so ive just mounted an ej25 into my 74 baywindow and i need help with the wiring loom , what do i do first with it? is there adaptors i need to purchase ...? where should i mount the ecu?

AM automotive are the Subaru wiring gur's and can set your loom up. Cost far out ways the hassle of going through it all on your own

http://amauto.com.au 

If you have the orig harness from donor front cut or car , i would hook it all up make sure the engine starts and slowly remove excess wires and modify it all the while making sure that nothing you've removed has affected its operation

I sent my complete loom for the EJ20 in the Manx SR to Brad at Custom Off Road.

He returned it reduced to the essentials with every wire labeled.

That made it very easy for me, a compleat idiot and a newbie at computer controlled engines to set it up as a completely trouble free instalation for the past 4 years.

He charged me $400 plus GST in 2006. I consider that money well spent.

After I'd removed the tape from the loom I had a huge mess of what could only be described as technicolour spaghetti. I had no idea where to start or what to do.

Brad solved the problem and made the rest easy.

See http://www.customoffroad.com.au 

I put the ECU in a double insulated water proof electrical control box and attached a 12 volt computer cooling fan with a remote inlet, which is always running when the ignition is on.

I mounted it in the engine bay beside the engine. It has never given any indication that it is too hot on even the hottest days. Even in traffic jams when the engine cooling fans are running nonstop.

Mount it as far from the engine as you can, insulate and cool it if needed.