No brake lights, 3rd brake light glows constantly

[bryansr]

I came home last night to find the 3rd brake light on my parked 98EB with a dim glow. Hit the brakes and found the brake lights do not work but the 3rd BL did. I'd had the battery disconnected earlier in the day, and did so again last night to avoid draining the battery.

Getting ready to tear into it today. Any thoughts on what to look for? Thanks, Bryan

 

[J_C]

First guess would be that your brake pedal switch has failed to a partial (barely conductive) shorted state, that's passing current to all the lights but at so little voltage that only the 3rd light can make visible light due to being LED.

Try the hazard light switch and see if the brake lights come on with that. If so, everything after the junction between those two points should be good.

When you had the battery disconnected earlier in the day was it for this reason or was it for some other reason then the brake lights only started acting up after the battery was reconnected? The latter wouldn't really make sense on a '98 (could be coincidence) but I thought I'd ask.

 

[bryansr]

I'd had the battery disconnected to replace the radiator. Yeah, not really necessary, but that's what my manual said to do.....

 

[J_C]

Disconnecting the battery to swap the radiator could be a good idea. I vaguely recall reading somewhere that used coolant can be electrically conductive, though I wouldn't expect it to conduct much and it's nowhere near any circuits I can think of that would be that sensitive to a low conduction rate.

I added a wiring diagram attachment to my prior post.

 

[bryansr]

I'm not sure what's normal, but only the amber rear lights blink with the hazard flasher switch on. Should the red brake lights also flash?

 

[XLTrunner]

Just the amber lights.

 

[J_C]

Heh, I didn't remember which hazard lights come on either!

According to the wiring diagram you can unplug the connector to the brake pedal switch and short the #5 light-green/red to the #4 light-green at which point the brake lights should come on if it's the switch, and when you unplug the switch, before shorting those two wires, the 3rd brake light would go out, though I don't know how easy it is to see dim LEDs on a sunny day.

Ultimately you can use a multimeter to see where there's power when there shouldn't be, and where there isn't when there should be once the pedal is depressed, or if shorting the two wires together doesn't cause the lights to come on.

 

[bryansr]

I'm a littel embarassed to say this, but it turned out being two bad bulbs. Replaced them both and the signals work normally.
With the 3rd brake light constantly glowing and neither side's brake light working, I thought it was something major. Since both bulbs went out at the same time, maybe there is.....

Thanks to all

 

[J_C]

Both L & R bulbs out shouldn't cause the 3rd brake light to be dimly lit.

It's good that you have brake lights again, but IMO there is something still going on. I'd keep an eye on battery voltage to be sure it isn't drained too low.

 

[koda2000]

I'm confused. The signals and brake lights are not the same bulbs or circuit and, as said, bad bulbs would not cause the 3rd brake light to stay on. You have something else going on. My guess would be a bad brake light switch.

If you did have 2 bad brake light bulbs (nothing to do with the rear signal bulbs) and if you've replaced them now and everything seems to working normally I suspect you will be experiencing all your brake lights will now stay on at some point due to a bad brake pedal switch. Having disconnected your battery while replacing your radiator should have nothing to do with anything.

 

[bryansr]

I misstated, I meant both brake lights were working after the bulbs were replaced, and the 3rd brake light is no longer glowing dimly when everything is shut down.

 

[koda2000]

I misstated, I meant both brake lights were working after the bulbs were replaced, and the 3rd brake light is no longer glowing dimly when everything is shut down.

Okay, but that still does not explain why the 3rd brake light was glowing dimly. It doesn't get any power unless you depress the brake pedal.

 

[J_C]

^ Agreed. I'd pull fuse 13 (or whichever his has for brakes) in the interior fuse panel and use a multimeter to measure current there, when the brake pedal is not pressed there should be none.

A flaky switch that keeps cycling the lights on can also cause the bulbs to burn out prematurely, though it's hard to call 22 years prematurely if they're the factory bulbs.

Then again if the switch is flaky it could further wear the contacts and no longer have a low leak state, but it could also mean the switch is that much further towards end of life. Considering how important it is that brake lights work, I'd just replace it. They're only ~$15 (Motorcraft) or less (3rd party brands) on Rock Auto and Amazon.

