I did this over the winter with my '66. I am very picky and did it without cutting into my original wiring (diagram will tell you differently). If your are interested in this method or have specific questions just PM me.
If you do a search, you will find some quick notes I wrote up about what you need to do. You don't have to cut your harness at all if you have the correct harness. There's a step that talks about hooking up the rear tail lights so they come on with the fog lights. That step "might" require you to cut but the rest shouldn't. Depends on the harness you have in there. I didn't have to drill a hole either, there was one already there
If you do a search, you will find some quick notes I wrote up about what you need to do. You don't have to cut your harness at all if you have the correct harness. There's a step that talks about hooking up the rear tail lights so they come on with the fog lights. That step "might" require you to cut but the rest shouldn't. Depends on the harness you have in there. I didn't have to drill a hole either, there was one already there
This is true about having the rear lights come on when the fog lights do (factory style). You can still do this without cutting into any factory wiring by wiring directly to the positive side of the solenoid or pluging into the positive side of the ammeter for your power source (although you will loose the ammeter, but not a big loss and you can still plug it in later if you want).