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Discussion Starter · #1 ·
Hey Guys, new to the site, and I have some questions about hard wiring the shift motor on an MP3023 transfer case.

A little back story, I recently inherited a project from a relative (8 years in the making and counting). It is an '82 GMC Sierra Classic on a 2011 4x4 chassis. it is an LC9, 6L80E with the MP3023 transfer case. Very long story short, I do not have the TCCM to control the transfer case (burned up with the cab of the donor), but I do have the harness for the shift motor and 2/4 indicator (my guess on that one). Has anyone been able to hard wire a dpdt switch with 25 relays to activate the 4-high and 4-low on one of these things?

I have seen where everyone usually just swaps out the MP3023 for an NP241C. I have one on hand, but I am needing more of those green pieces of paper that everyone loves so much to get a new input shaft and get a rebuild kit for it.

Right now I have a 4wd truck with no 4wd, and it makes me upset. Font axle activation is not an issue, I found how to do that, but it seems like no has done or has tried to do a hard wire set up on this. I have looked at several sites and YouTube university and came up empty.

I found a wiring pin out on a tech write up that has the Red/Black wire as battery voltage, Tan is motor A control, and Orange is motor B control. I am guessing that Tan and Orange are grounds since there is only one power wire. The smaller Tan wire is a lock solenoid control, which is what I am guessing holds the clutch fork in place. Pins E through H don't affect me since I don't have the TCCM.

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The truck is still a work in progress, so don't judge it too hard. Did I mention that I am limited on funds for this project?

Any assistance with this would be greatly appreciated,

Big Al
 

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Looks like a/b are your motor dirrections
E-h are your indicators (2/n/4h/4l)

So a single relay to the +(ko/er) with a double pole double momentary (on)off(on) switch to provide grounds will prob get you running.
 

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Discussion Starter · #3 ·
Looks like a/b are your motor dirrections
E-h are your indicators (2/n/4h/4l)

So a single relay to the +(ko/er) with a double pole double momentary (on)off(on) switch to provide grounds will prob get you running.

Thanks for the reply.

I was under the impression that the battery positive would be power for all of the motors and possibly the lock solenoid, and that the larger tan and orange would be the grounds for the motors. Give motor A a ground and it would activate. Same for motor B. The relays would allow a high current ground for the motors.

E through H I think give feedback to the PWM control (TCCM).

Not sure if only motor A is needed for 4 high, motor B for 4 low, or if A and B are needed for 4 low. Also not sure about the lock solenoid. Read in the tech article that the voltage is removed from the motor and a solenoid holds the TC in the selected gear.

There is another plug that said 2/4 wheel drive (smaller plug on the harness). Guessing that one is for the 2/4wd indicator.

I do not a service manual to look over, so I am only going off of what info I can find on line.

Again, this is all a guess on my part. Does that sound like I am heading in the correct direction or going on a cold trail?

Big Al
 

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Discussion Starter · #5 ·
Got ya. Guessing A is "in" and B is "out". The articles I have read said that it uses an encoder to tell the TCCM where the shift fork is. I will try to post a link to the articles here when I get back to my computer (thumbs are too big for my phone keyboard).

Al
 

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Discussion Starter · #6 ·
Ok Folks,

Below are the addresses for the articles that I have been using to try and figure this out. I work better with one on the table so I can move things around to make sure I understand how it works but that is hard to do when you are driving it. It would be really nice if I had TC on the table and see what happens with power applied.

I think I have the brake solenoid figured out. It should be locked without power and free when power is supplied. I would need a momentary switch to power it when switching from 2wd or 4wd drive, then just let go to lock it into gear.

The hard part for me to wrap around is the High/Low shift and front axle engagement. The article talks about the TC uses a clutch to engage the front axle. So for that part, it should be a simple matter of applying voltage to the clutch motor for full engagement (not worried about slippage for turning). The High/Low shift is the hardest part for me. I am not sure what the shifter is activated with or how to tell what range it is in.

I am guessing that for 4H, all I would need to do is energize the brake solenoid (or would I since it is already in High range), engage the front axle clutch pack, then de-energize the brake.

For 4L, energize the brake solenoid, engage the front axle clutch pack, shift to low range (however that is done), then de-energize the brake.

Since there is only one battery positive in the harness, I am gonna guess that the smaller tan wire would be the ground for the brake solenoid.

Does that sound like I am heading in the right direction?


I am open to suggestions,

Al
 

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That Magna case has a lot of controls associated with it and it doesn't sound like you can do everything manually at all. I'd look for a manual shift equivalent (1226?) or put in your 241. This thing won't even lock into 4wd conventionally since the front drive is computer controlled to lock the clutch pack. Maybe full time 12V applied to the correct pin will just lock it solid and give you front drive but maybe not. It also doesn't have anything but the shift motor to lock it in gear so without feedback on where the motor is, you have no idea where to stop it. These things are kind of a mess in the vehicle they're native to.
 

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Discussion Starter · #8 ·
That Magna case has a lot of controls associated with it and it doesn't sound like you can do everything manually at all. I'd look for a manual shift equivalent (1226?) or put in your 241. This thing won't even lock into 4wd conventionally since the front drive is computer controlled to lock the clutch pack. Maybe full time 12V applied to the correct pin will just lock it solid and give you front drive but maybe not. It also doesn't have anything but the shift motor to lock it in gear so without feedback on where the motor is, you have no idea where to stop it. These things are kind of a mess in the vehicle they're native to.
Yeah, the more I have been thinking about it, I am just gonna move on and get the 241 rebuilt and put in.

The encoder was the hold up.

Thank you for the input. It was much appreciated.

Al
 
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