3rd brake light/blinker/abs light
 

Last week my abs came on and the speedo on occassion acts funny.. now i know from reading the forum that this is most likly the sensor in the rear dif... but last night my right blinker when turned on just stays lit and the rear 3rd brake light is also lit when the headlights are turned on... if you turn on the blinker the 3rd brake light also turns off.. any ideas?

Could be the Multifunction (turn/wash/wipe/hi-lo) Switch. It can give a variety of strange symptoms when it goes bad.

where is that located.. any chance it could just be a bad bulb or fuse?

I just went out then to wash the truck as its mild here today for a change.. and the blinker/ brake light are fine again... i wonder was it the cold weather... ice build up .. condensation? trailer hitch plug maybe?

If it were a fuse, things would be off at the wrong time but you have stuff that is on at the wrong time. If it were a bulb, I don't think it could make the third brake light come on with the turn signal.

Bad grounds can sometimes make odd combinations of things happen but your symptoms don't seem right.

The Multifunction Switch is the combo switch on the left of the column with turn signals and hi/low beams. I thought it might be that because it controls the brake and turn signal logic and has headlight functions, too.

Just to confuse the issue some more, here's another idea. The taillight/brake light/turn signal wiring and the ABS/VSS wire all go through a common connector that sometimes causes multiple electrical problems. It is a large 40-pin connector below the driver seat and is accessible only from under the truck.

Unscrew the center bolt, open it up and look for water or corroded terminals inside. Even if there is none, it is good preventative maintenance to pack this vulnerable connector with dielectric grease, available at Ford dealers and auto parts stores.

Your truck may possessed.... if it's not that I wouldn't have a clue.

well Bob, maybe it is the connector under the seat or maybe it is the multiswitch.. everything is fine when the headlights are NOT turned on.. as soon as you turn on the headlights.. thats when the problem occurs

I have still havent found the source of the problem.. All the Bulbs seem fine.. the only thing that i do notice is that when the lights are turned off , the drl's will flicker from time to time.. but as i mentioned when you turn the headlights on.. the right blinker wont work , and the 3rd high mount brakelight stays on at all times..

I really wifh i knew what it was

well the weather was fine today so i looked at the trailer hitch plugs, the plug under the chassis (under the seat) and took out the rear taillights..cant seem to find the problem.. I guess the only ohter thing it could be would be the headlight switch? how can i tell?