i would check for a bad ground first. Use an ohm meter, the connection could be resistive.
2008 F-450 Lariat loaded on order 7/3/07 delivered 9/13/2007 Pueblo Gold and all the goodies except Nav radio and moonroof and Fisher 8'6" X-blade
F-350 Lariat LOADED CC SRW LB 6.0 SOLD
Med. Wedgewood Blue
All Options except moon roof
8'6" Fisher X-blade SS
2003 PSD 6.0 Lariat CC SB SOLD
All options but the moon roof