Hello. I ordered a heated oxygen sensor for my 90 Formula 5 speed. I need to hook it to a power source. The car does not have smog anymore so the seller told me to hook it up to the egr wire. I want the install to be reliable and clean without butchering any wiring. Thanks for any help, pictures are a plus.

You can tap onto the fuel pump power wire. It need to be a accessory powered wire.

So your not hacking the wiring you can crimp on a new terminal .
https://www.eficonnection.com/home/p...relay-terminal
You will have to check the wire gauge or ask efi connection

There isn't an accessory terminal in the fusebox? Switched on with ignition, wouldn't have to be on during cranking.

If the fusebox is in the passenger compartment, route the wire out the firewall, be sure to seal the hole (or run it out an existing hole,) Assure that the wire can't chafe on the sharp sheetmetal edge of the hole (a grommet helps.)

Even if there isn't an open accessory terminal you can use, there are various styles of power tap that can allow you to sneak a wire to power without making a career out of it, or causing permanent damage. An ATO-ATC power tap could do the job and be removable later, leaving no trace.

Both the EGR and the Air solenoids have keyed 12 volt power supplies. Either would work. Realistically any of the engine harness wires that are Pink with a Black stripe are keyed fused power supplies.

Yes use Egr solenoid pink/blk wire. Thats the best place and most accessible area for doing this.