Timing and trouble codes

[intimidatordei]

I have a 1994 S-10 with a 4.3 CMFI engine. I am looking for help with two problems.

1. I am trying to check my ignition timing but I am having trouble locating the tan with black stripe wire that must be disconnected in order to check the timing. If anyone can help me locate this wire, I would be greatly thankful.

2. This has to do with trouble code 45 oxygen sensor or circuit - rich exhaust detected. My "service engine soon" light comes on only when I drive on the highway at 65 - 70 mph for several miles. As I slow down to 45 mph the light goes off. Trouble code 45 comes up when I check the trouble codes. Does anyone know what would be causing this to happen?
The only mods to the engine are a high flow cat and muffler system.

Thanks for any help anyone can provide.