The Mark 2 was their 1969 model. Some things just don't last 50 years.
If the last 50 years of upkeep has not been done, good chance it won't work until all of those chores have been caught up.
Age and mileage both count. Even if it were a 'barn find' with 500 original miles you would expect the filter capacitors to have failed from age alone. Every electrolytic capacitor in it should get changed. You can try replacing just the ones that check bad, but first you need a way to check electrolytic capacitors if you want to go that route. Replacing every, single electrolytic cap is the only rational approach. When I said "power supply" I meant the parts in it, not the whole thing.
But there's more. A radio that was used a lot will have worn-out tubes to deal with. No odometer to read the mileage from, so this part of the picture is fuzzy.
The PA/CB switch has everything in the transmitter passing through it. Oxidized contacts in that switch alone can shut it down. Same goes for the tube sockets. Cleaning oxide from the tube-socket contacts and the tube pins helps if this is part of the picture.
Last, you can't easily find out how many of the channel crystals are dead or off frequency until you have spent a bundle of money to make it transmit again. How big a bundle? Again, depends on mileage as well as age. Might have five bad crystals. Might have five good ones. Or less.
The relay has been out of production for decades. The types you can still obtain won't fit the original socket. Good news is that a new socket to fit relays you CAN buy will fit in the same size chassis hole. But the wires do NOT go to all the same lug positions. The new relay has the pins wired in a different pattern than the original. Once every ten years or so we see one of those relays with a bad coil, prevents it from going "click". But it's that rare. A relay that won't go "click" is nearly but not always because the power supply has become too feeble to power it, or the mike has a problem.
Nothing easy about the Mark 2. This is why anyone you can talk into servicing them wants to charge a bundle to do it.
Enough rant for now. With any luck the receiver still works.
For now.
73