I worked out that the water heaters that were used in the Transit Connect van happen to be the same Mitsubishi unit that are used in the i-MiEV.
The unit is labelled Mitsubishi CKA411A001
Below are the schematics and photos of both.
There are 4 x PTC heaters controlled by 4 x input connections. Presumably these are 12 volt.
There are also 2 temp. sensors. One on the water input and one on the output of the heater block.
This may all be academic as the heater unit weighs a ton and I want something lighter like these MES units from Metric Mind