I'm wanting to wire up a set of foglights on my Blazer. I would like them to just come on with the lowbeams, and turn off with the high beams. Also have a switch on the inside to turn them on or off, so they arean't always on with the lowbeams.

Can someone explain to me all the parts I will nead, and how to wire it all up, please?

 

With a relay this can be easily accomplished.

You will could use a switch to control the ground to the relay, the lowbeam to be the +12v remote turn-on lead for the relay, then run a +12v hot. Then wire up the +12v to the fog lights. With this setup, you will only run a ground wire into the vehicle. So for the relay - terminal 85 goes to the switch inside the cab for the ground, terminal 86 gets the +12v remote turn-on lead from the lowbeam circuit, terminal 87 goes to the +12v on the fog lights, and terminal 30 goes to the battery or a switched source (but the battery is fine because the relay will not be energized unless it has both ground and +12v input on terminal 86) and this should be fused as well.

Now you could also only run it off of the lowbeam 12v source if you can find the wire in the dash. Then splice into that wire, thru a switch, and out to the relay. In this setup, terminal 85 would be simply grounded, terminal 86 gets the +12v remote turn-on lead sourced from the lowbeam and switched inside the cab, terminal 87 goes to the +12v wire on the fog lights, and terminal 30 gets fused and connected to the + post of the battery.

Either way works. Here's some information on relays: Car Audio Electrical Components - Cont.

Let me know if you need anything else.