ACE LS Swap owners, have you ever wondered what's in that mysterious black box of electronics? Allow me to de-mystify.

First of all, the box was full of black RTV. I spent about 30 minutes chiseling away the silicone like a miniature archeological site. What I found next was a lot simpler than expected. I made a diagram.

TPS (Throttle Position Sensor)
The wires were simply connected together in the box. So, that implies that the Rover and GM TPS signals are compatible. It's probably a voltage range like 0-12v to signal how open the throttle is.

VSS (Vehicle Speed Sensor)
Here's my understanding so far:
This box converts the VSS signal from the LT230 transfer case to the GM ECU. The GM ECU needs this signal to run the engine properly. The Rover LT230 VSS is probably outputting a square wave from a reluctor wheel. But the GM ECU expects a pulse signal referenced to ground. This circuit is a simple "RC circuit" which acts as a high pass filter. Meaning it will let through high frequency changes in voltage, but eliminate any low frequency changes. So when the square wave rises or drops quickly, the filter outputs a positive or negative spike. When the square wave is flat, the filter output is 0v. Therefore this circuit converts the square wave into a series of pulses which the GM ECU can understand.

 

It was always destined to be simple. Someone just took the time with the right tools to make them talk to each other. It was never going to be elegant or super complex, it's just far over most folks heads.