DO NOT sell to the OEs auto manufactures. You will loose in the end. To many famous examples to list. HOWEVER, find companies that supply to the OEs. Namely Tier-1 suppliers. That is where the money is.
ALSO, try NOT to sell the patent. Work with a patent leasing agency or group. This way, a good group will be a legal protection for your patent idea. Now, the Tier-1's or the OE would take notice once the idea is utilized in a product. The brain-child of Stow-n-Go seating wasn't born over night either. Rather it had it's history as a rumble seat or the odd seat in the back of pre-1980 station wagons. The patent novelty of the Stow-n-Go was the pop-up like chair on support legs and the smooth level action of folding that older technology folding seats didn't have.
With all that said, your search will take time to find a reliable firm. Sure, like anything, it does cost money to make money. I've been on both sides.
Now, with that said, new USPTO patents are only good for 17 years as long as the renewal payments are kept up. Patents use to be 50 years and with no frequent renewals. Should your patent reach 12 to 14 years of age, the Tier-1's and OE's are already at work implementing your patent into their products ready to roll it out the month AFTER it expires on the 17th year.
Like I said, I've been on both sides, sadly. In the course of my career, 3 patents ideas were literally stolen from under me and my co-inventors by greedy managers or prying eyes. It would have put my total near 20 and 8 globally. 2 patents of mine are used by people every single day.

Those the ones I'm more happy about.
MY mentor ...
Stanford R. Ovshinsky - Wikipedia He is known as the greatest inventory in North America since the days of Edison. Without him, there would be no DVD/CD writers/players, no flat screen monitors/TVs, no flexible solar panels (and a cheaper way to make them and get more energy), no cell phones because his battery patents got it to the size to fit in your hand, and the main inventor of NiMh batteries! Like Edison, he had no formal College or university training/schooling. He did it all himself to read, experiment and understand! Stanford will be missed greatly.