Just looked it up, It sounds like the write one THANKYOU!!!!!!!

The credit thing and the car in lake description matches "The Junkman":
http://www.imcdb.org/movie.php?id=84184
The car with gullwing doors:
http://www.imcdb.org/vehicle_7478-Bricklin-SV-1-1974.html
Kind of things seen in credits (ending, but maybe same in opening):
http://www.imcdb.org/vehicle_16426-Iso-Fidia-1969.html
http://www.imcdb.org/vehicle_7507-Lotus-Esprit-Type-79-1975.html
There was quite possibly something with a horse used after a crash, but there were so many crashes in that movie that I do not rememeber exactly

Hi fellow Petrol Heads Im sending out an sos here because im starting to think ive dreamed up this film in my head!!!

The opening credits have loads of toy cars and trucks in the background

One of the stunts involves a red car with Gullwing doors (the doors were open) jumping of a ramp into a lake or something similar.

A female cast member crashes her car and is left to riding a horse shes in a black oufit with glasses.

It was made early 70's to early 80's its not alot to go on i know buts its all i can remember.

Any ideas would be apreciated.....Thanks.