Hand brake warning light and boot light

[alfheim]

Hi

I have a couple of questions I was hoping someone could help we with. 

1. The hand break warning light in my P5b saloon isn't working and I'm assuming it's just the bulb. The service manual isn't very helpful here, and it's almost impossible to get to/see anything under the lamp due to the parcel shelf. From what I can tell there are 4 screws, but not quite sure what they are holding in, and worried that much more than I expect would come loose and be impossible to re-attach if I undo them "blind". Can anyone give a little bit of guidance on how to change the bulb in the hand break warning light. 

2. My boot light isn't working. the bulb works but I get no power to the socket. From what I can tell there is supposed to be a mercury switch here that triggers the light when the boot opens, but I can't see anything. Can someone shed some light (almost literally) on the position and look of this switch? 

Any help much appreciated.

[richardlamsdale]

Hi, from memory I think the bulb holder just pulls-out from the back of the orange handbrake warning light - its just a push-fit. No need to remove any screws.

Regarding the bootlight, yes there's a mercury switch built-in to the bulb holder inside the boot. It was a standard Lucas item. Over time the mercury and/or contacts become dirty, so the switch doesn't work. It could also be the mercury has leaked out. Its just about possible to open-up the bulb holder, then inside there's a plastic capsule with contacts that holds the mercury. I've read that some people have removed the mercury and cleaned it, but personally I don't want to mess with mercury.

The alternative is to remove the mercury capsule, make a spacer that has a permanent contact, then wire the bulb into the sidelight circuit, but that's quite a lot of work. Or just buy a torch  .

Occasionally the boot switches do come-up on eBay - I've seen a NOS one, but there's no guarantee that age hasn't affected these either.

[djm16]

The boot light in my cars will only function if the sidelights are on too.

I have replaced the mercury tilt switch with a mechanical tilt switch (essentially 3 ball bearings in a cage).
Look on eBay for "tilt switch ball".


I also replaced the filament bulb with a LED bulb as the current carrying capacity of the tilt switch would be marginal with a filament bulb.

[alfheim]

Thanks for that. Yup it just pulled out. Just didn't think about that initially.
Unfortunately the bulb was OK. So now on the the next level of investigation. There is no light, either when the handbrake is on or when pushing down on the float on the brake fluid reservoir. Haven't staarted measuring accross the float switch or tried to look for the switch on the handbrake yet, but interested to hear if there are any usual places I should start. 

I'm aware that the ignition has to be on. from the wiring diagram, I can't see any fuses or other switches etc. 


Thanks for the explanation and tip on the boot light. 

Agree a flashlight, sorry torch, is probably cheaper, but it's fun when it works. Yes, am aware that the sidelights must be on, so not quite sure how usefull this is, but hey. 

Anyways will look for alternative switches. 


Thanks 

[alfheim]

When replacing the tilt switch, did you then just  get a new bulb holder?  
If so, any suggestions on where, if not, how do you bypass the switch in the original holder. 


richardlamsdale You said the original holder is just barely possible to open, any tricks on how to do that? Just brute force? heat? twisting?

Any suggestions welcome. 

I bought some new tilt switches, so I was thinking I'd try to replace the original, but then I either need to replace the bulb holder or open it to replace the tilt switch. 

Thanks

[Phil Nottingham]

To dismantle the bulbholder its just a tight twist fit. I have done several. The mercury capsule can be removed or opened up for cleaning the contacts and mercury (its poisonous so at your own risk)

[richardlamsdale]

I couldn't open mine with force without starting to crush the holder, so I used a small hacksaw to partially cut the part that the bulb bayonets into, where it folds-over the main body. This relieved its grip enough to pull-off the bayonet part.

[alfheim]

Thought I'd just follow up on this. 
Managed to open the boot light with no problems, and the mercury switch seemed to be completely gone when measuring, even though I actually had gotten it to work by tapping on it before opening. 
Anyways, decided to go down the route of replacing the mercury switch and had ordered a pack of 10 for 4 USD or thereabouts from e-bay. 
ended up putting the new switch on the outside of the housing and drilling a small hole to feed in two leads to bypass the old switch. Holding the new switch in place with hot glue. Doesn't look fantastic but works. 


