Tail lights 1994 GMT400 Chevrolet CK2500

[bmcutright]

My dad is having trouble with his rear parking lights not coming on. Turn signals/brake lights/backup lights all work. He thinks it has to do with his homebuilt wiring of a 7pin trailer hitch decades ago. Wondering if anyone has suggestions.

 

[Chris JW]

test the plug with a 12v testlight or voltmeter and just keep working your way back( it appears to me that the 12v may be either black or red and the aux may be the backup lights)