Wired the same way as the Maplin style relays, I have installed the module behind the screen in the dash.
This position is preferrable as the aerial has a better chance of receiving a signal than if located under the bonnet.
Next the PAYG SIM was loaded with the approved numbers ( the SIM was set up in a mobile first) and the answering machine turned off. A mere £5 credit was put on the account and i was ready to go (the credit should last a few years at least)
Upon receiving an incoming call from a number stored in the SIM phone book, the module cancels the call after 3 rings, then when the relay has been energised successfully, the module calls you back to let you know that everything is ok. If you cancel this call, there is no charge, but if you answer once every few months, it keeps the account active.
The built in timer is set for 30 minutes and everything resets after that.
This way, I can call the car from anywhere in the world with a mobile signal, and my car will warm up, even in a carpark, and I will know that it is doing its job.
It's worked well for me lately ( certainly keeps SWMBO happy on a cold day ) and that alone is worth every penny.
Just thought I would share in case anyone else fancies an alternative switching method.
Happy days
