slight miss after tune up?

this is a 2 part question please.

1989 2500 scottdale 350 fuel injected.

first one is while doing a tune up i found a single purple wire with a female connector pin directly behind the distributor unhooked. it is not the advance timing wire because i have found it. i am thinking maybe a test lead for something?

second question

did a tune up on this truck. wires, plugs distibutor cap and button. now it has a slight miss i can only notice while at a light or sign when in drive and the brake on. not a constant miss or hard just a intermittant hessitation miss. why would this come about only after the tune up?. i have trace all plugs for cracks and there is none.

Could be a few things. First off, what type of plugs did you put in? From experience I have learned that AC Delco plugs work the best on many GM motors. I've probably tried every brand except Splitfire, I knew better than to ever attempt those. Anyways, I'm not sure if your '89 calls for platinum tip plugs or not, if it does then AC Delco's platinum tips work the best. In any case, if your motor calls for platinum tips, be sure some kind of platinum tip gets put back in.
Other suggestion would be double check your vacuum lines. Maybe you popped one loose while doing the tune up. Also would make sure all plug wires popped into place.
Whatever is causing your miss, sounds like its something small and minor to fix. Check the easiest stuff first.

Could be a few things. First off, what type of plugs did you put in? From experience I have learned that AC Delco plugs work the best on many GM motors. I've probably tried every brand except Splitfire, I knew better than to ever attempt those. Anyways, I'm not sure if your '89 calls for platinum tip plugs or not, if it does then AC Delco's platinum tips work the best. In any case, if your motor calls for platinum tips, be sure some kind of platinum tip gets put back in.
Other suggestion would be double check your vacuum lines. Maybe you popped one loose while doing the tune up. Also would make sure all plug wires popped into place.
Whatever is causing your miss, sounds like its something small and minor to fix. Check the easiest stuff first.

yes i used ac platinum plugs.. gapped at 35.

anyone have any info on this purple wire behind distributor single female connector?

The miss could easily be caused by your moving the spark plug wires around during the tune-up. That is, if you now have a couple of wires that are too close together, they could be arcing or crossfiring. I would try seperating the wires as much as possible and then see what happens. Also, be sure you didn't knock a vacuum line off somewhere.

I had the same problem...turns out it was a plug wire on the manifold arcing!

Check the resistance of the wires to make sure one doesn't have a broken conductor.