2 wire VSS to 3 wire VSS conversion questions/help

[dankberries]

I'm looking for some guidance in swapping my VSS from a 2 wire sensor to a 3 wire sensor.

The car is a 1998 impreza L originally equipped with a 2 wire VSS. The speedometer isn't working and I've narrowed it down to an issue likely with the motor that moves the needle in the cluster.

I couldn't find any info on fixing the cluster, I've read that the 1998 year was problematic with this. This has prompted me to swap the cluster with a newer style(MY99-01) that utilized the 3 wire VSS and a change in the style of connectors.

The cluster swap is easy and moving the wires around to there correct location is not a problem.
I'm struggling to understand the wiring for the VSS. From what I've read it's apparent that the signal is output differently between the two different VSS sensors. The car is an automatic transmission so the TCU will need to see a signal in addition to the cluster and ECU.

My question is, will the TCU interpret the signal correctly with the different sensor? What is my approach for wiring this in?
When I dig into the FSM, assuming it's accurate for the 1998 impreza L , it appears the signal leaves the sensor and goes to the TCU, then leaves the TCU and splits to the cluster and ECU.
Is at as simple as using the the original signal wire and moving into the 3 wire VSS signal pin? The other two pins on the VSS are for ground and switched power.

I could intirely be over thinking this all as I do that alot. I've seen a few other forum threads but none that specifically mention using an automatic transmission.

Sorry and thanks in advance. I know this isn't legacy specific but the knowledge base here is strong.

[dankberries]

I believe this diagram to show the configuration for the 99-01 wiring.

I've wired the signal from 3 wire VSS directly to the ECU and gauge cluster. I'm not getting a reading on the speedometer and the diagnostic isn't picking up a reading. I figured even if I don't have an answer for the TCU that wiring directly to the cluster would at least give me a reading.

I am using an unknown condition VSS, I'll buy a new one and try again.

[dankberries]

1998 combination meter



1998 wiring schematic for VSS

[dankberries]

MY99-01 schematic




MY99-01 Combination meter

[dankberries]

Update:

I replaced the VSS with a new unit and now the speedometer and diagnostics are reading.

I'm only able to move the car in my driveway and haven't gone more than a few feet and 5mph. I'll have to wait for better weather.

I'm still uncertain on TCU interpretation, I'm guessing because I only tied the signal to the cluster and ECU I'll likely throw a code with more driving. If that's the case I'll tie the signal to the TCU , however I think the 2 wire sensor put out a wave form signal and the 3 wire is not the same. I'm questioning the ability of the TCU to interpret the signal of a 3 wire VSS.

[Legacy777]

You should just have to tie the signal wire from the 3-wire into the VSS signal wire on the 98. If you do that in the engine bay the TCU should get the signal. The VSS just outputs an on/off signal that the ECU & TCU interpret as speed.

When you get a chance to drive it let us know what it does.

[dankberries]

Thanks for the response Josh. I've been able to put some miles on the car and have had no codes or transmission related issues.