D2 24V elec start problem

I don't think so unless somehow when you connected the tender, it was energizing the solenoids but I doubt it. You can test the solenoids initially just by seeing if they make a "click" sound when you energize them. If they don't, use a jumper to go straight from the 24v to the terminal to see if the problem is in the switch circuit. If it does click with the jumper, your switch circuit is faulty. If it doesn't then connect two spare 12 batteries together (can just use jumper leads and attempt to energize the solenoids. Basically just work through the system like that until you find the fault.

you can check the coil winding in the soleniods with a continuity test on a multimeter (disconnect the power feeds first) if they have continuity then the windings are okay. then you can add power to the solenoids to get them to close and see if you getting power on the load side of the solenoid if not its bad go to autoparts joint or autolec and get a new one.
these are generic ones so available anywhere and fairly cheap also they tend to last a long time too.