Nope the wiring is good as well. I did everything mentioned. My mechanic I have for things like this couldn't figure it out either back in November.

 

It has to be in the wiring, what do you think powers them? There has to be a broken connection some where.

Search this site, it has all the service manuals in pdf form.

This pdf is for the Parking lights and others.

Ford Service Manuals - DIAGNOSIS AND TESTING, Rear and License Plate Lamps.pdf

 

This may require a trip to a Ford dealer, and the use of their magical scanner. If the fuse is ok, there is a good chance it is a problem with the SJB.

 

I know wires power them obviously. But I checked the front ones and wires are fine. The rear I will check tonight. I'm fustrated as I know how to fix electrical....only when I can locate the problem. Why is it only my Mustang that is having this problem. Oh thanks for the wiring diagrams btw

 

Ugh SJB replacement is way to expensive so I hoping to avoid that. It's funny because 10-14 and the new S550 use the traditional fuse box from what I heard...I wonder why

 

SJB woes are not that un-common on s197 cars. When they act up, al sorts of weird stuff can happen. s197 Mustangs also had water intrusion issues (particularly the '05-'06 models) that could cause electrical gremlins.

Google s197 sjb, or water intrusion, and the results should give you a bit of reading...maybe even a few ideas on other things to check.