First, here is the 11 x 17 wiring diagram from the 1988 manual I provided in post 23 (Electrical schematic on 80's Rambler
That is how GM built your chassis. Coach mfg may make some changes but normally it will be 98% accurate. As shown in my previous hand drawing, the coach mfg added a diode isolator and AUX start solenoid. They should be integrated into the GM drawing in the manner I showed in my hand drawing.
Note: I have 1986 and 1987 GM drawings however they are difficult to read for someone not accustomed to that style of drawing.
Now referencing that drawing (Use bottom version ignition switch, not upper P42 Driveaway version):
1. Red (12g) I assume is always hot. Pin 2; goes to Magnetic switch
2. Brown (12g) is coming from alt/voltage regulator. Not sure if it's a direct path or if it goes somewhere in between the 2. Pin 4; 12 gauge brown (CKT 4) goes to fuse box. Smaller gauge brown (CKT 130) I believe goes to alternator.
3. Pink (12g) goes? Pin 3: Goes to fuse box
4. Yellow (12g) ignition wire goes to aux switch while joined with a blue wire (inline with wire, no switch needed to carry electricity) Pin 5 (forget AUX switch, thats the incorrect rewire causing this mess); Goes to Neutral Safety switch
5. Black (12g) is ground. Pin 150
6. Then I have a smaller gage that is red with white stripe. Not sure. May have been added by Coach mfg.
Age, heat, and add on's by an unknowing owner have a way of causing a fusible link to fail. Have had to replace a few on older MH's and cars. While an unloaded connection will reflect full voltage most people are testing the circuit in use which reflects the increased voltage drop because current is flowing.