Welcome to the board.
Here is the RENIX manual with explanations and diagnostics.
http://pirate4x4.com/tech/billavista/PDFs/Jeep_Renix_Fuel_Injection_manual.pdf
And a wiring diagram, it's for an '88 but is probably 90% identical.
http://www.comancheclub.com/forums/viewtopic.php?f=9&t=12734
Almost as exciting as the 2006 NHRA Top Feul finals when another "Tony S." had to win the finals and set a national record to win the championship. I was on the edge of my seat for both.
I've seen caps that look similar to the originals (black with orange lettering) at O'Reilly Auto Parts. I'll get one tomorrow and let you know if it fits. Looks lik this.
http://m.summitracing.com/parts/RNB-82594
They seemed to be on there pretty good, I couldn't just pull them off with my fingers. My stock ones did not have them either.
I attached the thread (with pics) I was talking about, and precision responded eventually.
The ones you receive from precision will probably have blue tips and look more like a beanie, that's a stock photo. I asked this same question to precision (and on this board) and was told to leave them on. The rebuilt injectors come with new o-rings.
http://comancheclub.com/forums/viewtopic.php?f=2&t=31399