Hi Everyone

I am written to pick up some advice from you on a project that was presented to me.
i am working a design that would be fitted in trallers . the aim of the project is to have an Lcd display in the cab of the lorry that would tell the driver the lenght & High of the trailler
on the display.
BUt it is not as simple as if sounds.
i client does not want ANY wire connection between the cab and the trailler and does not want to use wireless.
The way he wants this to work is that there would be 2 units one in the cab and the other in the trailler.
The unit in the traller would be programmed with the lenght & High etc at programme time and the data would be stored in the internal eeprom of the pic.
so all the trallers would have there data stored there so they can be used with any cab.
The data stored in the traller would need to be sent to the unit in the cab
But there is only a single wire connection between the cab & traller (Which is the reverse line when not in use)
Question How can i communicate between the pics using a single wire to sent the data
is this posible or is he asking for too much.
Personally i would go for wireless using RF modules but he dont want any cable to be touched apart from the line i talked about.
Is there a way of doing this regards

Isaac