Testing circuits

yep provided your updated car followed some semblance of sanity i.e what you put back may differ from what you take out..BUT the saving grace is, its all the same kit you are connecting up

but unless Mr hackit about has been in there... it will be poor connections first and foremost... can of de-oxit and some needle nose pliers and you could be well on your way

in mine i cut off the last 5-8 inches of any suspect wire got a length of the right colour crimped on a nice new connector with appropriate insulating jacket or plastic connector, plugged it into the device and then ran it back with enough slack to join with the loom.
slid some heat shrink tube a long way along and solder

i solder my connections doing a poor interpretation of the "line Mans" splice and cover with heat shrink when cool.

i say poor interpretation because a lineman's splice is only really appropriate for solid core cable. its a physical connection which is hard to pull apart. and i make it harder by glueing it with solder....

many will say this is not the right way.... but it works and has worked for many years for me..
and if you ever do unwrap the whole loom of a chrysler. you will find the factory were happy to do the same thing, mid cable run, under the wrap, where it could not be seen. end of one spool of wire connected to the next... no wastage in the wiring loom shop :) at least in Australia there wasn't. a soldered physical connection in a supported loom with little flex is not going to fatigue....

word of warning what was put in originally is often a better quality connector than what you can find today. choose replacements wisely, the silver stuff with blue plastic insulator from Halfords works but is really quite rubbish.

Dave