The LSO pins are standard TTL, so 3.3v-5V and probably 50mA.
There are multiple routes to go. Only direct connect to another TTL device.
You will need to make a small circuit with a resistor, a diode, and transistor as an input from the CPU LSO.
Then your external relay is switched on from the transistor. The transistor is switched on from the LSO.
You are going to need to know how many Amps the electric fan draws. Say it is on a 20Amp fuse. You could then get a 5v TTL coil driven high current relay that supports 12v/25Amps. Then you won't need extra components, just drive the relay directly if it is TTL. These exist in the Arduino world.
I think the easiest, is to wire the CPU pin from the board, to the spare 60pin pin on the circuit board, just a straight wire, then that is done, and less chance of screwing something else up on the board. Of course you could use say pin #34 on the 60-pin connector, follow its trace, you will notice it goes to a blank missing component with 14? or 16? pins. This is for Data Output Link(DOL or TripMinder), and the chip drives PWM to the TripMinder from the CPU.
What I am saying, is you could run a smaller wire from LSO CPU pin, that missing chip area, then solder in components to drive Pin#34. Then your 60pin under the hood is a 5V on/off ready to go.
I am planning on using DOL, pin#34 as I have a TripMinder from a 92ish TBird that I'm putting in my dash.
Next wire up the pin on the 60pin connector to your relay, or your custom TTL relay driver.
This is just off the top of my head.
I will be doing similar soon, I have a VGT that I am planning on hooking up, but using HSO.
What about the ac wot cut output? Your still using the thermactor smog pump? You could even use the mil output if you wanted.
why would you want to use something like that? Seems like an aweful lot extra to shove inside the ecu case. Ideally you want the relays outside the ecu that way your not running a power feed wire inside the ecu.