I bought a PSI Powerbox off eBay for my Marea 2.4TD, however I can't work out where it plugs in.

Anyone got one of these?

I've never seen a power box for the 2.4td advertised before. Are you sure it's not one for the JTD? PSI as far as I know have jumped on the 'common rail performance box' bandwagon and don't touch any of the more conventional diesel fuel systems

If it is the correct box for your rotary fuel pump then I had a similar unit fitted to a Freelander once - had to splice and solder it into the ECU harness. For common applications, they have connections that allow you to plug inline between the ECU and the fuel pump.

Yes, it's got two round connectors a bit bigger than an inch in diameter so that it can be plugged in inline somewhere.

I think you're correct that it plugs in between the ECU and the injection pump, however I can't find the ECU.

Where has Fiat hidden it? - I've looked everywhere for it.

They normally plug in at the fuel pump end. Is there a part number on the unit to establish if it's the right box for the 125TD?

The box says PB200007/b or PB200007/6 (not sure if it's a 6 or a b)
Then 12990.

The connectors are round with seven pins inside. The male connector is about an inch in diameter.

I found a few websites which list the PB200007 for a BMW 2.5TD engine. However I also found this one which lists it for the Marea as well...
http://www.egmo.ch/sites_de/tuning/dieselpower.htm

Looks like this box works with a certain type of Bosch IP.