47RH/NP241 swap (replacing A518/NP205) SPEED SENSOR connection HELP - Dodge Cummins Diesel Forum
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Old 11-13-2010, 08:02 PM   #1 (permalink)
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47RH/NP241 swap (replacing A518/NP205) SPEED SENSOR connection HELP

I'm in the final stages of the swap and stumped by the speed sensor connection. The A518/NP205 speed sensor in the 1993 truck has a 2-wire connection whereas the 47RH/NP241 has a 3-wire connection.

1993 Two wire on the NP205: BK/LB is the common sensor return to the PCM (pin 4), and WT/OR is the 8 volts from the PCM.

1995 Three-wire on the NP241: 1-WT/OR goes to PCM pin 47 and the instrument cluster; 2-OR 8 volts from the PCM; 3- BK/LB goes to the engine speed sensor. (Note: the 93 does NOT have an engine speed sensor, just a crankshaft possition sensor)

How can I get the speedometer to work? Anybody has done a 47RH/NP241 swap in his/her 1st gen?
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Last edited by ClassA4x4; 11-14-2010 at 06:51 AM.
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Old 11-13-2010, 08:22 PM   #2 (permalink)
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I may not be understanding the problem because the solution seems a little too obvious. Use the voltage input and the return to the pcm and ignore the third wire.

Ie, connect the OR from the 95 speed sensor to the WT/OR on the 93 truck harness and the blk/lb on the sensor to the blk/lb on the 93 truck harness. Don't connect the wt/or on the sensor to anything.

Steve g
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Old 11-14-2010, 06:26 AM   #3 (permalink)
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Originally Posted by Steve g View Post
I may not be understanding the problem because the solution seems a little too obvious. Use the voltage input and the return to the pcm and ignore the third wire.

Ie, connect the OR from the 95 speed sensor to the WT/OR on the 93 truck harness and the blk/lb on the sensor to the blk/lb on the 93 truck harness. Don't connect the wt/or on the sensor to anything.

Steve g
I'll try that. It should work. It turns out that the BLK/LB in the 95 speed sensor is also the common sensor return. I was quick to favor the WT/OR since it connected to the instrument cluster in the 95.

EDIT: I tried it just now (easy thing to do) and it did not work. I tried the other way too, connect the wt/or of the NP241 to the BL/BK of the NP205 - did not work. There is a speed pickup contraption attached to the NP205 and onto which the 2-wire plug is attached, perhaps I need to put that thing on the NP241 - but i don't think it will it bolt on?
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Old 11-14-2010, 08:54 PM   #4 (permalink)
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I've been studying the wiring diagrams of both 93 and 95 trucks (I have both FSMs) and based on what I gleaned I will try the following tomorrow;

Sensor OR wire: 8 Volts from 93 PCM (WT/OR of old NP205 connector)
Sensor WT/OR wire: Pin 47 from 93 PCM
Sensor BL/BK wire: Sensor ground from 93 PCM (connected to chassis ground)

That means I'll have to run two new wires: 1 to PCM pin 47 and another to Ground.
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Old 11-14-2010, 10:13 PM   #5 (permalink)
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Quote:
Originally Posted by ClassA4x4 View Post
I've been studying the wiring diagrams of both 93 and 95 trucks (I have both FSMs) and based on what I gleaned I will try the following tomorrow;

Sensor OR wire: 8 Volts from 93 PCM (WT/OR of old NP205 connector)
Sensor WT/OR wire: Pin 47 from 93 PCM
Sensor BL/BK wire: Sensor ground from 93 PCM (connected to chassis ground)

That means I'll have to run two new wires: 1 to PCM pin 47 and another to Ground.
Maybe give us a little more information. What vehicle are we going into? Your current plan doesn't make sense to me. If the vehicle originally had a working speedometer with just a voltage in and a signal return, why would you now need to connect a third wire to a previously unused pin?

Take your old 2 wire sensor and hook it up. Spin the sensor with a cordless drill(correct direction) and ensure the speedo is working. If all is working, the simplest thing is to install the two wire sensor into the newer transfer case. The pcm and the dash don't care what spins the sensor. So why would changing the source of the "spin" require an additional wire?

