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Discussion Starter · #1 · (Edited)
So what is a "Mystery Switch"?

Very simple, it's a switch that allows you to manually control your torque converter lock-up solenoid. It lets you lock your torque converter in any forward gear.

Be cautious with this DIY. If you do not have a transmission that is built to handle some abuse, this modification can be damaging to you tranny. A good torque converter, billet input shaft and valve body, at a minimum, are suggested before using this mod.

The type of switch that you use for this is up to you. If your intent for this mod is towing or using it with an engine brake, I suggest using a toggle type switch. If your interest is racing or dynos, I suggest a push on, momentary type switch to keep you from forgetting it and stalling the truck.

So, on with the DIY......

First, you need to figure out where you want to put the switch. I placed mine so that I could lift a finger from the gear selector and hit the button. I decided to place it on the radio bezel. My switch is a momentary on type switch.



Once you have the location determined, you need to have the materials to do the install. A grand total of about $15 worth of electrical components is all that is needed. The biggest thing you my need to purchase, as most of us do not have these on hand is a pack of 33 ohm resistors. These resistors are necessary for this install, otherwise manually activating the TC lock-up solenoid will set a code and put the truck into limp mode.



Now we can figure out how we are going to rig this up. It's actually very simple, the most time consuming part is getting your wiring near and out of the way.

This is basically a two wire hook up. One from the torque converter lock-up solenoid wire and one to ground.

What this system does is GROUNDS the TC solenoid circuit.

Here is my basic diagram of how the system is rigged.



The wire we need to tap is the #7 pin on the transmission solenoid assembly. The wire is Yellow w/ a Light Blue stripe.





The connector that you need to remove is located on the drivers side of the transmission and is located directly above the dog ear for the transmission jack.



Once you have pulled out the connector and located the #7 wire (Yellow w/ Light Blue stripe), you need to tap into that wire. The method you use is up to you, I used a t-tap.



Once you tap the wire, you need to run your lead up into the cab. It is easier to feed the wire from the engine bay DOWN to the transmission. I HIGHLY recommend that all connections for this DIY are soldered and shrink wrapped.



Once the wire tap has been completed, you need to weatherproof it. I used a piece of 1/2" heat shrink tubing to go around cover the t-tap. I then went over that with electrical tape.





Once the lead is inside the cab, you can connect your 33 ohm resistor. This resistor is necessary, otherwise this will set a code and put the truck into limp mode. These resistors are approx $0.99 at Radio Shack. Solder your resistor to the wire and then connect the wire to your switch wiring.





Once the switch location has been determined and the switch is mounted, you need to conenct your wires to it. One wire is from the transmission and one goes to ground. Any clean, metal ground will work fine.











Once you have the wires connected to the switch, you are ready to put everything back together and try it out.



It's that easy.

Remember, keeping the TC locked at low speeds will bog the truck and stall it if you come to a stop. REMEMBER TO UNLOCK THE TC.

If you have a set of electronic gauges that shows the TC condition, you WILL NOT see the TC locked when you manually engage it. This is because the monitor gets it's signal from the TIPCM, not the TC itself.
 

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got one question for you, great install but why did you use a scotch lock under the truck(outside) and use heat shrink tubing inside the truck. sorry but i'm that guy that hates those dam things, i've found that using a butt connector with soe solder and the heat shrink tubing with glue works the best outside the cab. i'd do just the oppsite imo.

good install other wise!:thumbsup
 
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Discussion Starter · #3 · (Edited)
got one question for you, great install but why did you use a scotch lock under the truck(outside) and use heat shrink tubing inside the truck. sorry but i'm that guy that hates those dam things, i've found that using a butt connector with soe solder and the heat shrink tubing with glue works the best outside the cab. i'd do just the oppsite imo.

good install other wise!:thumbsup
It's all preference brother.

I've never had a problem with the T-taps when it's been a one wire hook up. Also, I didn't want to strip that wire back and expose anymore than necessary.

I used the shrink wrap inside the cab because of the likelyhood that those wires and connections would come into contact with other wires / metal surfaces.

Also, I used 3 layers of shrink wrap over the resistor to stiffen and reinforce it a bit.
 

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some other thread told me to put the 33 ohm resistor on the ground side? no wonder it never worked.
 

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im going to try and put the resistor on the other side, but as of now it doesnt work for me :(
 

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That is a great write up - thanks. It even includes the famous last words "Its that easy"! LOL!

It complements the other TC lockup write ups in the 3d gen Tech Article section by providing additional pics/install info. Maybe you should submit this as a Tech Article...

My question is how to wire 2 of these switches - one could be out in the open for towing/racing etc. and one could be hidden as a security device - the truck wouldn't go anywhere in 1st gear with the TC locked, right?
 

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What are the benefits of locking the converter, I thought it locks automatically?

I have an exhuast brake already on the truck, how does locking the converter help?

Used to driving a stick,never had to worry about this stuff..
 

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when i did my switch i never put the resistors in it. i get the code but its not in limp mode and i have had for almost 2 years. if i put one in with it get rid of the code.
 

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Discussion Starter · #12 ·
when i did my switch i never put the resistors in it. i get the code but its not in limp mode and i have had for almost 2 years. if i put one in with it get rid of the code.
If it's a soft code, it'll go away after X amount of cycles that it doesn't see the problem.

Otherwise, just go to AutoZone, Advance, O'reilly's, etc., and have them clear the code.
 

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Discussion Starter · #13 ·
What are the benefits of locking the converter, I thought it locks automatically?

I have an exhuast brake already on the truck, how does locking the converter help?

Used to driving a stick,never had to worry about this stuff..
Basically this mod allows you use your tranny as a stick.

The only time the TC locks normally is in 4th gear. In T/H mode, it will lock in 3rd.

This will allow you to pick a gear and lock the TC in 1st or 2nd.

It's a GREAT mod for exhaust brake use if yo udon't have one of the stand alone controllers.
 

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Ive read about it being necessary to jump two pins on a transmission relay underhood to prevent a CEL, any thought on this?
 
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Discussion Starter · #15 ·
If you don't use the resistor, you need to pull the tranny relay (#59) on the earlier 3rd Gen trucks. If you use the resistor, you don't need to jump the relay.

You can install the switch without the resistor by jumping post 30 to 87 on that relay.
 

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two of my buddies, both with 04.5's, installed lockup switches as mentioned, without a resistor or jumping the relay. The same thing happens to both of them, it locked up the first time, then never again, and the truck ran like (limp mode?) but no CEL...?
 

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Great write up:headbang: you can also do it another way by putting a diode one the ECM side of the TC lock up wire. just my .2cents. Other whys yep its that easy folks haha
 

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got one question for you, great install but why did you use a scotch lock under the truck(outside) and use heat shrink tubing inside the truck. sorry but i'm that guy that hates those dam things, i've found that using a butt connector with soe solder and the heat shrink tubing with glue works the best outside the cab. i'd do just the oppsite imo.

good install other wise!:thumbsup
I agree, I would NEVER leave something like that where moisture can get to it. VERY bad idea. If you had to use this type of connector there I would at least try to weatherproof it somehow.

Other than that, GREAT writeup with pictures...So easy a caveman can do it!
 

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Discussion Starter · #20 ·
I agree, I would NEVER leave something like that where moisture can get to it. VERY bad idea. If you had to use this type of connector there I would at least try to weatherproof it somehow.

Other than that, GREAT writeup with pictures...So easy a caveman can do it!
Okay........

After I installed the tap and connected the wire, I used the 1/2" shrink wrap on it and taped it over to weather proof it.

No, you not just want to leave it exposed.
 
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