What started as an audible "click" is now turning into a head-scratcher for us!

Vehicle: 2001 Ford F-150 Lariat

Observations:

• First, we noticed a random clicking sound coming from the dash area. After some testing, it seemed to happen slightly more often when jerking the wheel left or right at slower speeds, or while cruising at highway speeds (perhaps caused by the shifting and vibrations of normal driving?). Clicking happened seldom to never while stopped. We noticed that when the clicking happened, the radio display dimmed and became brighter. (The sound resembles the sound of a relay clicking.) Passenger (wife) noted that it was behaving as if the headlights were turning on and off. Notes: The headlight switch had been in the OFF position (not auto, not parking lights, just straight up off) the entire time. Also, it was full sun outside (so likely unrelated to the auto light sensor.) Jiggled the switch a little bit, no change in behavior.
• Turned the interior light dimming switch to lowest. We observed a noticeable change in the radio display brightness when the clicking would happen, based on the position of the dimming switch. Assumption: The clicking was somehow related to the headlights being turned on and off, since the display was reacting to the dimmer switch changes when the clicking happened.
• Final test: Wife stood outside vehicle on sidewalk while I drove by. She observed the headlights were on, and then turning off (the switch was in the OFF position the entire time).

So the lights are clicking on and off randomly while driving.


How should I go about the investigation? Are there any other tests I should perform? Replace the headlight switch? Replace the multifunction switch (MFS)? Look for a loose ground or short (how?)?

 

I would suspect the GEM.

 

Quick update on this since the April 21 incident in the original post:
- We've driven the truck since that day, and haven't seen the problem since.
- I noticed that this problem had a lot of similarities to problems people were having with leaking windshields on F150s. Google would keep turning up those threads in the results.
- On that day the electrical problems happened, I do remember that we had spilled about a half cup of water on the passenger side of the dashboard. Tried to dry/scrape off most of the water. My current hypothesis is that some water got down into some sort of circuit/box, and was shorting out a connection. The next day, it was warm, so the water could have drained out/evaporated/etc. Haven't had the problem since.
- Now I wonder if that water has weakened the circuit somehow.

TL;DR: It's possible that this was all caused by a water spill on the passenger dash.

 

Could very well be. Electricity and water no likey.

 

I am sure it was possessed.