20 years ago at a MACS convention. He passed out tiny crayon boxes and schematics for the techs to actually learn by doing. I ran into a few during the class break who expressed disinterest in 'coloring' at their age. I'm 57 and I LOVE to color - with crayons with my granddaughters AND highlighters on complex schematic print outs. I like to keep my colors consistent and make a 'color coding key' on my schematic print out. I use an orange highlighter for B+, pink for switched ignition, leaving green for ground along with blue and yellow as 'wild cards' for other circuits I encounter. For example, I often highlight serial data with yellow and use blue for 5-volt sensor supplies. Figure 3: The tools needed for understanding complex schematics are a set of colored highlighters and a magnifying glass. In figure 5's 'inventory of components' there are 2 high wattage resistors within the fan motor assembly. The motor gets voltage direct (no voltage drop), through one resistor or through both resistors depending on which relay is turned on. It might also be helpful to divide the circuit in sections like I did - one half of the page appears be related to controlling a pair of relays in a separate relay center along with ground bus bars. The other side of the page contains the three speed control relays so I marked one side "Speed" and the other side "Control" to help me determine the logic of ing / highlighting components and circuits you can see. Print out the schematic page(s) so you can use multiple colors of highlighters (Figure 3) to trace key circuits that are relevant to your diagnostic goal. In this case it was to determine why the cooling fan motor might not run and why the starter solenoid doesn't seem to activate at times. Color coding wiring schematics has been a tactic used by diagnostic pros for many years. Jorge Menchu at AES Wave first brought it to my attention close to Figure 6: Step 2 - What are the P & G's? (Powers & Grounds) 1. Fuses F22 (10A), F7 (40A), and F6 (60A) 2. Grounds G102, G100 plus ECM grounds 3. Pin 30 supplied with non-switched 12V all relays EXCEPT Fan Speed Control 2 4. Both control relays & Hi Speed relay have ignition to pin 86 and switched grounds to pin 85. 5. Medium and low speed relays both have ignition to pin 85 and switched grounds to pin 86. December 2016 4 MACS Service Reports