Wiring the NP-233 T-Case with 3-button control

I thought I'd put down in one place what I did to hook up the electronic controls for the np233 transfer case installed in a later model Astrofari…. I see the question come up from time to time, and I certainly had questions when I went to do it, and I couldn't find the answers any one place. So maybe this will be helpful for someone.

I started with a thread on the other forum that detailed the installation of the 233 with 3 button controls in a gen1 Astro… That was helpful, but there are some differences in the later models….

Let me just say that I don't know for sure whether this will work for you, I just know that the following worked for me. My van is a 2004 Safari AWD, into which I swapped the t-case out of a 2000 Blazer. The physical install was bolt-in, and required no mods.



So now, to make it work. I chose the electronic controls because I don't have welding and metal fab skills to make a manual shift setup, but I do know how to connect wiring together. I extracted the 3-button switch, encoder motor, TCCM and as much wiring as I could get from a 97 Blazer. I took the dash apart in the donor car and removed the full harness - this saves building it. For reasons I will discuss later, I would suggest using the setup from a 98 and later Blazer instead.

I found that the full Blazer harness gave me enough wire to install the switch to the right of the speedo, the TCCM under the driver's seat and run the encoder wiring out through the grommet in the floor (by the B pillar) that the original AWD wiring ran through. I like having the TCCM there because if it breaks, it takes 1 minute (if I'm slow) to swap in a spare - this put my mind at ease about possible unreliability issues. Once all the wiring harness was threaded into place, it just remains to connect it.



SO this pinout chart is the basis of the hookup.



Most of the wiring is internal to the system, which is why the entire harness is a blessing - it just leaves a handful of external connections to be made. The external connections are:

C1 - 4Lo signal - more on that later
C6 - battery power
C8 - Ignition only power
C10 - ground
D2 - PNP switch output - positive
D3 - TCCM diagnostics
D8 - VSS signal
D10,12,13 - grounds
D14,15 - battery feed
D16 - either PNP signal ground, OR crank feed.

I did a lot of head scratching to figure out D16 - how could it be both positive and negative? Also, just where do you get the PNP signal from, since the Astro has a different switch configuration? Then I found this diagram for the 1999 Blazer and all became clear.



Later Blazers use a PNP switch much like the later Astros. The PNP signal actually runs up to the stoplight switch, and that's where to find it. The earlier electronics, like I had, use a second (ground) signal from the older style Neutral Safety Switch that is not present on later models (of Astros or Blazers)…. Later Blazers use the crank feed in this location.

So, with the wiring harness threaded into place, it's time for some connections. The way I routed the harness, all of my loose wires from the TCCM ended up along the driver's kick panel area, so I looked for as many of the hookups to be on the convenience center (CC) as possible. Here goes:

C6 is connected to the courtesy light circuit - I used the wire running up to the visor vanity lights at the upper left of the CC.

C8 is connected to a pink wire found at the steering column running from the ignition switch.

C10 & D10,12,13 are connected to the old AWD system's ground in a plug on the CC.



D2 connects to the PNP wire found at the stop lamp switch - it's a light green wire.



D3 is left unconnected - I found out after much head scratching that if the diagnostic signal is hooked up, it disables the TCCM. Leave it disconnected and then, to run the TCCM's diagnostics, hook it to ground and the codes are read from the flashing of the lights in the switch….

D8 is the VSS signal - If you have the overhead console, with DIC (trip computer), there is a signal running up it that can be found on the DIC plug in the convenience center- look for a dark green wire with white stripe. This signal may also run to your radio if you have the speed control volume feature. If you have neither of those, then you probably need to pull your gauges out and find it in there.



D14 & D15 I hooked to the power feed for the AWD at the plug in the CC.

D16 - since I had the earlier Blazer TCCM, I connected this to the e-brake switch down in the kick panel - to shift into 4LO, I would apply the e-brake, which grounds that wire….

Later, I switched to the TCCM from a 2001 Blazer, which required that I change this. I found a crank feed in the back of the fuse block - a purple wire that's by itself (position E5 below). Now, to engage 4LO, I just put it in neutral at a near stop and it drops right in.



What about C1? It goes to the PCM and this pinout for the 2001 Blazer PCM connector C2 shows what is needed:



The Astro uses the same basic PCM connector configurations with just some minor differences in what wires are hooked up - one of those being position 16 on C2 - that's where that 4LO signal goes - on Astros, it's empty.



I haven't hooked it up yet on mine. It's purpose is to allow the tranny to upshift at lower vehicle speeds, so you can get all 4 gears in 4LO. With it unconnected, you only get 1st and 2nd. Next, the switch.

I was unhappy with the choices for mounting the Blazer switch, which is very strange, in the Astro dash, so I found a 3-button switch used in Tahoe/Yukons from around 95-98 or so that I thought I could fit into the space below the right A/C vent. Well, there's not really enough space there, but I made it work out...

Here's the Tahoe switch:



Basically, the left part of the switch doesn't contain any circuit board, so I cut it off.



Then I modified the A/C outlet by removing the lower vent:



Then I added a piece to the instrument panel face:



And then I rigged up some fairly cheesy hocus-pocus behind it all to hold the switch in, cleaned up the evidence, and from the front, it looks about right



That particular switch uses the same inputs and outputs as the Blazer switch, so integrating them was easy. Only difference is that the Tahoe/Yukon switch adds backlighting, easily tapped into the dash lighting circuit.

The part with the switch actually took longer than the whole rest of the conversion, but I'm happy with the final product:



And the super-good news is that it works!

Except for the backlighting bulbs, which are, of course burned out.