How do you test a cuda road lamp switch?

Well it is an on off switch with 2 terminals. Basically an expensive SPST switch. Single pole single throw. You can use an ohm meter, but there is no load.

The switch turns on a relay. Wire up a device with a small load. Make sure switch does not get hot, indicating corrosion or dirty contacts and higher resistance. The switch does not need to be grounded. Hot from power source on one side, the other side to the relay/ load.

What Nanket said, start with ohming it cold & see if it does basic on/off. More info on what is going on & what is pointing you toward that switch

I am doing a restoration just wanted to see if the switch is good before I install it

Alright, makes good sense.

I would suggest taking the switch apart and clean the old grease out and re-grease, very simple process that can be done in 5 minutes.

No need for load, use DMV set to Ohms,
Should be open or short across the terminals as you switch it on/off

Agreed, if it will come apart I would sparingly regrease the sliding parts & clean the contacts.