I work for a Fortune 500 company that deals with this process (outside inventors) regularly, though not an Automotive co. Things are a bit different than they were 40+ years ago when the intermittent wiper case happened... Most big companies now are scared to death of getting sued and dragging out legal proceedings over something that may not even be that useful to them, so they are much more careful now. The submission form you describe is how it works for us. If you contacted me directly, I would point you to the form as we have been very clearly instructed to not listen to any outside ideas like this directly. The company does not want any legal or potential legal encumbrances to ideas. The first thing the form will ask you is if it is patented yet. If not, it strongly suggests that you at least apply for a patent prior to sending us anything technical so that, once again, there is no question of who did what and who owns what. once you fill out that form with some details on what it is, your patent number, etc, it gets reviewed and routed to potentially interested divisions, so you want to be clear what industries/products/markets it might apply to. I've been involved in reviewing a couple external ideas that were sent to us via this system (though it was several years ago), so they do take it seriously at our company and follow up. Once they have collected replies from all internal parties, they will send a response to the inventor. Something along the lines of "we would like to talk more" or "thanks but no thanks". I do not know all their possible responses, but I'm sure it is in that range.
One thing to keep in mind is that if you are trying to invent something in an area that one or more companies have been working in for years (or decades in the auto makers case) then there is a pretty good chance that they have already thought about it or something similar, tried it, or abandoned it, etc. Just because you ran a patent search and got a patent issued doesn't mean there isn't something out there that could nullify it. Patent searches are by nature limited in scope so it is entirely possible to miss something even with a thorough search. And when you are dealing with an expert in the field they will probably recall what that item was and know how to find it. A company isn't likely to pay for rights to a patent if either they think they already have it covered in their patents or there is other prior art covering it that they are aware of (could be competitors/suppliers existing patents or expired ones). And in the end, a patent is only worth something if you can defend it, and that costs big bucks. It is a tough game to play at.
The best thing you have going for you is you already have a patent. That means the initial big expense is behind you. I'd start filling out those forms at the OEMs and Major Tier 1 suppliers that make sense and see what happens. Won't cost you anything but time at this point.
My $0.02 from my experience.
-Dave
