Testing the ALPHA 215C Data Cable ConstructionDisclaimer: Unless you are sure (or bold) about what you are doing, you could damage your computer, sign, or both.
Unfortunately, if you assemble a DB9 to RJ12 adapter incorrectly, attempting to correct the problem by disassembling the adapter may damage it. As such, it is possible to slide the female connectors over the male pins of a regular RS232 extension cord.
This allows you to experiment with the RX, TX, and GND pins.
Below is a snapshot of the adapter as I was trying out all the various permutations.
Adapter for for use with a cross over RJ12 and a ALPHA 215C sign.
The two center wires on the RJ12 (usually red and green) represent the RX and TX. You'll need to try both combinations.
The GND wire is usually one of the most outter pins available. The color of the wire will vary depending on where you're using a non-reversed or reversed cable, and whether the sign uses four pins or six.
If your sign has more than one RJ12 port, you'll need to locate which one is used for data communications.
Be aware that in order for the above wiring diagram to work, you must be using a reversing RJ12 cable.