If an AEM system was previously installed, that suggests the car was/is modified.
If you could give us a run down on what mods the car has at this time, (and what your goals for the car are) it would help us give you accurate advice on a good, cost effective path forward.
As far as returning the wiring to "stock", best thing you can do is post a few pics of what you got to work with.
Generally, when people pull an aftermarket/modified ecu out of these cars, they take some of the sensors/gauges/ other toys out and leave a mess behind
... it may be just be "untidy", and a little work can bring things up to snuff.
If things aren't completely fubar
, individual pins as well as the connector shells are available.
With some time and effort, you can piece things back together quite satisfactorily.
... and it may also be that things are hashed enough that a "plug~n~play" ecu ... won't plug and play ... even after you rework the ecu / connector side of things, other sins of the hackster out in the engine bay may prevent things from working properly.
Good news is that you're located in the PNW, and there is some damn
saavy board members up there that will help you sort things out. helpfull hint, they like alcoholic beverages