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HOW TO: Modifying Carling Contura II SPDT for reverse operation


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Carling Switch Modification
This guide is to show how you can modify a SPDT Carling Contura II Switch to operate in reverse so you have 2 inputs and 1 output but still retain both the indicator LED and the Backlight LED while having the switch do what you want.....But as always, don't blame me if you use my info and destroy your lovely £10 switch :P

The Carling SPDT switch assumes it will be used to control 2 loads, whereas in my case I wanted 2 different feeds to control 1 load. The example used here is my roof mounted reverse lights. I want to have the functionality for the relay to either be switched on from a permanent 12V feed or automatically when the reverse gear is engaged. For this to work you have to use the SPST switch backwards from its design intent.

The Carling switches indication LED is wired to one of the output pins, so if you use that pin as a input the LED bar will in effect always be lit regardless of the switch position.
To help explain, here is a wiring diagram of how the internals of the carling switch are set out


  • Pin 1 is Output 1 (or 2)
  • Pin 2 is Input
  • Pin 3 is Output 2 (or 1, however you want to look at it)
  • Pin 7 is the earth for both internal LEDs
  • Pin 8 is the sidelight feed for the illumination window

Its a little backwards as when circuit 2 is armed the LED bar wouldnt light up anyway. What we need to do is re-configure the internal circuits so the wiring diagram does this


Now we have

  • Pin 1 is input 1
  • Pin 2 is output
  • Pin 3 is input 2
  • Pin 7 is earth
  • Pin 8 is sidelight feed

The modification really is quite simple, to do it youll need the following tools

  • Small electrical Screwdrivers
  • Drill and 1-2mm drill bit (small as possible)
  • Tweezers
  • Superglue
  • Soldering Iron
  • Needle nose pliers
  • some small solid wire (resistor leg)

First up then take one SPDT switch


Take a small electrical screwdriver and lever it underneath the 2 retaining tabs on both sides of the switch. As you do it keep some pressure on the 2 halves to prevent it springing apart.


With both retaining clips undone carefully relax the 2 halves to take the pressure off the springs


Now with the switch upright and at a 45 degree angle pull the 2 halves apart, this will keep the springs in the base and the roller rocker in place in the top half.



Here you can see the LED circuits in the top half, the silver wires are the positives and the golden wires are the earths. They connect to the base by sitting on pedestals which the springs push on to carry the current to the pins.

Next remove the roller rocker


Now we need to move the anode of the indicator LED, bit fiddly, use the tweezers and small screwdrivers to bend it up and away and move it across to the other pedestal


Now put the roller rocker back in and check it has full movement both ways and you havent blocked anything


Now move your attention to the bottom half


You need to move this spring from the location which takes the feed to indicator LED in the photo to the other half. On a DPDT switch the other half is taken up by gear so it leaves a convenient space to do other things on SP switches.

When you remove the spring you will also need to fish out the small cylindrical barrel, this is a resistor, not a diode, so you dont need to worry which way round it goes.


The plan is to drill a small hole next to pin 2 but in the opposite chamber, then run a link wire from the new spring/resistor location to pin 2.


You can just see the hole in the above picture

Now find a piece of wire long enough to go from the base of the resistor through the base and to pin 2, one side of a 1/4W resistor is the perfect length.


Bend it to this shape to hook into the spring base and go through the hole


And place it in position with the resistor and spring on top


Now you need to put the top back on to put pressure onto the spring to keep the wire in place IMPORTANT NOTE KEEP THE ROCKER AND THE ROLLER ROCKER SHAFT LEFT OUT!!!! Otherwise you will destroy the switch when you solder it!


Where the pin comes out bend it down and solder it to the base of the pin, just be careful not to put too much heat into the base, they are well made and as long as you have removed the internal components it should be fine.


Now take the switch back apart and put some glue on the wire to make sure it doesnt move on the inside and outside, however make sure you use it sparingly and ensure it has fully cured before re-assembly, air cannot get into the housing, so if it goes together wet, it'll stay wet! Re-assembly is the reverse of removal, use the 45 degree trick so it stays together while you push the halves together.


All done, the LED bar will now light up when pin 2 gets a signal and the illumination will work as normal. I do not plan to use the official connector blocks, so I don't know if these will work with the mod, chances are they will but you'll need to add a small groove to avoid the wire.


Figured I would do the write up as Im sure more than a few people will want the carling to do something similar.

Ive done it for 5 of my switches Front Fog, Front Spots, Reverse Lights, Voltmeter and auxiliary engine heater.


Hope thats all of some use to someone!

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That's a great modification! I'll be doing some of that!


:) Thought it might be helpful

Good write up!

Would it be possible to connect the additional wire to the base of the spade inside the housing, underneath the contact strips? I know it would take a lot of fiddling, but it would keep all of the mods inside.


It is likely possible, you could just run the wire down the other side, would be more fiddly and intricate and you would need to put some more care around how you route it to avoid the internal contacts for pin 1 and 3 and the rocker itself. Would need to take one apart and have a real dig. I'm quite happy with how this mod has worked so wouldn't go through the effort of trying to keep it all internal.

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see your point, IIRC I saw you are using the modular housings though.

Might use your idea, not sure though as I think the connectors do make it look tidier and less likely to have stray wires, but I have got 10 switches to install in my dash so cost saving would be noticable

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Mine will be tidy whether I use the blocks or not...blocks are nicer I will admit though!

Pretty sure the blocks will work with the mod too


Don't use superglue, it must let of off some kind of vapour, never had this problem before, must be the material the switch is made of. 4 of my modified switches are fine, 1 has a small build up at the base of the resistor causing it to insulate the connection. Will crack out the acetone tomorrow and rectify it. Just a note that to play it safe you are best to use a sealant or nothing as opposed to a glue.

I should note that the switch affected has a plastic roller, not a metal roller like the others so I think it's part of a revised design and the glue must have reacted with the plastic. It's not bad and a simple fix as I haven't fitted it, but it would be a right pain otherwise!

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I haven't got the switches with me now so I can't check but if I remember correctly the actuator will sit on the body in either direction, so yes you can but you will need to unclip the LEDs and swap them around, so they illuminate the correct parts, should be easy to do....either that or use a SPDT switch as opposed to a SPST switch and just only use one of the outputs, but would still rock twice.

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  • 11 months later...

I did something very similar with a spotlight switch some time ago so that when you flashed the full beam the orange led would light as the spots came on then as well.

This was as well as when you used the switch to put the spots on. On here somewhere.

Once you get brave enough to open one up you find they're very straightforward (apart from springs pinging off) and you can do all sorts of mods to get them to do what you actually want.


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Another thought. Would you be able to swap the illumination around so that the orange led is on permanently in the window and the bar lights up green when on?

My dash illumination is all orange so green switch windows slightly annoying

Yeah very easily, just unclip the LEDs and swap them around and bend the legs to suit

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