I have abandoned the stock guages, and replaced them with the Autometer Tach and Speedo. I know what to do with most of the wires that went to the plug that went into the back of the stock guage housing, except for 3. There was a double pink, which according to the wiring diagram, one went to the backup light switch and the other to the ignition switch, however they both merged into the plug. What do I do with them? Connect them together? I've tried all different combinations of having the ignition switch on, and checking for continuity from where they entered the plug, etc. Also, there was a double green wire which was used for one of the senders, which I have used one of the wires for my autometer guage sender, but again, what do you do with the other? I guess I don't understand how those circuits are wired. Why were there double wires?

Killer, when there are doubled wires, it is just an easy way to run multiple connections without splicing inside the harness. The dark green, for example, went from the bulkhead connector to the circuit board, then back to the ignition switch. This double is only found on a factory warning light car since it grounded the temperature lamp when the ignition switch was turned on, showing that the bulb worked.
The pink is a similar situation, it doubled at the circ bd connector to feed 12V ignition to the idiot lamps and fuel gauge, then went down to the back-up switch and supplied 12V ignition.
Hope this helps!
tech@factoryfit.com

That makes sense. So in my situation, I cap off the green right? If I keep both pink connected, how are the backup lights going to get power?