I fitted a led/light to my mondeo so I knew when the engine was doing a regen. I've done this guide so if people wanna do the same thing hopefully this will help them.
I fitted my led near my instrument panel.
I started off by running a wire from the light which will sit near the instrument cluster and I run the wire down behind the small compartment on the drivers side.

Next a ran the wire under the dash on the drivers side.

Then I used a welding rod to feed the wire through the dash/centre console.

Then I fed the wire/welding rod through the gromit in the bulk head. You have to remove the glove box to see the gromit narrowed.

Next up go to the fuse box in the engine bay and find the relay,circled.

Next find the right pin on the relay to solder one of the wires for your led to.

Use pin 5 as in pic.
Then wire one of the wires for your led to an earth point. I used the the earth point near the battery ,circled, but I suppose you could earth the wire out any where on the body.

I used a 3mm led bulb and sat it between the instrument panel and dash. And as you can see the led lights up when the engine is doing a regen.