Brake Light Switch Replacement |
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Stop Light Lamp Circuit pdf2460 viewsThis pdf shows the brake light circuit for the NAS LR3.
Note that power for the brake light bulbs can come either thru the brake light switch power feed /contacts plus also from the Hill Decent Control, (HDC), system relay located within the Central Junction Box, (CJB) - yes two separate sources of power for the brake light bulbs. This would tend to explain how a brake light circuit concern shows up as a hill decent fault message; also why lesser vehicles without hill decent braking mechanisms, (HDC), never display this sort problem when a brake light bulb or switch acts up. You never have a problem related to a system that does not exist.
Additional evidence of the relationship of the HDC and the tail light circuit is demonstrated by when the HDC actually acts to slow the 3 down, the brake lights automatically illuminate even if the slowing action was merely retarding the engine speed or shifting to a lower gear, (in other words, no foot on the brake pedal).
There is also a tie in to the Cruise Control and hence a failing brake light switch can affect cruise operation or just create false Cruise Control messages. To further complicate the issue, while there are no messages generated, operation of the radiator electro viscous fan can also be negatively affected by the fouled set of secondary contacts within the brake light switch. This is all because the NC contacts within the brake switch send misleading messages to the ECU.
While the ground wire design is similar to other vehicles, note the grounds for the brake light filament and the reverse light filament are common on each side. That means that if one has a non functioning brake light on one side, the reverse light may not also work or that some problem with the reverse lights could back feed into the brake lights. This situation while unusual, can result when grounds are corroded probably due to swimming in rivers and creeks or just routine driving in a marine environment.
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LR3 Brake Wear Sensor Wiring1488 viewsThis 1 page wiring diagram pdf shows that both the front and rear brake pad wear sensors are part of a closed series circuit to ground.
In operation, when all is good, the series circuit is grounded and the amber brake wear warning indicator on the instrument panel is not illuminated.
When the pads on one wheel, either the left front, or right rear, become too worn, the respective sensor is "cut" which results in an open circuit condition. This causes the dash brake wear indicator to illuminate.
The circuit is like the old style Christmas light strings where one burned out bulb caused the whole string to go out.
A quick field fix to get the dash light to extinguish in lieu of replacing the sensor and pads etc is to disconnect the brake pad wear sensor and short across the two open conductors of the vehicle side connector plug. This of course means you now have a normal vehicle, one of the thousands that do not feature brake pad wear information systems.
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Land Rover Brake Light switch XKB5001102675 viewsThis is what the switch looks like when removed from the parts box. Note that the plunger is recessed back into the body and when installing, the process of rotating the switch body 1/4 turn anticlockwise releases the plunger so it pops longer and engages the brake pedal. If you look down on the plunger you can see curved slots where the rotation takes place.
Do not try to rotate the new one - play with the one you remove. Also do not press on the brake pedal when removing or installing as you will damage the plunger - this is one of the reasons the plunger is retracted into the body for installation. It is also for this reason that if you try to confirm the operation of the switch contacts with an ohm meter by pressing the plunger, the switch will appear not to function as one might anticipate. Have faith, the switch will however, once installed and the plunger is in full motion.
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Switch is blue colour thing thru the rectangular opening.3149 viewsThe blue coloured plastic bit thru the rectangular opening is the brake light switch. The fist time, I found it easier remove the switch by dropping the horizontal plastic panel, (two screws), and then slipping my hand in and rotating the switch clockwise 1/4 turn. The second time, I was able to remove the switch thru the rectangular opening and did not need to remove the horizontal lower panel. Obviously, I had to remove the sloping knee pad panel, (note sort of hinged at the bottom so pull back from the top.)
Regardless, do not touch the brake pedal - just let it sit where it wants to. One has to first remove the angled knee pad panel that sits under the steering wheel. It can be pulled from the top corner at the door side. Pulling releases a pair of those U shaped metal clips that LR loves so dearly. You have to pull quite hard. The bottom is held by a couple of plastic fingers in a couple of slots so you pull at the top till the two clips release and then rotate the panel and pull upwards a bit.
To remove the switch, you rotate it clockwise and pull outwards. Rotating the switch clockwise automatically retracts the plunger back into the switch body away from the brake pedal arm.
Similarly when you install the new switch, the required 1/4 turn anti clockwise rotation action releases the plunger so it lays up against the brake pedal arm and at the same time, secures the switch in place.
To remove the electrical wires, the switch will drop below the horizontal pad and hang from the wires so unclipping the electrical connector plug is fairly easy to do.
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Black Deposits on Brake Light Switch Plunger2730 viewsThis jpg I got off another forum and is typical of what one will see when one opens up the removed brake light switch. The black powder is residue from arcing of one of the pair of contacts within.
Hopefully the newer switches with the FOMOCO logo moulded into the plastic are improved from the Land Rover logo marked early units, however I doubt it.
The Ford part number is SW-6572 and/or 7E5Z-13480-A as used on the 2006 to 2009 Ford Fusion's and Mercury Milan's; the Land Rover part number is XKB500110. Cost of switch could be about twenty five dollars. A previous LR part number for the switch was XKB500030, so hopefully the newer LR part number, XKB500110, reflects some improvement in reliability.
