"I was told a couple weeks ago on Fordbarn that Bosch makes a good one but never found a 6 volt one."
Early 1950-60 VW uses them:
Bosch SPDT
6V 30 amp Relay
0332204001
Used as dimmer relay
In 1950 to 1966 VW
Also listed as:
Merced 0035340245
Porsche PCG61510100
John Deere AR91168