For the last 5 years I have been working on a '59 *****'s wagon that I built on a 2000 Blazer chassis and drivetrain. The project was really outside of my level of expertise, but I have been having a lot of fun with the project. I hope I can get some insights from the forum as to how to approach solving this problem. I am afraid I don't even know what I don't know.

I used 2 donors Blazers. both with 4.3L engines. The engines running well, it feels like the transmission is engaging when I shift into gear, but I am guessing that the transfer case is not shifting out of neutral.

Here are what I think are the pertinent details.

There were different transfer cases on the 2 different donors; I used the wiring harness from the Blazer with the 7-pin connector into the transfer case motor, but the transfer case I used doesn't have a corresponding female connector.

Every connector port in the transmission and transfer case I used have wires and connectors attached. There are no orphan ports or wires ( That I am aware of)

The lights on the 3-button 4wd switch do not come on.
If there is a difference between the TCCM's I may have used the wrong one.

When I shift into gear or reverse there is a slight decrease in engine RPM, So I think the transmission is engaging.
When I shift back into park there is a grinding sound

The wiring harness has a place for the (about)6 foot long harness connector close to the firewall penetration with the 7-pin connector to plug in, but I removed this 'jumper' because there was no place on the transfer case to plug it in.

I hope there is a path to success that someone could point me towards. I am shooting in the dark when it comes to troubleshooting the transfercase.

If you are interested you can view my build thread here.https://www.oldwillysforum.com/forum...17#post-262254

 

Yes the TCCMs and wiring and PCM programming is a lot different 3-button vs 4 button. All needs to match.

 

https://blazerforum.com/forum/2nd-ge...-blazer-89670/

https://blazerforum.com/forum/2nd-ge...-blazer-89044/

 

I think you are correct in that the transfer case is in Neutral.

 

Thank you for the documents and the help!I am always amazed at the expertise and willingness to help that is displayed in this forum. I hope I can return the favor someday!

I have quickly scanned the documents that you sent but didn't see the answer to this. Was the same wiring harness used in all versions of the Blazers in that period, or were there different versions?

 

Mine is a 4-button with two connectors at TCCM and two connectors at encoder motor on transfer case. I believe the 3-button version only has one at each. Also the TCCM interfaces with the PCM in the 4-button system and the front axle engagement system has an electrical solenoid inthe 4-button. However, just the other day I helped a person identify a loose 4WD connector near the PCM on a 2WD vehicle. So the evidence seems to vary a lot. This is an issue I have never dealt with.

Sounds like your wiring harness is for the 4-button Auto 4WD and you have 3-button controls and and transfer case? How many connectors on your TCCM and what color are the connectors in the TCCM itself (to ID the TCCM).

I would suggest comparing each circuit in the two sets of wiring diagrams that I posted. That's the only way you will know for sure if the 3-button to 4-button wiring harnesses are the same, but just some connectors unplugged or jumper harnesses added.

Since it is your vehicle, I will let you do that. If you get stuck let me know and I will try to help.

 

In the meantime, you can take the encoder motor off the transfer case and use a wrench on the shaft to click it into a different position to move the vehicle and test if trans and etc works. However I wouldn't drive this way and don't try to run the endoder motor to a different position by jumpering wires (that can ruin it). You will eventually need to put TC back into neutral to get the encoder motor back on.

 

After reviewing factory info (attached), it seems that harness is the same. However I cannot see the entire harness on the 3-button TC to know if some connectors are just not used. I suspect the 4-button might have a jumper harness that plugs into the main harness somewhere but I don't know this for certain. There are a lot more connectors attached to the 4-button TC.

Because your TC ended up in Neutral, I suspect the TCCM put it there when you first powered up. I am wondering if you are using a 4-button TCCM with 3 button controls and TC? How to identify the TCCMs are the photos.

The three button TCCM just doesn't use one of the connectors, according to the TCCM harness attachment. Likewise, the three-button TC does not require the electrical connection for front axle vacuum solenoid (it uses manual vacuum to/from a transfer case mounted vacuum switch). So the harness is the same at those two points. However I cannot see the entire harness at the 3-button Transfer Case in the attachment to know if some connectors are just not used. I suspect the 4-button vehicles might have a jumper harness that plugs into the main harness somewhere but I don't know this for certain. There are a lot more connectors attached to the 4-button TC that are not preset on the three button. Whether or not simply plugging the 4-button harness into the 3-button Transfer Case will work, still needs the wiring compared by the schematics. The kicker is that the PCM communicates with the 4-button TCCM but not the 3-button. What a 4-button PCM expects to see (if anything) may also cause an issue with SES/service 4WD light - but maybe not - it would not affect how a 3-button transfer case works (only throw up warnings and possible change how the transmission shifts).

For now please verify what you have for the following (3-button or 4-button):

Controls=??
Wiring Harness=??
PCM=??
TCCM=??



3-button TCCM



4-button TCCM

 

This is just what I needed.
It may be that I just need to get a 4 button switch. My Transfer and TCCM are both of the 4-button variety. and I put in the 3-button switch. All of the other connectors appear to be in place. I have ordered a 4 button switch, and I wil be trying it out tomorrow or Wednesday night.

The diagram for the front axle switch harness also solved another problem for me. I have been stumped as to where to plug in the vacuum switch for the front axle. You anticipated my next question.

Thank you so much for the direction. Now, I have a plan of action that I wouldn't otherwise have had.

I'll let you know how things work out!

 

I looked at your build thread. Looks interesting to me. Let us know if we can be of further assistance.