I'm working on a train layout and have built 2 automatic switches for the switch track. Each switch track is powered by M-Motor. I'd like to connect the 2 motors to a single IR receiver and battery pack with 6 AAAs. Unfortunately the longest extension cable I can find is 20 inches. I need a much longer cable than that; more like 8 feet. Is there a limitation to the length? Is it possible to make or buy such a cable? I'd like to avoid adding more Power Functions equipment if possible.
I found two independent tutorials how to create electronic contacts compatible with the original Lego contacts, which are located at two knobs of a 2x2 brick:
Two not-so-good (but where no LEGO parts are harmed) solutions for the sake of completeness:
You could daisy-chain a few extension cables; if you just need the one long cable in one instance it'll do the trick.
You could use older 9V cables (the longest being nearly 10 feet long) and converter cables. A bit awkward for a PF-based system, though.
I've been using both solutions when displaying GBC modules, as the placement of modules is always different and the length of the cables isn't fixed; but since the power source comes from a 9V transformer, it makes more sense to use also 9V extensions before converting to PF.
I'm not sure this would be the best solution for you, but it all depends on circumstances.