wrx

I know very little about cars so talk slowly It's got a PPP ECU if that makes a difference.

greasemonkey

Doesn't it come with instructions?

Doesn't make any difference whether it's a PPP or not, wiring is the same. Basic connection is simple, negative goes to earth connector on battery (unless you have additional earths fitted), +12v to a switched positive (stereo power supply for example) and lambda input to lambda wire on ECU loom (which is pin 21 on connector B136), or blue plug, third row down, third wire in from the right as you look at the wiring side of the connector).

wrx

Thanks it was the sensor wire I was having trouble with.

greasemonkey

Some will tell you that you can get away with scotchblocks and piggy back clips to make that connection, personally, I don't think this is good enough.

The lambda wire carries very small voltages (the difference between rich and lean is less than 0.2 volts, and thus the quality of this connection is vital to an accurate reading. Best approach is to remove the insulation from a secton of the wire running into the ECU connector, and solder your AFR meter's wire into it. Wrap it with insulating or self-amalgamating tape when you're done.