I have a Ford mini compressor kit with tyre goo for punctures, which I carry in the Plus 6. It uses the standard male type power connector that goes into a cigarette lighter socket. In order to get around the power needed I found on ebay a female connector with several metres of extension lead and crocodile clips on the other end. As a CX gen cars battery is easy access under the bonnet you can clip it to the battery terminals directly and still power a small 12v compressor. The only word of warning is to make sure the extension wiring is big enough for the power draw needed. The variants from China were too small a wire gauge, in the end I purchased one that was made in Germany, slightly more expensive but it was rated to handle the power draw.
