Say, I might have found the pinouts online. Or some version of them.

This is for a limited edition 2000 Honda (not an Odyssey), but the fuzzy pic of the connector looks extremely familiar to me (Paul, do you concur?). That the pic of his head unit looks practically identical to mine has me even more convinced it's the one. Can't be 100% sure, but I think it's a good bet.

Here's the chart:

Pin	Function	Color	Pin	Function	Color
1	Antenna/Remote Amp Relay	Yellow/Green	11	N.C.	-
2	12V Accessory Power	White/Red	12	N.C.	-
3	Dash Remote	Green/Red	13	N.C.	-
4	N.C.	-	14	Mute	Yellow/Blue
5	Right Rear Speaker +	-	15	Right Rear Speaker -	-
6	Left Rear Speaker +	-	16	Left Rear Speaker -	-
7	Right Front Speaker +	Green/Black	17	Right Front Speaker -	Light Green
8	Left Front Speaker +	Green/Yellow	18	Left Front Speaker -	Gray/Red
9	Illumination Signal	Red/Black	19	N.C.	-
10	12V Memory Backup Power	White/Blue	20	Ground (chassis)	Black

Hmm. No dimmer though. Just illumination. But the Crutchfield harness I have has a dimmer wire. Ehh ... maybe this isn't it, but it's got to be close.