04 379 marker light relay

Hi guys I'm having a problem with my marker light relay, it keeps going bad I think there is too much resistance being built up since the top spade terminal looks as if its melting by the plastic, its a napa ar143 relay which I believe is 20amps. The problem started when I replaced the relay, I took a relay out from another position and got that one not thinking it could be different. The truck has no fuse panel cover with the picture of all relays and fuses. Does anyone know off hand what size relay I should put in there? any help is appreciated thanks!

 

Its an 04 379 last six are 813048