I leave my connections permanently wired between the mount and the observatory PC. So from mount and power on the mount will be getting slew commands from the parallel port if its not been last written by nulls - yucky.
glasseyes
If you're going to wire the serial port to the autoguider rather than the hand controller (and I do both for different purposes), use RJ12 wiring and -
be very sure to use electro couplers with the right resistors / diodes wired the right way to prevent damage! This is what the shoestring products does (probably using 2-3 resistors, a capacitor and maybe an inductor in the right place). Alternatively you can try a design using two diodes
http://www.bbastrodesigns.com/autoguide.html
You can find wiring diagrams on the net, it isn't as simple as RS232 pin 3 goes to pin in 1 of the autoguide port, the volatge and ampage and impedance have to be altered from the serial out to the autoguider in!