Looking for a used 1911 up to $1500.  Want original firing system. Other options are negotiable. What am I looking for old Colt, series 1 Kimber?  What others?

Buy a Dan Wesson they are all series 70 and of excellent quality with all tool steel parts and a excellent barrel and fit very tight. Also springfields are also all series 70 as are many others but I would go with a Dan Wesson Valor personally they are at the top of the food chain in the non custom production market IMO. You can buy a stainless one new for what you have to spend if you shop around.

IF you can afford $1500 you can afford a Dan Wesson.  Or you can afford two Rugers.

Dan Wesson makes nice guns though.

Will look into Wesson and ????

Used DW falls into price range?

New and used Dan Wessons fall in your pricerange. You will have to look around some to get a new Valor for 1500$ but it can be done I have bought then for that before.

Found a stainless valor 1453.
https://grabagun.com/d-wes-val-45acp-5-sts-ns.html

Not all Dan Wessons are created equal.   The Valor is a high quality model but I'm not sure the others are built to the same level.

If you want plain and simple, Colt 70 series run about $950 new on GB. They are made in batches, hard to find or more expensive at certain times of the year.

I can't recommend DW enough. Blems can be had for much less than regular guns. The Duty Treat(melonite) is worth the $200-300 up charge on models. Black Valors with duty treat that are blem run in the $1400 range. Tool steel internals, no funky extra safeties, solid guns.

Another worthy choice, used Baers. Solid guns, usually blued and it shows, but shooters none the less.

And, STI, solid guns that run, period. Recently changed over some MIM parts to tool steel, also using cerakote instead of bluing on a lot of models.

Springfield armory also, but they use a internal lock on mainspring housing and specialized mainspring and housing but this is an easy fix. Best CS in the business, lots of options. Quality isn't near the above choices til you get to the top production models or custom shop level, but solid guns.

After this, is Brown, Wilson, Guncrafter, etc....

I don't even look at Sig, Kimber, S&W or any others with extra "safeties". I also rule out any of the less expensive brands. Ruger is the only less expensive  one that is somewhat intriguing, but I've held a bunch in stores, had to pass, all had some kind of fitment issue I couldn't/wouldn't live with.

They are all of excellent quality I have owned about all of them. Besides the models that have just come out. The valors have a little more attention to detail is about the biggest difference mostly dehorn sights and finish.