Gentlemen,

I have a 1999 F-150 4wd auto with a 5.4L. I discovered a grey colored coonector branching off the headlight and side marker harness on the passenger side in front of the washer fluid tank. It is a 4-pin connector and I cannot see anywhere it should be connected. Looks to have about 20 ga wiring. Any help would be appreciated.

Thanks

 

you have fog lights, how long is the lead? , both lights?

 

Nope not for the fog lights. They are connected and working. This connector is only on the passenger side

Thanks

 

block heater? they usually have an outlet to plug an extention cord to but maybe it requires a special cord

 

On the '00 and '01 shop wiring schematics, there are only two possibilities. The washer pump or AC pressure cutoff switch. Check that these are working (or if you don't have AC that would explain the extra conector) Also, make sure it is not your corner lights and that both headlites work.

I did however find one illustration that showed an extra unlabled conector. Perhaps it was for something in a previous year and Ford switched wiring harnesses mid-year.

 

Washer pump, AC pressure cutoff, corner lights and headlights are all operative. I gonna accept the extra unlabled plug as a block heater. The wire gauge seems to match that explanation. Thanks to everyone for the input.

 

That is wired directly to the block heater, no integration into the factory loom.
20 AWG is way too light a gauge for resistive heating, mine is 16 AWG, and is only wired tied to the loom on the driver's side. Same with my 2001 SCrew.