Rear passenger taillight won't function on turn signal or brake

Hi @rreyes13

You said "Also checked connections with a volt meter and everything seems good..." I assume this means that there is voltage right up to the turn signal/stop light LED inputs in the lamp assembly is this correct?

If so have you checked the earth connection to the lamp assembly with an Ohmmeter or connecting a lead from the chassis (good clean bright shiny metal earth point) to the earth connection of the lamp module to see if they then worked OK? No earth = no current flow through the LEDs to light them up when voltage is applied.

Often what happens is that the common wire (the 'Earth ' or negative wire) which is common to many items in a car and usually connected to the car's chassis, does not make proper contact because of dirt, loose connection or rust. And even though you can obtain a voltage reading, under load and drawing current, the 'rusty' connection may present such a large resistance that there is just not enough current to drive the item under question. Note that a 50W car lamp can easily draw 4A plus and even though LEDs draw small currents, they are used in large numbers and are of the hi- bri type needing 20-50/70mA each.

Thus, try cleaning/removing rust, dirt & grease from connections associated with the item, then solidly tighten the connection(s).

Sounds like you have a ground problem on that light housing. Try running a jump wire from a known good ground to your socket or housing, if it lights up then you found your problem. Also does the truck have a trailer light plug? Those can be the source of many rear light problems as well.