I have a '98, is there any way to wire my cargo lights so that when I put the transmission in reverse they come on as well as the back up lights? Thanks for your help.

 

Yes, you could do that

The cargo light is powered by a Black/pink stripe wire that runs in the harness with the Dark Green cab brake light wire
But not sure where that runs down the inside of the cab and up to the dash
Best guess would be it comes in behind drivers kick panel, but could be passenger kick panel as well
It runs to a connector on a relay above gas pedal, its not relay activated though, its powered at that connection by the Dimmer wheel which activates the relay for the dome light

And the Reverse light wire is ALSO Black/pink stripe where it comes out of the Reverse light switch on the transmission and runs to tail lights

So if you cut the Black/pink wire going to cargo lights and spliced that to the black/pink wire going to Reverse lights, it would come on when trans was in Reverse

You could install an on/on toggle switch in the cab where you cut the wire so cargo light could be used as is and in Reverse

Reverse lights usually have a 10amp fuse, which is a higher rating than needed for 2 bulbs, thats for trailer hook ups, so adding the cargo light bulbs wouldn't be an issue amp-wise, even better if you swapped in LED bulbs

 

Using a relay you could keep the cargo light functioning as stock, but have the cargo light come on when transmission put into reverse.

Must use a 5 pin relay that has an 87A terminal

Cut the Black/pink wire somewhere between the switch and the cargo light
Connect the end coming from the switch to terminal 87A
Connect the other end of that cut wire, the one that continues on to the cargo light to terminal 30

Tap into the Black/pink wire from the backup lights and connect it to terminals 87 & 86

Connect terminal 85 to ground