It is possible that the new switches are better as I installed a replacement 72,000 km, (45,000 miles) later, at 195,000 km (121,000 miles). When I took the removed switch apart to inspect, it was clean inside. There was no black dust - the switch looked like new, hence they must be improved now.
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Brake Switch Visible thru Opening4933 viewsThe blue and white bit is the switch; the sort of gold appearing box,(it is really black), you will not see in your 3 as it is a Smooth Talker brand amplifier for my Blackberry phone antenna. This install is detailed in the SmoothTalker phone antenna section of my gallery.
One way to remove and install the switch is to lower the "horizontal" panel above the brake pedal as shown where the flashlight head is located. To actually remove the switch, you slide your hand thru the gap and rotate the switch clockwise 1/4 turn while watching thru the rectangular opening. Installation of the new switch is the reverse of above - 1/4 turn counterclockwise.
Before you remove the switch, note its orientation - horizontal with electrical wires to the left. That is the way it should look after replacement as well.
The second time I replaced the switch, I did it all thru the rectangular opening and did not remove the horizontal panel - that is experience helping out.
The knee kick you have to remove regardless. It is sort of hinged at the bottom so you just pull at the top and sort of rotate the knee panel and then pull upwards for two plastic "fingers" to clear the slots they reside in.
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Brake Light Switch, Find, Remove, and Install Instructions 7775 viewsThis is a two page doc outlining where to find the brake light switch, how to remove it, and then install the new one.
Note, do not move the brake pedal when removing or installing the switch. Let the brake pedal hang where it wants to. The switch design is actually cunning, and as such is supposed to make the removal and install fool proof. Hence if you think too much about it, you can wreck the new switch.
If you want to inspect the interior of the switch, wait until you have removed the old switch. You can then just unsnap the blue from the white to get it apart. Inside, the switch is quite simple, (no circuit boards), but it will probably show black dust from failing contacts.
I think the reason the switch fails is that the Normally Open, (NO), contacts of the brake light contacts were made too light to carry the current load for make and break of the tail light filaments. I also think the black dust created then fouls the Normally Closed, (NC), second set of contacts for the ABS circuit. As such, the Normally Closed contacts become intermittent in operation and display as a fluctuating open and closed circuit condition to the ABS system when the ABS should be seeing a steady closed circuit. Hopefully the replacement switch contacts are more robust and may be as I recently replaced my switch again just as a matter of maintenance. While in a redesign, ideally the NC contacts should be sealed or at least separated from the NO contacts, when I inspected the removed switch, this time there was no black dust present.
Probably the removed switch will have a Land Rover oval logo moulded into it, the new one, FOMOCO.
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Black Deposits to interior of Brake Light Switch2830 viewsThere are two contacts, one on each side of the vertical plunger under the copper metal. The set of normally open contacts on the left side that carries the power for the brake light filaments, (15 amp fuse F15P), is apparently not heavy enough as the contacts deteriorate and generate the black residue.
The set of normally closed contacts on the other side appear to be sized OK. There is not as much current, (5 amp fuse F66P), flowing thru the contacts to the ABS module, however the contacts are likely adversely affected by the black residue produced by the other deteriorating set of contacts.
One presumes/hopes that the newer replacement switch now has contacts heavy enough to carry the brake light power. It would be ideal if the ABS set of contacts were sealed from the brake light contacts to prevent contamination of the normally closed set of contacts.
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Brakes Description and Operation2200 viewsThis is a 17 page pdf that describes the operation of the various braking systems: the ABS, CBC, DSC, EBD, ETC, EBA, EDC, and HDC. Also discussed is the yaw rate and lateral acceleration sensor as well as the steering angle sensor.
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Land Rover Stop Tail Light dual filament bulb nominal 12 volt 21 / 5 watt filaments1412 viewsThis is the Land Rover part number 264590 dual filament bulb, (P21/5), that inserts into the upper two tail lamp receptacles. In the upper one, both filaments function, in the lower one, only the 5 watt tail light filament functions.
I regard it as not a good practice to routinely switch bulbs when the tail light filament, (5 watt), burns out on the lower bulb. The broken filament can jiggle over onto the brake light filament, (21 watt), and short the circuit to ground or something else not predicable.
There are also arguments to say that quality control is better on the Land Rover marketed bulbs than say far east sourced bulbs. Filament construction, and hence resistance can vary and mislead the current sensing circuits monitoring the signal light systems. Also when the bulbs are properly installed, all filaments should be standing vertically and not at any slope.
These are the sort of obscure circumstances that can lead to false trouble messages on the display, dropping to the stops, and subsequent concerns - all over a tail/signal light bulb.
For example, the filament life of both the tail light and the brake light filaments in the P21/5 bulb is significantly less than the USA common 1157 dual filament bulb, (1000/250 vs 5000/1200 hours); brightness in the P21/5 is a bit more, (3cp/35cp vs 3cp/32cp where cp is candle power), but current consumption is oddly less, (0.44a/1.86a vs 0.59a/2.10a where a is amps). It is the quest for efficiency vs maintenance trade off.
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