So if it works with the old sensor and you can't mount the two wire onto the new case (I can't see why you can't. It uses a simple speedo cable style connection to mount it to the adapter) you need to find out why the newer sensor is not sending an appropriate signal. It masy be a different calibration and may not be compatible with the older pcm. I don't know, just throwing that out as a possiblity.

But check the speedo op with the old 2 wire first and get back to us.

Steve g
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Old 11-15-2010, 08:57 AM   #6 (permalink)
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The 47RH/NP241 from a 1995 trruck is being swapped into a 1993 truck that used to have a A518/NP205. There are differences between the PCMs in the two trucks, besides the NP205 and NP241 differences.
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Old 11-15-2010, 10:13 AM   #7 (permalink)
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The 47RH/NP241 from a 1995 trruck is being swapped into a 1993 truck that used to have a A518/NP205. There are differences between the PCMs in the two trucks, besides the NP205 and NP241 differences.
You don't care about the pcm in the donor truck, you are not using that chassis's electronics. It doesn't matter to the pcm what mechanicals you're using. The pcm in the 93 still only needs inputs from all the sensors it used with the old engine and doesn't care about what the 95 pcm needed. Same with the transfer case. It's not the 241 transfer case that needs a 3 wire speed sensor, it's the 95 pcm and 95 body electronics (which you aren't using either of) that needs the 3 wire. Unless you've changed the axle ratios you want to use the speedo pinion and sensor from the 241.

This is actually pretty simple. Use all the input sensors from the old engine and transfer case. Ignore any additional sensors used on the 95. This is a plug in swap. The only plug you will need to deal with is the 2 wire into the 518 changing to the 3 wire 47. 2 of those wires are common and the 3rd you are going to have to fabricate a control for the converter lockup.

Steve g


Edit, I meant to say you want to use the pinion (speedo driven gear) and sensor from the 205
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Last edited by Steve g; 11-15-2010 at 10:28 AM.
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Old 11-15-2010, 07:16 PM   #8 (permalink)
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Got it working

The speedometer is working now. Here's how I connected the 3-wire NP241 speed sensor:

BK/LB - PCM Sensor Ground (or chassis ground)
OR - PCM pin 7, 8 Volts output
WT/OR - PCM pin 47, Vehicle Speed Sensor pickup

I had previously assumed from reading the wiring diagrams that the WT/OR wire in the old 2-wire connector in the 1993 truck is at 8 volts; it was only reading 4.88 volts. The old 2-wire connector works fine for the NP205 speed sensor. Once I supplied a full 8 volts to the NP241 sensor, the speedometer worked!!!

I did not use any of the wires on the old NP205 connector.
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Old 11-15-2010, 08:12 PM   #9 (permalink)
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Quote:
Originally Posted by ClassA4x4 View Post
The speedometer is working now. Here's how I connected the 3-wire NP241 speed sensor:

BK/LB - PCM Sensor Ground (or chassis ground)
OR - PCM pin 7, 8 Volts output
WT/OR - PCM pin 47, Vehicle Speed Sensor pickup

I had previously assumed from reading the wiring diagrams that the WT/OR wire in the old 2-wire connector in the 1993 truck is at 8 volts; it was only reading 4.88 volts. The old 2-wire connector works fine for the NP205 speed sensor. Once I supplied a full 8 volts to the NP241 sensor, the speedometer worked!!!

I did not use any of the wires on the old NP205 connector.
I still don't understand why you wouldn't have just used the old speed snesor off the 205 and simply plugged it into the harness, exactly as it was before.
Steve g
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Old 11-15-2010, 10:04 PM   #10 (permalink)
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I still don't understand why you wouldn't have just used the old speed snesor off the 205 and simply plugged it into the harness, exactly as it was before.
Steve g
I would have done that in a hearbeat if the NP205 sensor fits in the NP241 hole. The two sensors are so much different in size and design.
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Old 02-21-2011, 11:46 PM   #11 (permalink)
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i have a 93 4x4 with a 5 spd what would be involved in putting a 95 auto in it
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