I agree that discoloration has nothing to do with the condition of the wires. Insulation do affect the condition of the wire. Since I am not getting spark on some plugs I wen't to ckeck the condition of the fuel injector wires. I did not get any shorts or partial short and ground to the positive side on any of these wire. When I turn on the ignition, I got 11.99 volts. So, I presumed the problem wasn't there. I never had any problem with the wiring harness before nor gives me indication that the harness is deteriorating. I did sprayed wd 40 on all injector wire sockets. I will try to spray a contact cleaner just to be sure. But, the voltages and resistance reading at the plugs give me a good reading and no intermittent readings.
94 E320 Silver 210000 miles
94 740il Pewter Green 97000 miles- Retired
05 S430 4Matic
07 Lexus IS250