Discovery 2 Electrical: Brake Lights Issue

[Gnasher_PNW]

Good day, fellow Overlanders.

Hoping there are some senior Land Rover enthusiasts around to help me out.

I've run into an issue that has me perplexed, and I believe I may have it narrowed down.

Today, I found that I couldn't shift out of park (I drive a 2003 Discovery II), and thought to myself "shit, my brake switch is at it again".

I check Fuse-25 in the drivers fuse box and low and behold it has blown (15a).

I replace it, and then inspect my brake switch, to ensure that I don't need to reset it. It looks fine, so, I try shifting again. I'm able to shift and head off to work.

I found out later that my brake lights are out the entire drive. Well, my running lights for the LH light housing work, as do all my signal indicators, it's just the RH running light that doesn't, and then both brake lights don't activate.

I've spent a little bit here at the hangar trying to trouble shoot.

Fuse-25 blows constantly.

Fuses 11, 14, 29, and 33 are intact.

Inspected RH lights, none are blown.

The brake light isn't receiving power (I left the blown fuse sit unchanged, i expected this)

Changed the brake light out with a new 1157 bulb, and in noticing a bad fit for the turn signal light, I change that too. I then turn on the RH signal indicator for the hell of it. It signals just fine, but is now flashing my tow light... Weird.

I figure the 1157 might be too much for it and change it back to its original, no issues.

I checked for voltage in the driver side fuse box with Fuse-25 out, receiving 12V+, good.

With the brake switch disconnected, I check the Green and Orange wire that sits on its 3rd pin, straight from Fuse-25, 12V+, good.

Reinstall brake switch with new fuse, it blows the fuse....

Since I had the brake switch disconnected, it would believe the brakes are applied and try to signal the lights.

Knowing that the switch, fuse box, are acting correctly, is it safe to assume that I've got a bad wire somewhere in the rear of the vehicle?

Grounds appear okay, and I've yet to track down the trailer harness to give it s good look over.

At a loss otherwise, and it has me legally/morally stranded at the squadrons hangar, ha.

If anyone has some insight, I'd be most appreciative. Last thing I need to do is keep feeding it fuses, I'll burn out my harnesses.

Thanks in advance!

-Ryan



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[RiverCityDave]

I went through an issue with these exact symptoms, and I am 99% sure it was a ground issue. It's been several years, so let me find my notes and see if they have any info.


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[Gnasher_PNW]

You're the best, again, Dave. Thank you.

An odd note, whenever I "sort" the issue out and do get the brake lights to work again, only the LH running lights will come on. When I put the transmission into Park, is when Fuse-25 will blow, and then I can't shift out of Park again.

Quite odd. If it's simply a grounding issue, awesome.

Thanks for replying, I really appreciate it.

 

[RiverCityDave]

Ok, so my notes say it was frayed wiring adjacent to the left rear tail light, but I found that by tracing up from the trailer wiring harness, there were several sections that had been coated by mud and funk and were shorting against the inner structure of the quarter panel. It was definite,y causing the symptoms you're having.


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[Gnasher_PNW]

Interesting.

I take it I'll have to take off the quarter panel to get to all of that? There honestly doesn't appear to be a lot of room to get to the upper section of that harness, above the trailer hookup.

The trailer harness didn't look too bad, when I inspected it earlier. I will give it another look, and see what surprises might be in store.

I'm hoping it's just that.

 

[Gnasher_PNW]

Tore everything apart, found nothing amiss with the trailer harness plug in. Nor did I find anything concerning with the wiring bundles inside the LH/RH bulb housings, or the wiring on the outside leading to them.

Now, I did manage to get the RH running lights to come back, needed a new fuse, easy win.

So, I changed fuse 25 again, and I pressed the brake pedal around 5 times, the brake lights came on each time, I could hear the shifter solenoid disengage each time, and then on the sixth push, the fuse blew.

Forgot that I had at one point taken the brake switch off its bracket, and replaced the fuse. Epic flash and the fuse was toast. My bad...

I am beginning to wonder if I should just get a new brake switch?

 

[RiverCityDave]

I have the factory service manual, I wonder if there is a procedure for testing it? I'll dig into it and look. Wait one.


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[Gnasher_PNW]

I imagine there is a huge difference between that and that RAVE manual? If so, I need to find myself in possession of one.

Thank you.

 

[RiverCityDave]

Have you tried jumping the wires and bypassing the switch altogether? Jump the green/purple wire and the green/orange wire; the brake lights should come on, the system is looking for continuity. I mean all this would do is prove your switch is bad.


