Hey Mongoose...
The channel mod is very easy on this thing.. If you remove the speaker side cover, look to the left side of the pc board (with the radio front facing you).. mounted to the board you will see 2 white jumper blocks and 1 brown one... Slightly to the right of there, you will see 2 more white jumper blocks and 1 brown one.. the jumper blocks are set to where they only plug in correctly... Move the 3 sets of jumper wires to the other 3 sets of blocks, then the dimmer control will work for high/med/low
Here is a link to the conversion.. the picture isn't that great, but if you can't get it let me know and I will take pictures of my actual radio for you.
/http://www.cbtricks.com/radios/rebel/tx500/graphics/rebel_tx_500.pdf (remove the / before http to make the link live. At the site I moderate at, live links to other websites are not allowed)