Buick/Olds: Wiring for camper/trlr w/ elec brakes, brake light switch, fuse box

Question
Is there a preferred place to drill the hole?  Where under hood should i connect the 12v lead to the trlr-solenoid or battery? or is there a place on the fuse box in the car to run that from?-------------------------
Followup To
Question -
92 roadmaster wgon. 5.7L. bought it used & it was already set up for a flat4 plug. My camper has an 8 wire set up, mostly figured out. I took my trlr harness & spliced in a flat 4 for the lights. I ran a line through the interior for the elec brake line & took a feed off the Backup lts  so that is ready too. The big questions are:
1) Is there a 12V line in the left rear area that i am working in that i can feed to the trlr battery to charge as i tow? I noticed a purple line with a stripe that is heavier than most, could that be it?
2)I couldn't find a place in the firewall to run the leads for the brke control directly to the battery as they suggest. Where might it be, or is
there a heavy duty enough connection under the dash(and where)?
3)dont want to upset the ABS/cruise etc. Where would/should  i splice into to connect to the "cold side" of the stop light circut under the dash(line color & location)?
Answer -
1)There isn't a 12v power wire back there that you can use unless someone has all ready run one for the trailer.

2)There probably isn't a hole in the firewall to run the wires. You will have to drill a hole.

3)You should splice into the white wire off of the brake light switch. It is directly above the brake pedal.

Answer
You can drill a hole anywhere you want, just make sure that you dont drill into anything else. I usually try to drill through near the base of the steering column.
You should hook up the leads according to the instructions that came with the electric brake or trailer harness. I dont recomend hooking it up to the fuse box unless that is what the instructions tell you to do.