Hi there I don't think this has anything really to do with it being a diesel but I got a 93 f250 turbo 7.3L and the passenger side daytime running light does not work. Also the passenger bright does not work however the driver side does. Both signal lights work and both lights work when the non brights are turned on just the regular lights are.

 

Check for power at the plug and work your way back to source of power ... Probably something real simple in most cases..

 

Okay thank you I will do that