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[Gnasher_PNW]

I have not done that.

I will give it a try.

If the fuse still blows, then that means I'm going to be wire hunting...

 

[RiverCityDave]

Yeah that's exactly my thinking as well. Even the FSM suggests flexing the wires and moving things around to try to replicate an intermittent fault.


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[Gnasher_PNW]

I'll need to try that in the morning, as it's about time to hit the rack.

Thanks again for you help, Dave.

I'll post again tomorrow with progress.

 

[Gnasher_PNW]

Okay, I jumped those wires with the brake switch disconnected, and the fuse blew immediately.

I think there's a short towards the fuse box(?).


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[Gnasher_PNW]

The wiring underneath the dash looks clean, though.

I suppose regardless of that fact, I'll just have to take it apart anyways and see what may be hidden.

I'll return to the rear of the vehicle for another look as well.

I got all lights back there working last night.

After work it will have to get done, along with staying up late to prepare for my house turn in inspection tomorrow... I have duty tomorrow, hopefully I fix this issue.




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[Gnasher_PNW]

No luck at all.

I could find nothing wrong with the wiring at the fuse box and towards the switch.

I have found nothing wrong with the grounds in the rear of the vehicle, except for in the LH light housing. It appeared to have a lot of resistance on the power coupler that connect to the housing itself.

What else is odd, is that my running lights will work, but when the brakes are applied, the fuse blows as the lights only increase in brightness by a tiny amount. Turning the running lights off (which are very bright) and then hitting the brakes shows that the lights are now extremely dim.

I had taken out my reverse lights to put into my LH RH housings, but have since installed completely new lights for all housings, except for the reverse lights. Putting a single light into the LH reverse light housing did nothing but blow the fuse, yet the light would come on.

I'm at a loss. Trying not to lose my patience, but I am literally four days away from checking out of leave and needing to have everything moved out of my house. I am stressing super hard.

Not to mention I still have work the next few days, and I have 24 hour duty posts.... all of which will require me to catch a ride from someone. Really awesome timing for all of this.

Anyways..... I am considering ordering new tail light housings, maybe a new brake switch?

It sucks so bad, I had it fixed too! I replaced all of the lights and had literally no issues all damn day!

 

[Gnasher_PNW]

Honestly, I probably can't even order most of this stuff in anyways, seeings as I have to turn my house over on the 11th and won't have anywhere to send anything, except for the place we're trying to go on leave.

...

 

[Gnasher_PNW]

Going to tear apart my center console tonight.

I've found all of the earth header locations.

It appears that fuse 25 branches out to two different paths.

A. Red/Blue wire to the Solenoid Interlock Transmission and Diode G126.

B. Green/Orange wire to the brake pedal switch, then to header 0287 via a Green/Purple wire into the Body Control unit, going to a shared earth with the Sensor Neutral Transmission T193.

The shares ground is: Earth Header 0552 in the center console, passenger side.

Fingers crossed.


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[Gnasher_PNW]

Took apart my center console, got to C0552 and cleaned it up, reinstalled and then made sure all of the bullet connectors were seated tightly.

Golden for a few hours.

Get to storage unit, shut down, stuck in park haha.

So, after a harrowing three hours, I take apart the rear earth headers and rebuild them, re-seat the bullet connectors, re-fuse the fuse box and get on our way, no issues.

Same fuse this morning is in fuse-25, and I have charged the battery. Now at 14.4V, not the 12.78V the charger found it at....

Scrubbed every ground in the engine bay once more, and go to my duty post. No issues, surprisingly. (I made periodic stops to put the vehicle into park, and see if the shift solenoid would disengage when I hit the brake pedal, and it would).

So far, It's holding up... but I cannot find my confidence for it.

Going to di-electric grease all of those earth headers.

 

[Gnasher_PNW]

Should have updated awhile ago.

All of that wire tracing lead me nowhere. Everything was as it needed to be.

Brake lights went out again on a trip to the grocery store, pulled the running light fuses (11,33) and replaced them with brand new fuses, everything worked.

Then they stop working again while my wife and I are at the storage unit. I zip tied all of the wire bundle away from the engine bay as much as I can, no problems ever since.

It was heat that was causing my issues.

 

[RiverCityDave]

Dude you're kidding! I'm stoked that you solved it, but what a weird issue for a Disco, I thought I had every problem you could have with one.


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