It could very well be the problem. Why don't you try testing from the (+) of the bulb socket to an inside-the-truck screw into the body for (-) and see if you have 12vdc. Or, you could try testing continuity from the bulb socket frame to the chassis (or body) and see if you have a good connection.

If the light control relay was the problem you wouldn't have a tail light on the other side either.

Frank

'89 [color:"white"]G-Raider[color:"white"] [color:"black"]Supercharged 3.0L, MegaSquirt 2, lockup A/T, 2.5" exhaust, 172k, Cibie H4s/Oscar SCs, Hella Micro DE fogs, Cobra CB, Superwinch hubs, LSD rear/Aussie Locker front, Bilsteins, Lifeline AGM, Rust-Oleum