These may be of use Ray, if you can read these things. PDF printer wouldn't print as one job.

Thanks Sean.
The circuits that I was looking for are the internal ones for the unit.
I have now worked out where I can do this.
All I have to do now is pull my unit out, solder two wires onto the circuit board, refit the unit and connect the receiver to the two wires and test it.
Might have time on Saturday.

Here is Ray's excellent write up for his Webasto Heater Remote Control Retrofit!
Take a bow Ray and thanks for the detailed write up!
+++

Makes it sound easy. Have you seen the size of the mounting points that you have to solder to? The last time I attempted something like that was when we had to solder chips onto DVD players to make them multi-region.

What Neil said.

Well done Ray +++ Nice write up, you've raised the bar!

I love it! thanks