Ford F-350 must be BLUE (around 20 AWG) right to the stearing column... as i remind in a black 5-8 pin connector, the last one right to the stearing column. Just remove the panel under the stearing and look at this. As i remind it's in the same connector as the cruise control too (if you have)

Under the dash you can acces also
1. 12V = Yellow or Green (sometimes green/black) (14-16 AWG)
2. Ignition = RED with GREEN tracer, (sometimes green/something)

Be careful when testing the horn wire, use multimeter or logic probe. AND it's a negative signal to activate the horn.

AmountOfPulses = GPIO & $0F ' Get only value of GP<3:0>

I assume that it reads those pins and stores the value in the variable. I need to know how it does that and how does it adjust from 0 to 16 pulses with only three switches.
with my circuit, you're using 4 switches. In binary, it gives you 16 possibility

DIP PULSES
0000 = 0
0001 = 1
0010 = 2
0011 = 3
0100 = 4
0101 = 5
0110 = 6
0111 = 7
1000 = 8
1001 = 9
1010 = 10
1011 = 11
1100 = 12
1101 = 13
1110 = 14
1111 = 15