Ok, I finished doing the wiring harness (12 circuit painless) in my truck, and I've ran into a few problems. I think i've got it down to the turn signal switch, but I just want to make sure.

First, w/ headlight switch in off position, when I hit the brakes, the dash lights come on, but brake lights don't. Turn signals do not work either.

Second, w/ headlight switch pulled out halfway, left parking lights come on (including left rear), and dash lights come on. The turn signal dash light also comes on, and dims when turn signal lever is down, but doesn't dim when lever is up, or off.

Third, w/ headlight switch pulled alll the way out, parking lights go off, turn signal dash light stays on, high beams go on, and high beam indicator light goes on. Brake lights still don't work, and nothing dims.

Also, the horn will unexpectedly blow sometimes, but very quickly.

So I have no low beams, no brake lights, no parking lights on the left side, no turn signals, and i'm prolly forgetting something.

So is it the turn signal switch? Dimmer switch? combination of both? or am I missing something?

Sorry for the long read, and thanks for the help in advance.

first thing to check for p[roblems like this is lack of good grounds// did youi make sure all your ground wires were shiney metal to shiney metal not paint on paint

Make sure the 4 way flasher switch is in the off position and see if there is a difference with what lights up and not light up.........

no 4-way flasher, and grounds are good/new. As far as grounds go, how many are there?
There's of course the one from the battery to the alternator braket. One from engine to frame. One from frame to body, and there is a dash ground. Also a sending unit ground. like I said, the wiring harness/fuse box is brand new.

ground core support to frame ground the box to the frame gronnd the firewall to the engine(2)
can never have too many too clean grounds to make electrical system work properly
headlight pigtails grounded ??bare metal on bare metal ??parking light pigtails grounded bare metal on bare metal?? horn mounts grounded bare metal on bare metal??
BAD GROUNDS=BAD ELECTRICAL SYSTEM
do yourself a favor get a sheet of 80 or 100 grit sandpaper and anywhere a black wire is attached clean to bright metal and reattach the wire

I helped another board member down here in austin with a painless harness...the headlight switch connector had two of the wires crossed..he had similiar issues to what you are stating. Do you have the original harness to compare it too?
Another item to check is your steering column connections/turn signal switch assembly...may have some problems there if the horn is going off unexpectedly.

yes, I have the original. The thing is, since my truck is a GMC, I had to wire in two more connectors for the two other headlights. I'm pretty sure I followed the directions painless provided.

I'll compare the two tommorow.