The fuse was originally 14 amps.  It is marked on the side of the radio.  Originally the car was 6 volt positive ground.  The radio will work either positive or negative ground unless the vibrator has been charged to solid state.

Bill A
ClassicCarRadioDoctor.com

Yep looks like the radio doesn't work, there's a faint glow in the filaments of the tubes but that's about all I saw. Someone above said that the lighting wire attaches to a terminal near the radio, I looked around and I couldn't see any obvious connector, is it the terminals above by the speaker?

An AM radio tuner is very sensitive to the actual length of the antenna. If you change the expected length it will reduce performance in sensitivity. There is a trimmer capacitor to "fine tune" the antenna once the radio is installed in the car. Likely found on the back of the chassis.

Once the antenna is hooked up tune a weak but steady radio station somewhere around 1400 kc on the dial, and peak the signal with the trimmer for maximum loudness.

I had my stock radio converted the AM/FM/ Bluetooth etc. and it still used the same plug in so I’m guess yes. I did need to use the same Original style connectors to the light and power under the dash.

56 Vic, B'Ville 200 MPH Club Member, So Cal.

Will a modern antenna connector work on those old radios or is it a whole different connector? It's been awhile since I saw my Ford radio, I'm planning on taking it out tomorrow.

https://sc02.alicdn.com/kf/HTB1YruTSVXXXXaRXpXXq6xXFXXXm.jpg

I tried that first... didn’t work very good so l mounted under the passenger door.

56 Vic, B'Ville 200 MPH Club Member, So Cal.

Thank you very much for that info, very helpful!
I wonder if a tiny little antenna like this fitted sideways underneath the dash would work okay.
https://www.ebay.com/i/223571819301?chn=ps&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&itemid=223571819301&targetid=883484275562&device=c&mktype=pla&googleloc=9023247&poi=&campaignid=9343999134&mkgroupid=101452701304&rlsatarget=pla-883484275562&abcId=1139336&merchantid=6296724&gclid=Cj0KCQjwzZj2BRDVARIsABs3l9LxpjPJqggigvrBEIR6SJRyjpbkNZu25BBBZzKqLY1UOJ3IBV7AifsaAqU8EALw_wcB

An AWG 16 is plenty for a radio feed and a 7 to 10 amp fuse maximum.
I’m not sure on a 55 but my 56 had a grommet hole right behind the hinge on the right side for a fender antenna. I did not want to drill a hole in my fender so I made an angle bracket and mounted a stock style antenna below the passenger side between the frame and body edge. I used a loose fitting zip-ty near the end to keep it from touching the body mounting. Been there 8 years with no problems and good reception.

56 Vic, B'Ville 200 MPH Club Member, So Cal.

Thanks for the link, very helpful! Does anyone know what kind of fuse the radio would use though? Also what gauge electrical wire?

Most likely you will have to replace the vibrator use a solid state one you will get better results the tubes might be bad but the old vibrators usually are an issue. You should hear a low buzz or hum when you turn on the radio .