I have a 1998 F150 XLT. 3 times in the last 4 days, my headlights have suddenly gone dead, 2 times it was like less than 3 or 4 seconds, one time it was like 10 seconds. I can't recall if the dashlights went out also, something a car-savvy friend asked me. All 3 times are within the first few minutes of driving, and 2 of the times were at the same place, turning right at the 1st road after leaving my subdivision. A car-savvy friend suggested maybe one of the relays under the hood(okay which one since it's not in the owners manual or labeled on the box.) But searching this forum the MFS (multi-function switch) may be likely. Any ideas? I have no qualms about taking out the MFS and cleaning it, but first thought I'd solicit ideas. Thanks.

 

The dash lights are serviced by a separate set of terminals within the light switch than those that service the headlights. If the dash lights do go out, your intermittent open circuit is at the input of the switch assembly or prior to it.

Fox-body Mustangs were infamous for having headlight switches go bad , leaving the driver in the dark. I don't know if the F150 switches have ever shown such a pattern.

Were your lights on low or high beam when they went out?

This is from the 97 EVTM. I don't have a 98 edition.

The output of the light switch goes to the MFS where low and high beam are selected. From there, high beam power goes through a single fuse (20) in the fusebox out to both high beam elements and to the HIGH dash indicator (also the DRL module, if equipped). The low beam power goes to the fuse box, is split into two branches, each with a 10A fuse, then out to each low beam element. The right side low beam also goes tot he DRL module, if equipped.

Checking the headlight and MFS switch connectors for overheating or other evidence is a good place to swart.

Steve

 

I had low beams on, and again hazy on when it happens as I was trying not to crash into tree.

 

Definitely look into the headlight switch... had that happen to my 93 T-bird. If memory serves correctly the new switch was like $20 at the parts store?

 

Well, my headlights going out got worse, so I had to do something about it. I bought a multi-function switch(MFS) on ebay for $18 for a 1997 Ford Ranger(well it was close to my 1998 F-150!!!) and installed it. Now it works fine, although I noticed the angle of the whole switch is a little lower than my original switch. Oh well, I took time to take apart switch to see if corrosion was the problem. It sure looks like a lot of corrosion!!!