How to repair a faulty parking brake light circuit in a 2000 Ford F150

    A smoking right rear wheel was the first hint that the parking brake switch had failed on my 2000 ford F150. I had set the brake when hooking up a a travel trailer. There was no “Brake On” light to remind me that it was still on as we took off on an eighty mile drive to a campground.  The right rear wheel was  stinking and smoking as we registered for the campsite.  Only then did I realize that the brake had been on, albeit lightly, for the whole distance.  This little spring- loaded switch may not seem like much, but it simply has to work. When I got back home I went to work on replacing it. It’s in there pretty deep and is not easy to get out. There is a 7mm hex head screw holding this little white plastic switch but I could find no way to reach it without tearing stuff apart…

1) To improve the view, remove the threshold plastic cover and the left side front cover. Both pieces simply unsnap with a good stout pull. Remove the threshold first.

Remove the side molding after taking off the door threshold molding

2) Unbolt the three 10mm bolts holding down the parking brake mechanism. There is one an upper , a lower and a front bolt. The front is hardest because of limited access and a very short turn radius for the 10 mm open end wrench that is about all that will fit in there. I found it helpful to remove a wiring harness panel fastener to allow the harness to be position out of the way. The other two are fairly easy to remove with a six inch extension bar on 3/8’ ratchet. The upper has to be engaged by feel, though, as it’s up and back in there a bit.

Unbolting the lower 10mm brake assembly mounting bolt

3) Unplug the wiring connector going to the switch. This took a squeezing motion on the opposite sides of the plug with a finger from each hand.

4) Pull the parking brake mechanism downward. This requires some pretty serious jostling and pulling. When it gets low enough to reach the 7mm screw head mounting the switch, remove it with a nut driver.

The 7mm switch mounting screw is now reachable with a nut driver

5) The switch is simple and all the working parts can be seen. The spring loaded plunger has a floating washer on one end that makes contact with two strips of metal. One goes to the electrical stab-type tab for the wiring plug and the other to the ground connection provided by the 7 mm screw. In the brake applied position the plunger is out and the washer touches both contacts. The switch closes and the brake light comes on. For it to malfunction in this position the circuit must be open somewhere. When tested out of the truck with an ohmmeter the switch works perfectly every time. There is a problem with the ground connection or the wiring connection or the wire.

An ohm meter test proved the switch to be good,. Brake off position shown

Repairing the connections

     I decided to improve all connections and contact surfaces in order to fix the problem

1) Clean all contact surfaces of the switch with contact cleaner.

2) Add a lock washer to the switch hold down screw. This will do two things. It will improve the ground connection and also keep the screw from working loose.

The addition of a serrated lock wash will fix the likely cause: a poor chassis ground. 

3) Test the repair in the vehicle. Do this before fully finishing all installation work in case there is still a problem. It is necessary to mount the switch first, then move the parking brake assembly back into position and plug in the wiring connector. Securely bolt down one of the mechanism mounting bolts. The lowest one is the easiest. It tested fine.

Installation

1) Finish mounting the parking brake mechanism. (two more 10mm bolts)

2) Snap the side cover back in place. Note the plastic projection on a wiring mount that fits into a slot in the back of the cover.

3) Snap the door threshold cover back in place.

4) Do the final test on the operation of the switch. Make sure it works every time!

Here are some links to products useful in this repair:
                                       Professional            
Electrical                        Digital multi-               Economy
Contact cleaner                  meter                    Mulitmeter