I bought my 1973 c20 3/4 ton chevy and the blinkers don't work only thing I replaced was the flasher how do I repair it to be able to work? I don't know where to start

Check the bulbs and fuse. Also clean the light bulb sockets and electrical connections.

Full_of_Regrets is spot-on. Aerosol electrical contact cleaner works well. Copious amounts, spray the stuff everywhere in the bulb sockets. Otherwise fuses.

Ok if that doesn't work what would I have to replace or upgrade?

Do the 4-Way E-Flashers ALL work? On all 4 corners?

Check to make sure wires to the tail lights are not damaged. Re- wiring the tail lights will be fairly easy to do should nothing else work.

And hold on...geez, wait, I did NOT mean spray contact cleaner in the fuses and/or fuse box. I worded that poorly

I didn't get to the flashers I was occupied by the GPS they have in it. I checked to see if when they put thag in if it ruined something.

I like to use rubbing alcohol on a Q-tip for cleaning contacts. Just wait a minute or two for it to dry.

Here we go. A 1973 will not have factory GPS/navigation. It's aftermarket, probably Garmin or Tom-Tom. Nothing wrong with either if those ..... but if somebody tried to make a permanent power supply, instead of using cig lighter, they may have cut some wires or tapped them to get power

If the dash lights work then the problem is not the fuse as the dash lights and tail lights are on the same circuit.

I meant the dealership put it in there and they will take it out after I pay it off

Everything seems to work dash lights and everything but the blinkers

Ahhh... different thing. They want to know where the car is. Who knows what/how they did that