How to wire in a mechnical brake switch in to your mk1

[Spyda]

I don't know how many people will find this use full but here it is for anyone that's interested. I hear that the hydraulic switch on the mk1 tend to fail a fair bit and this is a piss easy and solid solution for thous that want to avoid replacing their hydraulic brake switch on the master cylinder. I assume it would also save time having to bleed the brakes.

My brake lights have been working intermittently for a while so i decided to sort it out before someone smashed in to the back off my mk1.

Start by making sure it your hydraulic brake switch that is faulty and not a fuse or loose earth. To do this simply unplug the lead from the brake switch on the master cylinder and either jump the red/black and red/yellow wire to make the lights come on or do a continuity test with a digital multimeter (DMM) across the switch while someone presses the brake pedal.

If your light still don't come on when you jump the two wires then something else is the problem, check the earth in the boot or the fuse.

If it is your brake switch its easy to install a new mechanical brake switch on the pedal box. You will only need a few parts and a couple of tools. You can get them all at Jaycar. Parts cost about $17.
You will need:

1x SPST 30a Relay (Cat no: SY-406 (You can use a fused relay but i don't think its necessary)
1x Metal tamper switch (LE-8776 comes in a pack of 2)
2m of ~18 gauge wire.
Some spade connectors
Some heat shrink or electric tape.

Tools:
Crimper or pliers
Cutters
Wire Strippers (makes life so easy) $15 for T-rex style
Screw driver
2x 12mm spaners
Drill with a good size drill to make a hole for the switch.


You wont need this many



Start by disconnecting the plug from the brake switch on the master cylinder. My switch had 3 pins, some have only 2. In the case of having 3, you will leave one out, i did and it work. You will need to permanently connect the two wires by either cutting and joining the two or creating a little jumper. Since i don't like to needlessly destroy things i made this and plugged it in.



Next remove the screw holding the fuse box in place and move the fuse box so that it faces down and you have access to the wires behind. Following logic you are looking for the same color wires as on the switch. I checked the Haynes manual wiring diagram and you should be looking for a red with black stripe and red with yellow stripe. Red/black (neutral) is found on the first loom and red/yellow (12+) should be on the third.


As you can see i have already cut one, the other one i striped back a bit so i could use a DMM to make sure they where the right wires.


I cut red/black as this is where you will be putting the relay. Strip a bit back and crimp on a couple of female spade terminals. Unplugging it makes it easier.


Next up, connect thous two spade terminals across the switching points on the relay.
Then get a short bit of wire and attach a spade terminal to one end and plug it in to one of the coil points of the relay. Attach the other end of that wire to a 12v point, i just taped in to one of the many red 12v wires on the fuse box. Make sure its a constant 12v.
Get the rest of your wire, about 1.5m should be plenty, and put a spade terminal on one end and join it to the relay.
You should have something like this. (Please note that i am holding the relay 90degress clock wise to the diagram below)

Here is a simple diagram:


Now you can touch the 1.5m wire to an earth point to check that everything works, you should hear a click from the relay and the brake lights should light up.

If its all good, feed the wire behind the fuse box and make sure all connections are tight before refitting the fuse box.
Once the fuse box is in place feed the wire under or through the dash to the brake pedal.

Next up get the drill out. You should have a bit of metal in front of the brake pedal as some US mk1s came with a switch as standard (according to haynes). Simply drill a big enough hole to fit the switch in to.
Make sure that the hole lines up with the brake pedal and don't drill it to high. You should probably drill it lower than i did.
No hole:


Put the switch in place and loosely secure it with the nuts provided. Depress the pedal (I used the drill as a weight) to remove the free play and adjust the switch so that its tightly secured and touching the pedal. Get your 12mm out and tighten it up.

You should end up with something like this, but hopefully lower.


When you depress the pedal the switch should be closed.

[Spyda]

Now simply trim the wire, crimp on a spade terminal and attach it to the end of the switch. If its tight wiggle it on, don't push or you might brake the switch.



Test it out, make sure it works and you should be all done.

I reckon thats pretty easy and fairly stupid proof, i mean shiz i managed to do it.
Sorry for the bad pictures btw, my camera ran out of batteries.

Hope it helps a few people.

[Spyda]

Can some one change the 'an' to an 'a' in the title.

[GRN_VAGN]

looks good,

Will take a pic of mine for reference too... I used a Falcon XF brake switch, custom bracket to bolt to near pedal.
cut wire behind fusebox and made a new loom to switch... works great

[GRN_VAGN]

found pic



Ugly, but it works, only did it cause i got a bigger master cylinder and ditched the stock sensors
Also, a relay is not needed, just wire the 2 wires directly to the switch, its already fused and will be fine saves wiring, but good detailed write up

[Jarred]

As Grnvagn mentioned, you need to do this upgrade if you go to a later model 4 port master cylinder,

it is pretty straight forward, and there are a couple ways to do it. (I used a VW switch from a mk 2 for example, with custom bracket)

This way seems pretty straight forward, and is relayed too (mine wasn't)

Thanks Dado for the write up!

[Spyda]

found pic

Ugly, but it works, only did it cause i got a bigger master cylinder and ditched the stock sensors
Also, a relay is not needed, just wire the 2 wires directly to the switch, its already fused and will be fine saves wiring, but good detailed write up

I know a relay is not needed but because the switch i was using switches negative it was the only way in my case. It was a bit urgent and didnt have a switch where a relay wasnt needed. You can avoid using a relay if you have a switch that is 'normaly closed' and momentary, we dont sell one large enough at Jaycar so sourcing one from another car is the go.

I also can't make a braket like that because ive got the carpet cover that goes under the dash, the little gold bit of metal with the clip on it is what holds the carpet on.

Ive got stacks of wires under the dash (dvd player, electric windows, alarm etc.) so i didnt want to add more than i needed too aswell.

[GRN_VAGN]

Too easy, i dont have the carpet and i didnt really care what it looked like, aslong as it worked

[Jarred]

I had the carpet, my bracket still worked. it's do-able

[Volksee77]

Good idea, i have a similar concept or though an entirely differnt switch on my rally car but you can actually use the stock wiring from the actually plug which normaqlly clips to the master cylinder switches this way it's one less bastardisation on a mk1 wiring loom