third brake light stays on

[big white bufflo]

i have a 2002 winstar only the third brake light stays on after the car is shut off some times all three bulbs some times only the outside two any help is good

[LeSabre97mint]

Do you have trailer wiring?

[danielsatur]

Is there a stuck on Relay for this 3rd break light?

[big white bufflo]

no i dont have trailer wireing and is there a relay just for the third light

[Selectron]

I haven't looked at a Windstar wiring diagram for a while; I'd forgotten just how convoluted the wiring can be for even such a simple function as a brake light.

The third brake light receives 12 volts any time the ignition is switched on, and also for up to 30 minutes after the ignition is switched off, via Switched System Power Relay 3 (relay SSP3) and then fuse 12 (20 amps, central junction box). The brake light has no direct ground connection, but instead whenever the brake pedal is pressed, the Rear Electronic Module (REM) switches the brake light to ground, and the three bulbs within the light assembly will illuminate.

No need to look at relay SSP3 nor the fuse, because they aren't involved in the fault - the problem is on the ground side of the circuit.

The ground connection between the brake light assembly and the REM is via a single wire, so if the REM was erroneously switching the light to ground then all three bulbs should illuminate. Similarly if the wire between light assembly and REM was damaged (intermittent short to ground) then all three bulbs should illuminate. So, because sometimes all three bulbs illuminate but sometimes only the outer two, I reckon that's telling us that the problem is within the light assembly itself - i.e. within the lamp housing, so I'd gain access to that and give it a very close visual inspection, looking for physical damage or corrosion. The ground side of the circuit should be completed by a tan/light blue wire, so that's the side of the circuit that you're interested in.

There is an outside chance that you actually have two faults - a problem within the housing itself causing sometimes only two bulbs to illuminate, sometimes three, and then also an intermittent short to ground on the tan/light blue wire between light assembly and REM. Either way though, you'll need to open up the lamp housing so I'd start with that, and only investigate the wire later if you still need to.

You'll find the wiring diagrams at the Autozone website in the Repair Info section, or these links might take you directly to them:

On diagram 1, you'll see relay SSP3, and immediately below it a triangle marked 'A' - you can pick up that point 'A' at the top right of diagram 2, feeding into fuse 12, and then into the high-mount lamp assembly - everything up to that point is working ok - your fault is either in the assembly itself or the wire which you can see running between lamp assembly and REM.

If those links don't work then try these instead: diagram 1, diagram 2.

[Selectron]

I just remembered - somebody (Northern Piper?) has said several times that a blown bulb in the high mount brake light assembly can lead to a flat battery. Sounds odd but I don't doubt it for a moment because the Windstars do suffer from all sorts of weird, logic-defying electrical faults.

I'd open the lamp assembly, remove the centre bulb (the one which sometimes lights, sometimes doesn't) because it might be faulty, and see if that alone might cure the fault, and if it does then just pick up a replacement next time you're passing a parts store.

[northern piper]

yep, it's true. As much as I can't seem to find a logical or electrical reason for this to happen it has to me and others. The other thing that could be bad is the BOO switch which is attached to the brake pedal. I took mine apart about 8 months ago and repaired it. (couldn't believe that was possible but it was pretty easy). This repair solved the problem, tho just a while ago I did replace it with a new one as I'd ordered it.

[mark_gober]

Just FYI, Here's a picture of how the 3rd brake light is wired on a 2000 Windstar. I'm sure its similar on the 2002, if not identical.

Mark