Getting Ready to Assemble My 1967 Mustang Fastback Project, Quick Question.....

It's never a bad idea to wash the parts before priming. No need for overnight soaking.

Simply wash them with soap, and then dry them off. I will use and old toothbrush to scrub things. Prime and paint. I often, more than not, will also wipe the parts with alcohol before priming. That is all you will need most of the time for good adhesion. If you want on car bodies you can also scuff the surface with something like 3000 grit paper, wash, dry and them prime if you really want to make sure.

Bk

Unless there's visible evidence of something like a mold release agent -- which has been pretty rare on most mainstream models for decades, now -- I will generally just give a good rub-down with alcohol and a lint-free cloth to make sure fingerprints and skin oils are gone. Soaking seems needless unless there's a specific issue.

Thanks guys for the info, I think I'm going to rinse the parts in light soap and water, then rinse, and dry. For the body, hood, trunk lid, and anything else body color, I'm going to use alcohol and follow with a tack cloth. Anyone else with suggestions please keep them coming !

A couple of years back I just went back to Odorless Mineral Spirits as my wipe down. Once dry I just blow everything off with the airbrush before I fill it with paint and shoot primer. But my primer is Stynylrez and when I used alcohol I noticed this funny looking motor oil in water look to the surface of the primer. It didn't do anything weird but I didn't like that so went with the MS.

Just an addition to the advice on scrubbing with a toothbrush:  I use a cheap electric toothbrush for scrubbing parts (use it for both washing and stripping paint).  Because of the tiny oscillations it makes for the scrubbing action, its not as likely to break off delicate details if that's ever a concern.  All my parts (styrene and resin) get a soak in undilluted Simple Green, a rinse under hot water, and a quick dunk in 99% isopropyl alcohol to speed up the post-wash drying process.  Larger parts get a good scrubbing with the electric toothbrush and some Comet (with that, you just have to use the brush again when you're rinsing to make sure you get all of the Comet residue off).  I could probably get away with doing less, but misjudging the likelihood of paint adherence issues can cost me a lot more in terms of time, so I just do it with everything, regardless of how new it is. YMMV.