on the current vehicle  conversion , the spec requires  locking differentials with a air  compressor of the ARB style,

not wanting to stick the big ARB/Carling type switches in the dash panel like this

Standard fit ARB switch panel

Standard fit ARB switch panel

 

or even like this

 

A bit neater but still not OEM is it?

A bit neater but still not OEM is it?

so I decided that I would look into converting the OEM range rover switch that was no longer needed as we now have good old coil springs fitted.

Range Rover P38 AES air suspension switch

Range Rover P38 AES air suspension switch

 

now this switch is not just any old switch it is a electronic communication switch that talks to the BECM, so som mods had to be done,

A quick look inside and the wiring diagram showed promise

Simple little thing she is.

Simple little thing she is.

the buttons that are pressed by the rocker switch come out on pins 8 & 6, the button illumination is standard, so just need to control the LEDS.

 

the Idea is that the rocker switch will select what is on/off  of the  Air compressor/ rear diff lock or front diff lock, and also give an indication that the compressor is working via a simple feedback.

OFF

OFF

Compressor only, the LED will flash if the air tank is not up to pressure

Compressor only, the LED will flash if the air tank is not up to pressure

Compressor and rear diff

Compressor and rear diff

Compressor, rear and front diff locked

Compressor, rear and front diff locked

at any point when the compressor is ON and the tank pressure switch clicks in to engage the pump the Compressor LED will flash, this lets the driver know the compressor is working, over the years in Dakar the noise in the car and wearing helmets means its not possible to hear the compressor run, if a pipe to any diff fails the compressor runs constantly and burns out, result = no diffs locked = stuck or a bust diff, so this feature is really important for reliability.

 

so how does it work, I used a PIC16f628 microchip and a ULN2003a darlington transistor array, cut the track to the LEDs , soldered them inside the OE switch case and knocked some code up and in one night I had an Air locker diff control module that is OEM looking and fits perfect, and also easy to bodge/bi pass in the event of failure, which will never happen will it 🙂

 

This is the test wiring before the PIC chip is glued in

This is the test wiring before the PIC chip is glued in