This is what the holder looks like taken apart if anyone wonders. The mercury switch is the plastic thing on the top right. 


This is my solution with the new mercury switch hot glued to the side. Simply soldered a short lead to the top and bottom of the old switch, fed them through the hole I drilled and soldered to the new switch. 

Now, moving on to the handbrake/brake warning light. Any ideas there? I have +12 at the light bulb, and by earthing the bulb it lights up. I've also measured the switch on the fluid reservoir and that seems to work, but not sure where the handbrake switch actually is or if there are any good ways to measure the cabling/ grounding of the switches. 

[Phil Nottingham]

The handbrake switch is under the dash at the side of the pull bar at the handle end. They are good switches and rarely give trouble unless they have gotten wet (from a leaking screen seal)

The fluid level switch is a primitive cork float on a needle with brass contacts in the cap which corrode from water diluted brake fluid.  They are not to be relied on for safety as not fail safe

[Brendan69]

It seems its my turn for electrical gremlins this month. LOL.

Firstly I never apply my parking brake on my P5B when she is in the garage.

Fired my car up today with parking brake OFF and immediately noticed the parking brake light was ON which was strange I thought. I wiggled the lever, nothing. Applied it on and then off, It stayed on still. Pressed the brake pedal and it went off but came back on again.

Fiddled with the pedal switch a little and the light was flickering and jiggled the brake pedal a tad and the light went out. Applied the parking brake and the light came on as it should do. Released the parking brake and the light stayed on again. Ive pressed the switch toggle in and out with my finger and no change.

Could it be the brake pedal switch has had it or the parking brake lever switch had it??? all fluids are fine, no leaks and I have a brand new reservoir on the car done by previous owner at his garage he used. Its annoying but its telling me its a simply fix as there are no issues with the brakes.

Ive been JRW and their brake pedal switch looks nowt like the original fitted to my P5B, I guess its a more modern version of the OEM item and it does have the 2 x terminals fitted albeit I cannot see any markings on it as to which wire goes on which terminal or does it not matter??

Thoughts appreciated before I buy them.

Cheers 

[Phil Nottingham]

None of the brake switches are polarity concious.

The brake light switch on the pedal is not connected to the other 2 except via the ignition feed. 

The pressing of the pedal however affects the fluid level which is part of the handbrake light circuit.  The fluid level switch is very primitive just a cork on a needle bridging 2 brass contacts in the cap. These corrode/tarnish/short.

I would never rely on the level light so just keep an eye on the level to see if its loosing fluid.

The foot brake switch is a cheap universal one used on many cars from the early 70s including P5Bs and Land Rovers. They are not long lasting.

[Brendan69]

Cheers Phil, ive ordered a new Lucas brake pedal switch from Gordon of Rover part London and will see what happens once changed.

Regards,

[richardlamsdale]

It sounds like its the fluid level contacts in the reservoir to me. Not sure what fluid reservoir you have, but mine is all plastic. As Phil says the fluid level switch is a cork float on a rod and a brass 'washer' that bridges two contacts when the float sinks. The cork can lose its buoyancy and then the contacts will close, causing the handrake light to come on (by design - its meant to warn of low brake fluid).

I removed the reservoir cap, pulled-off the aluminium tube that the float sits in, and the float is inside. I made a new float from cutting-down a wine bottle cork. If you want to give it all a clean, you can also prise-out the centre of the cap (the bit with the two contacts that the wiring harness attaches to) and get to the contacts, but mine was very tight to prise-out.

[Brendan69]

Hi Richard, An oversight on my part and yes indeed you were correct. My fluid level was ever so slightly low albeit didn't look low but ive topped up and all is well now so cheers.

Another £15 wasted on a new switch but it will be added to my box of spares I hold as you never know. Yes mine too is the newer type all plastic reservoir and its only in the last 12 months been fitted by the last owners garage he used by looks of it as its brand-new looking so just to be sure ive taken a good long look at everything and there are no signs of leakage or weeps anywhere so for now im happy again.

Still getting used to being back in the old skool car ownership game but its all slowly coming back to me over time.

Cheers again