 

[koda2000]

^ Agreed. I'd pull fuse 13 (or whichever his has for brakes) in the interior fuse panel and use a multimeter to measure current there, when the brake pedal is not pressed there should be none.

A flaky switch that keeps cycling the lights on can also cause the bulbs to burn out prematurely, though it's hard to call 22 years prematurely if they're the factory bulbs.

Then again if the switch is flaky it could further wear the contacts and no longer have a low leak state, but it could also mean the switch is that much further towards end of life. Considering how important it is that brake lights work, I'd just replace it. They're only ~$15 (Motorcraft) or less (3rd party brands) on Rock Auto and Amazon.

Make sure you buy the right brake switch. There's one for cruise control and one w/out CC. The manual trans might also use a diff switch too, but I don't think so.

 

[blduke]

Make sure you buy the right brake switch. There's one for cruise control and one w/out CC. The manual trans might also use a diff switch too, but I don't think so.

I came home last night to find the 3rd brake light on my parked 98EB with a dim glow. Hit the brakes and found the brake lights do not work but the 3rd BL did. I'd had the battery disconnected earlier in the day, and did so again last night to avoid draining the battery.

Getting ready to tear into it today. Any thoughts on what to look for? Thanks, Bryan

I know this gonna sound strange but see if the lights go on or off with your tilt wheel all the way up. My 2001 had a green wire pulling out of the combination switch on the steering column. I took the steering column cover off and pushed the wire in and my brake lights started working again. This is a common problem, and I found the solution here on the explorer forum. I guess the brake lights route through the steering column but the third eye doesn’t.

 

[ibstang]

Another consideration...Pedal return springs can lose some of their vigor over the years, allowing intermit gremlins to pop-up. Also, it might be worthwhile to check for solid ground from the lamp-holder plugs to chassis. I've seen all sorts of bizzaro symptoms where stray current tries to find its way around partially resistive grounds...Good luck...

 

[koda2000]

Another consideration...Pedal return springs can lose some of their vigor over the years, allowing intermit gremlins to pop-up. Also, it might be worthwhile to check for solid ground from the lamp-holder plugs to chassis. I've seen all sorts of bizzaro symptoms where stray current tries to find its way around partially resistive grounds...Good luck...

Agree that bad grounds can cause all sorts of strange problems that seem inexplicable.

 

[mic98xlt]

Years ago I had the same odd 3rd brake light flicker as OP describes with no brake lights. I too have a '98 Explorer XLT with the LED type 3rd brake light. I then began to over analyzed what could be wrong for days. It was just that both rear brake lights bulbs burnt out at almost the same time. With both rear brake light bulbs being "open" it somehow allowed stray voltage to appear at the 3rd brake light. That was why with no normal brake light bulb resistance (open circuit) the 3rd brake light flickers on dimly. I replaced both rear brake light bulbs and never had a problem again. Strange but true.

 

[koda2000]

Years ago I had the same odd 3rd brake light flicker as OP describes with no brake lights. I too have a '98 Explorer XLT with the LED type 3rd brake light. I then began to over analyzed what could be wrong for days. It was just that both rear brake lights bulbs burnt out at almost the same time. With both rear brake light bulbs being "open" it somehow allowed stray voltage to appear at the 3rd brake light. That was why with no normal brake light bulb resistance (open circuit) the 3rd brake light flickers on dimly. I replaced both rear brake light bulbs and never had a problem again. Strange but true.

Hugh, good to know.

 

[harrison.m.k]

Years ago I had the same odd 3rd brake light flicker as OP describes with no brake lights. I too have a '98 Explorer XLT with the LED type 3rd brake light. I then began to over analyzed what could be wrong for days. It was just that both rear brake lights bulbs burnt out at almost the same time. With both rear brake light bulbs being "open" it somehow allowed stray voltage to appear at the 3rd brake light. That was why with no normal brake light bulb resistance (open circuit) the 3rd brake light flickers on dimly. I replaced both rear brake light bulbs and never had a problem again. Strange but true.

2 years late but I just read on another forum that stray voltage could be caused by the alarm system. This is also what can cause both main brake lights to go out at the same time. The post said cutting the wire from the alarm system leading into the brake lights is an easy fix instead of replacing the whole alarm relay.