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Brake light issues
joemotion - 3/1/09 at 11:24 AM

Hi, i am having diffficulty getting the brake lights to work on my newly bought and nearly finished Avon. The problem is i didnt build it and am in the learning process on how to sort things on such a car!!



The previous owner has advised they did work and that i should check the earth etc and have a look at the connections at the front - see pics!

I have had a play and still cant sort? any ideas?

[Edited on 3/1/09 by joemotion] Rescued attachment brake res resized.JPG
Rescued attachment brake res resized.JPG

joemotion - 3/1/09 at 11:25 AM

earth Rescued attachment earth pic amended.JPG
Rescued attachment earth pic amended.JPG

A1 - 3/1/09 at 11:35 AM

all i can say is check all the connections etc, start from the easiest things to check, like bulbs and fuses, and work to the really hard ones...
good luck

joemotion - 3/1/09 at 11:43 AM

if a bulb was out i would assume the other ones would still work? i will have check though and see!! cheers

prawnabie - 3/1/09 at 11:50 AM

There will be a void full of air in that t-piece!

I would unscrew the switch and press the pedal slowly whilst catching any spilt fluid, then screw the switch back in at the same time.

Might not fix your problem but surley the less air in the system the better?

HTH
Shaun

Ian D - 3/1/09 at 12:36 PM

Have you shorted the two wires on the switch. If the brake lights illuminate you will have narrowed down your problem to the switch. If this does not work,I would suggest disconnecting the battery and putting an ohm meter across the brake switch to see what happens to the resistance when you press the brake pedal. If it remains high you may have an airlock as described earlier. Alternatively have you checked the hydraulic switch. I read somewhere that there are different prressure operating switches and this may be the cause your problem.
ian

BenB - 3/1/09 at 01:31 PM

My problem solving method here would be:

Q1) Does the light come on at all when you press the pedal?
A1) Yes, but you have to press really hard = air under switch, bleed as described above.

Q2a) Disconnect the spade terminals from the brake switch. Connect a multimeter across the terminals. Press on the brake pedal. Does the resistance suddenly drop to zero (or near it).
A2a) No = knackered brake switch.

or

Q2b) Get a little bit of wire and stick one end of it down each of the backs of the terminals where it attaches onto the brake switch. Make sure each end of the wire connects to the brass gripper on the appropriate terminal. This will bridge the switch. Do the lights come on?
A2b) Yes = switch knackered.

Q3) With the ignition switched on attach one end of a voltmeter to the battery negative and using the other multimeter probe back-probe the terminal (ie stick it down the back of the terminal until it touches the brass wire gripper). Do this for both terminals. One of the terminals should show 12v. Make sure you remember which if it does. Did it?
A3) No = problem with +ve feed to brake switch. Check fuses.

Q4) With the ignition off and the multimeter on resistance setting connect one probe of the multimeter to the battery negative and back-probe the terminal which was not at 12v in test 3. Does the resistance drop to a fairly low reading (10 ohms or less)?
A4) No = error in negative supply to brake switch.

If the switch is working, you're getting a +ve supply to the switch and a negative supply (through the bulbs) to the switch and it's still not working something v strange is going on

joemotion - 4/1/09 at 10:30 AM

Being as new to this as i am i am assuming when you mean switch its the one with the green wires coming out of it? Dont laugh if it isnt just that i am very new to all this and want to try my best to complete it myself!

Thank you for all your help - just off to get myself a multimeter!

iank - 4/1/09 at 10:59 AM

quote:
Originally posted by joemotion
Being as new to this as i am i am assuming when you mean switch its the one with the green wires coming out of it? Dont laugh if it isnt just that i am very new to all this and want to try my best to complete it myself!

Thank you for all your help - just off to get myself a multimeter!


Yes, its a pressure switch.

First things I'd do are check the fuse isn't blown, then short the switch to see if they come on properly.
If it used to work it's likely to be one of those two.

There are alleged to be two models of switch with different pressure settings, a high pressure switch mounted like that (i.e. with a bubble under it) in the rear circuit wont come on unless you're pretty much doing an emergency stop.

Could be an earth problem, but I wouldn't expect a working system to suddenly develop an earth fault unless it was pretty badly done first time around and/or the car had been left in the damp for a while (from the looks of the wishbone washers it's been kept dry though.

BenB - 4/1/09 at 05:43 PM

Yes, the one with the green wires coming out of it. The two white things on top of the brake master cylinders are fluid level switches in case you run out of brake fluid. They switch a light on the dashboard (normally a "!" symbolled light which is tested by the handbrake).

joemotion - 4/1/09 at 07:04 PM

thanks for your help everyone - just waiting to borrow my mates multimeter and will let u know how it goes!

I had a play with a piece of wire earlier on the switch however nothing happened so assume its not the switch thats faulty