I just did this swap in my 00 Blazer. I got a console from 98 via ebay (make sure they include the other side of the harness!) ...

I had been looking around for a full size charcoal colored console to replace the one I have... when I received the new one it was dirtier then mine, so I started to look into whether I could pull the trip computer module to swap the new into my old... of course as it turns out it's DEAD SIMPLE and if I had bothered to look that up first I could have bough any console size or color I wanted which would have opened up some cheaper options for me, oh well

Anyway, what I was able to do was individually pull all 6 of the conductors out of the older 6-pin compass harness and then insert them into the correct position of the 9 pin trip computer harness, that way there aren't a bunch splices up there waiting to fail... what I did was to look at the connector, I saw there was a red piece of plastic piggy backed on it, I pulled that and I found that the plastic had 9 little "fingers" on it... well if you flip it around and insert it into the other end (one finger at a time), it will release the individual conductors (be careful and example closely before you do this!)... Anyway, it took a few minutes to figure out, but then I was in business pulling the conductors from both the 6 and 9 pin harnesses, I'd suggest you practice on the 9-pin harness first, if you screw up a wire or conductor there it isn't too bad since you won't use 6 of them anyway. The end result is that you only have to do 2 splices up there, one for "Yellow" (data bus) and one for "Orange" (+12 constant).

I got the +12 constant from the map light wire of the other harness up there, it was also orange so I took a guess, tested with my meter, and found I was all set... just make sure you have the dome light override on so you make sure you are getting +12 and not dome light power.

Then I routed a new 16# wire down the A-pillar (I zip tied it to the existing foam covered harness there) to under the driver kick panel and then spliced to the back of the OBD-II connector purple wire, then up a the overhead console I used a butt connector to connect that to the existing yellow wire of the 9-pin hardness (do this part LAST in case you f&$k up running the wire...)

I plugged in the trip computer, started up the engine, set it for instant economy then rolled back/forth in the the driveway to see the numbers go up... I waited another minute or so because I heard someone say that there's a pre-97 to post-97 issue, well knowing I had a 98 computer and 00 truck I figured I'd be ok, but better safe than sorry... after that I buttoned it all up.

I had to leave for a trip at 10:00AM... I started this job at about 8:50AM, and was interrupted at one point to talk to a neighbor for a bit, so all in all I'd say it took me under 60 mins to complete the entire job from start to finish...and I never opened the hood or pulled a fuse.

I needed a 9/32nd socket to remove the kick panel bolts under the dash and unscrew the OBD-II connector from the panel (not needed but made it easier to get that purple wire).... a #2 (or maybe it was #3) Phillips to remove the console from the ceiling... and a pair of lineman's pliers with the little crusher thing to complete the butt connector on the yellow wire and crush the splice taps. I also used about 8 small zip ties around each splice and a few other places to keep things in line. I pulled the existing electric tape back from the harness and used that to wrap over all the splices, then zip tied over it to hold it in place.

BTW, I ended up I getting 22.3MPG average on my trip across the state yesterday... which at $3.839/G makes me want to trade her in for a Civic or something that gets better mileage ...