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99-01 Super Duty Cluster Swap - Tach Correction Solution for 97-98 Vans

3K views 4 replies 2 participants last post by  Rammstein1224 
#1 ·
I decided to undertake the cluster swap in my '97 and in my research, it was made clear that the tachometer would read high and the scale would be off. Since the 99+ CTO signal operates within a range of 43-200Hz and the 94-97 CTO signal operates within 130-720Hz, some sort of modification is necessary. What wasn't clear in my research was how to properly fix it and the correction seemed to be a closely guarded secret on the forums for some reason.

I disassembled cluster, examined the PCB, and found the datasheet tach driver IC (CS4121). In following the calculations for the trim resistor, I learned that for us 97/98 owners, we must simply short (read: bypass) R19. The trim pot will then allow you to adjust your tachometer to the appropriate range.

I've read in several posts suggesting the installation of a 10k Ohm or 100k Ohm resistor inline with the CTO signal. This is unnecessary and if you have one installed, remove it.

As seen in the pictures below, I simply soldered a piece of wire across the resistor. Hope this helps you guys out! Now if only I could figure out how to reprogram the speedometer driver to correct my VSS signal ;) .

R19 Replacement:


Adjust this trim pot:


Swapped:


Idle:


1000:


1500:


2000:
 
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#2 ·
I should have done a proper How To thread...maybe one day. However, a couple points to note for the swap as well.

First, you'll need to use the clear cover and black carrier from your van cluster.

Secondly, mounting holes. The top right hole will align properly. The bottom two holes will be slightly misaligned, but should still work OK. You'll need to trim off the top left mounting tab from the SD cluster carrier (the white part).

Lastly, you'll need to trim a small part of the inner dashboard. It's hard to describe especially without pics, but before plugging everything together, test fit the newly assembled cluster and you'll see where it interferes.

Here's a quick and dirty breakdown for which pins go where. A couple signals need to be inverted. I don't care about the seat belt light and I don't have ABS, so I didn't have to do any inversion to make my indicator lamps work and I simply removed the bulbs.

I manually transferred this from my spreadsheet, so hopefully there are no errors.

Code:
16 Pin Connector   |   12 Pin Connector (White)   |   12 Pin Connector (Black)
-------------------|------------------------------|-------------------------
Pin 1 (Remove)     |                              |  
Pin 15 -->         |                              |  Pin 12
Pin 13 -->         |  Pin 11                      |
Pin 2 -> Pin 1     |                              |
CTO -> Pin 12      |                              |
-------------------|------------------------------|-------------------------
                   |                              |  Pin 1 (Remove)
                   |                              |  Pin 4 (Remove)
                   |                              |  Pin 2 -> Pin 1
                   |                              |  Pin 8 -> Pin 11 (Needs to be inverted)
                   |                              |  Pin 9 -> Pin 8
                   |  Pin 9                       |  <-- Pin 7 (Needs to be inverted)
-------------------|------------------------------|-------------------------
                   |  Pin 5 -> Pin 8              |
                   |  Pin 4 -->                   |  Pin 3
                   |                              |
16 Pin connector:


12 Pin Black Connector:


12 Pin White Connector:
[/QUOTE]
 
#3 ·
Just curious whats the reason for this? Is it just so you have a tach display because the vans dont?
 
#5 ·
Ahh i see, well good job man alot more knowledgeable than I with this kinda stuff
 
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