Two different temperature sensors... why?
 

The parts Katalog lists 2 part numbers for the coolant temperature sensor - 996 606 410 00 which has 2 pins and 996 606 405 01 which has 4 pins. Anyone know what the difference is?
The 2000 3.2 replacement engine that I bought had a broken connector (2 pins) but the original engine, which is the same year, same model (2000 M21) has 4 pins. I was going to switch the sensors but the connector on the wiring harness won't fit. Guess I'll buy a new sensor, but is there a reason for the different number of pins?

No idea what the difference is, but why not just swap over the sensor from the original engine? It’s almost certainly a thermistor of some sort, lifetime is probably somewhere in the millions of heat cycles…

That was my intention, but the sensor from the original engine is 4-pin and the wiring harness connector on the replacement engine is 2-pin. I don't want to hack the wiring harness... and a new connector will likely cost as much as a 2-pin sensor ($15 for a non Porsche replacement). I'm just wondering if there is a important difference between the 2 parts.

look up a wiring schematic and trace the wiring of both types out.
That should give you an idea of the differences.

You want to make me work for an answer??!! ;)

Good idea though...

Sometimes you have to put forth a little effort:)
A good schematic should show you whats what.
Being a German system figuring out some of the symbols and notations can be a pain at times though.
Let us know what you find;)

I understand parts of the 928 wiring diagram... so I have a good start.
So from what I can see on the wiring diagram that I have for the Boxster is that the 4-pin connector is for 2000 and the 2-pin is for 2001, which is coincidently what my engines are... a 2000 and a 2001. I didn't follow all the connections, but there seem to be 2 sensors on the 2001 engine, the "temperature sensor engine" and "NTC water compartment" sensor, each with 2 connections. They are side by side on the wiring diagram. For the 2000 engine there is a single "double NTC cooling water motor temp" sensor with 4 connections.
Changing the connector on the wiring harness would likely not work. I hope that the ECU knows how to handle this, I will assume that it sees the 4 lines coming in as the same thing whether they come from one 4-pin connector or two 2-pin connectors.
Therefore, install the connector that fits the wiring harness on the engine. (duh... sometimes my brilliance blinds me :)

I assume you are using the harness and computer from the 3.2? Is that correct?

Comment removed. Incorrect info

In the 4 pin sensor, it appears that is the one used when the instrument cluster contains a coolant temp gauge. The Blue/red wires are used for the cluster signal (blue/red signal brown/orange is the analog ground). The brown/pink wire and the blue/white wires are the sending circuit for the engine computer. The 4 wire is what is called "double NTC cooling water motor temp”. The other 2 wires are on the instrument cluster diagram but they are in the same connector. Very confusing. The engine temp sensor is the engine compartment temp sensor mounted on the intake between the front 2 passenger side runners. Hope this helps.