Mazda 323 system checker substitute

Have a 1986 Mazda 323 fuel injected that if it did have an "engine light" it'd probably now be on.
But it doesn't have one. Stores I've checked so far have no code reader. Somewhere on the 'net recently I saw a how-to for using just a jumper wire to initiate the system's outputing of the codes & an LED light or meter to watch for the actual code output.
Anyone know which pins have what signals & which pin to give a voltage or a ground potential in order to get the code output?
tx

PS I've already found the meaning of the codes.

How did you get on? I have an 87 efi 1600 that won't start but has fuel and spark so would be keen to read the codes if there are any.

Cheers
Matt.