I would guess a 4 wire would be one wire for flasher input, one for pilot light, one for both left lights and one for both right lights. If so it needs a 3 prong flasher it you want the pilot light to work.

This tech tip tells how to determine what wire is what.

"It's just a phase. He'll grow out of it." Mama, 1964

1956 Chevy 1/2-ton 3100
1953 Chevy 6100 "The Yard dog"
1954 GMC Suburban Now with a new proud owner.