts.
Next, I checked each battery individually and found 2 were < 2 volts.
I replaced all 6 batteries with NEW batteries. Still the same problem.
Read online how to check solenoid & did so. "IF" I did it correctly, the solenoid seems to check out OK. "Clicks" in F & R, showed .04 ohms, etc.
Noticed with meter on CL+/BL+ and CR-/BR- , with fully charged batteries, if I step on the GO, key on in forward, voltage drops off to near zero. Let off the pedal and the voltage rises back up.
While it appears the charger is good, when plugged in, the meter shows no Amps, but the charger does not kick off and will run continuously.
Finally, with the charger plugged in, if I turn key on, press go, the cart wants to run, then charger kicks off, let off pedal and charger kicks back on.
Have checked, cleaned and tightened all connections.
Anyone have any ideas and /or if this is indicative of a specific component failure ? Last resort I'll take it to the local cart shop where I bought it. Just hate to if its a simple component I can switch out myself. Thanks.