K-Series Swap 88-89 Speedometer Connection

88-89 Preludes have a differential driven spinning cable (drive cable) that runs from the transmission into the back of the cluster. This turns the odometer and also creates an electric pulse. The electric pulse is used by the speedometer and ECU as the speed reading.

On H/B-series swaps it's possible to fit the 88-89 "speed sensor" (speedometer drive) into the H or B transmission and re-use the OE components like that... easy.

Unfortunately K-series transmission cases don't have the clearance required to fit the original speed sensor.

The solution is to switch to a 88-91 EF Civic speedometer drive. It has a smaller body because it lacks the integrated fluid pump that the Prelude one has.

Left is the RSX speed sensor, center is EF, and right is 88-89 Prelude:

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The EF Civic hold down plate is too long and the bolt hole too small:

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Shave the length down and drill the hole to 8mm:

As for the drive cable the Prelude one will work however it is much longer than needed. You would need to loop it around near the firewall and then run it into the speedo drive. Pretty "unclean" looking.

The solution for a cleaner look is to use a RHD EF Civic drive cable. It is much shorter:

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It fits into the Prelude cluster and takes a short route to the speedo drive:

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The EF firewall grommet won't work on the Prelude firewall so just take the one off the Prelude drive cable.

A LHD EF Civic drive cable should work fine as well, it will be a bit longer though.

The power steering lines that went to your original Prelude speedo drive need to be looped (not capped!). This will reduce the power assist you get at speeds under 20mph. However, it still has plenty of assist for a daily driver.

More info about the power steering stuff will be in the instructions for the Volvo electric power steering conversion bracket.