Aha! After a very helpful tip from a gentleman on the TUNFS forum (reg required), I've found the wires. For anyone else with a Nissan Frontier, they're yellow with red stripe and yellow with black stripe. If I read the multimeter correctly, I believe the resistance values I get are the following:
Code:
Vol Up 23 ohms
Vol Down 91 ohms
Up 602 ohms
Mode 337 ohms
Down 195 ohms
I forgot to check what the resistance of the open circuit is, but it's >2000 ohms, at any rate (I'd go back out and check, but I've already put my truck back together). So, I guess my next step is to figure out what I'm supposed to do with those values. 