15 replies to this topic

[gixernick]

As the title suggests, I have a Digital multimeter but electrics aren't my strong suit.

[R1minimagic]

The switch is self testing, just press it and it should light up

[gixernick]

Not sure I understand that. The brake lights don't work and I want to check the switch thats in the hydraulic line. Is there some way of doing this with multimeter?

[L400RAS]

Some confusion here; you are meaning the switch at the base of the brake pedal itself, that activates the actual brake lights. I would check that you have 12V incoming with the ignition on, and that you have 12V out of the rear of the switch if the brake is pressed. If you have these, then the problem is elsewhere - usually the actual connectors in the boot.

[gixernick]

No its a 1977 Clubby and the brake light switch is in the hydraulic brake pipe and operated by pressure. Or so I've been told ?!?

[Dan]

The brake light switch was changed from hydraulic to mechanical with the major electrical upgrade for the Mk4 in 1976, your brake light switch is at the top of the brake pedal and probably just needs to be adjusted. Unless your car is actually older and registered late.

To test either switch, first check for 12v at the supply side of the siwtch as said above. Then disconnect the switch completely and set the meter to continuity or resistance (ohms or beep test). You may have to set more than one control for this. Check the meter is working by shorting its probes together, it should beep. Connect the probes to both terminals of the switch and apply the brake, if the meter beeps the switch is fine.

[Spiffingly Good]

Maybe clubbys wern't included in the electrical upgrade.

I have a 78 clubby and the switch is a pressure activated one in the brake lines. Also haynes list clubman wiring differently to saloons, maybe there is a difference.

Edited by Spiffingly Good, 12 September 2011 - 08:23 PM.

[Dan]

There really shouldn't be any difference. The upgrade was across the range as part of the Mk4, how many fuses does your car have in the fuse box?

[gixernick]

Definitely a hydraulic one on mine just been and checked.

[gixernick]

Four fuses

[lrostoke]

so if it really does have the switch which will be left side of engine bay just above where front flexi hose comes through the subframe.

Two spade connections. unplug the wires, ignition on

Turn mulitmeter to volts a range that covers 12v DC
Attach the black wire of multimeter to a good earth point, attach red wire of mulitmeter to either of the wires you unplugged and look for a voltage if one gives a voltage then thats power in to the switch.
If no voltage then problem with feed getting to the switch.
If you did get a voltage connect that wire to one of the spades on the switch, connect red wire from multimeter onto the other spade and press the pedal. If voltage goes to 12 switch is ok.

Actually a real simple way of testing the switch is to just connect the 2 wires that are on the switch , if the brake lights come on, problem is the switch

Edited by lrostoke, 12 September 2011 - 08:42 PM.

[MEhinger]

Gosh, all those replies and it took until Irostoke to finally get the answer. Do his simple test. Touch the wires together. If the brake light come on it is the switch. If not then use your multimeter to follow the wires, probably to the fuse.

[lrostoke]

It took me till I'd typed all the multimeter stuff to think you soft sod join the wires ha ha

[gixernick]

OK checked and its not the switch. I've also turned the ignition on put the black wire on a good earth then checked all of the four supplies to the fuse box. Top thre all have 10V or more each the bottom one has nothing. I'm assuming this will be the problem

[gixernick]

Got no power at all, switched or otherwise, to the bottom fuse red/green one side red the other.