Before considering a replacement flex circuit, make sure the housing that supports it hasn't melted and deformed behind the bulb holder contacts - especially on the brake lamps. The only taillamps I've needed to hard-wire as a last resort suffered from this melting.

It is one of those tail-chasing syndromes; the cracked lens admits water, the moisture corrodes and degrades the contact, the contact overheats, the spring tension deforms the soft plastic behind the flex circuit, the contact pressure relaxes, resistance rises, the heat increases, and so on. The same problem affects the fold-over part where the harness connector attaches.

I tried to photograph the distortion in the once planar surface by looking toward the edge.

Bulb holders - can buy new from fcpgroton, if I recall correctly.
Stamped circuit in taillight housing: Get from junkyard.
Can also buy new taillight assy. from fcp, but costs. 245 version was $80 ea., IIRC.

Also can use emery cloth, knife blade or whatever to clean contacts.
Can bend springs as neeed for better contact.