IIRC there is a vacuum sensor on top of the passenger side fender well, which will also illuminate the brake light. You could try unplugging the harness on that to see if the light goes away. If it does then it is one of a few possibilities. The vacuum pump may be going out or already gone making it difficult to push the brake. Or you could have a bad vacuum leak. If you have low vacuum this would also cause the cruise control to not work properly. One other possibility is the vacuum sensor could fail in the closed position indicating a false problem with the brake system. I don't know don't know how common the latter problem is, but I have had it happen to me. One last thing IIRC there is a sensor on the brake proportioning valve.

 

I'll check the sensors out, vacuum pump is working easy to operate when the truck is running I'll stick a vacuum gauge on it to double check

 

I just reread your post and wanted to double check and make sure I read it correctly. Are you talking about the instrument cluster brake light indicator or the actual break lights on the back of your truck?

 

I have seen a saggy parking brake pedal make the dash light come on.
Like dieselvein I am not sure what light(s) you are talking about.

 

If it is your brake lights, you may check that you do not have a crossed wire in the trailer plug if you have one.

 

the rear brake lights
have it to basic wiring at the back until I get this figured out
brake pedal switch is adjusted and lights stay on even with it disconnected
both wires to the brake light switch have power
turn signals work front and rear
hazard lights work front and rear
running lights work
Hi/lo headlights work
dash lights work
horn does not work haven't checked connections on the horns yet
wiper motor does not work, checked out motor is bad

glow plug controller is wired to a momentary push button
same with starter relay, done by previous owner

 

Try replacing your turn hazard switch. Do you have a brake controller, if so check that it is not feeding back to the brake switch.

 

turn/hazard was one of the first things replaced
have had just about every one of my other vehicles screw up at the same time
now I have most of them back on the road can get back to the F-350

next plan of attack on the 86 6.9
cross reference current wiring with the Haynes manual diagram
vs the 87 6.9 wiring

theory is when the PO changed the tilt column with cruise to non tilt/non cruise column
wiring didn't match up causing the current problem

may just swap out the steering column from the 87 to the 86 and trace down all wires
to make sure everything is connected properly

 

I wonder what the problem/solution was for the op brake lights staying on? I got the same exact issue.

 

This thread is 13 years old, and the OP hasn't been on the site for nearly as long. Start your own thread describing your issue and what you've done to try and fix it. Someone will be able to help you.

Closing this thread.