What would cause my 1999 mercury 175hp outboard stall when loading onto trailer?

Question edited for clarity.
Question moved to model category.

Most of the things you swapped out would not have caused that.

Here are a few ideas

https://www.google.com/search?q=1999+mercury+mountaineer+keeps+stalling

It would have been better to pay for diagnostics using a pro grade scan tool computer. They can record what happens.

https://www.google.com/search?q=auto+electrician+near+me

..

Question edited for a lot more clarity and correct spelling of the maker.

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To easily access an Owner's Manual with consolidated information specific to your Mercury engine - agree to the terms and fill out the form below.

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On this page you can free download more than 80+ operation, owner's, maintenance manual, service and repair manuals for Mercury outboard motors in PDF.

mercury 20 hp outboard manual for sale - eBay

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1997 Mercury 20 HP 2 Stroke Outboard Shop/Service Manual on DVD! Brand New ... Mercury 200 Outboard Motor Parts Manual - 20 HP - 1976 - 3537531 & up.

Mercury Outboard 20 HP (1972 - 1989) - Haynes Manuals

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This may sound funny, but for a while, Yamaha put a steel bolt in the aluminum casing on the side of the motor. dissimilar metals caused extreme corrosion inside that affected operation. Check out Boating forums on Yamaha.

Hey Barbara,
get one of these manuals...you will be glad you did.. (professionals use these..they don't know everything)

Force Outboard Manuals by Seloc 1984 1999

Mercury Outboard Manuals by Seloc 1965 2014

Hey Pablo,
get one of these.. it will be invaluable...

Mariner Outboard Service Repair Manuals by Seloc 1977 2004

Box clogged?

Your carbs are probably dirty. Remove the carbs and clean out all jets and passages with carbcleaner and compressed air.

not sure here as i normally answer car questions but if this engine is of the new generation and its all electronic then it has to be plugged in to locate the fault .My outboard was playing up like this with loss of power and the dealer wanted a small fortune to repair the pump which feed the fuel injection system so i took it apart and made a new valve for it out of a piece of fishing hook plastic wrapper and a bit of copper wire hook type thing i made and that was about 5 yrs ago and its still running fine

If you have a stick shift, you rent a 2 wheel tow dolly and run the front tires onto it and strap it down. Put the truck in neutral and away you go.
If you have an Automatic you want all 4 wheels on a flatbed or tow trailer. You rent a car hauler trailer and piggyback the truck onto the trailer. A good rental will know the weight and rent you the right trailer.

should be on the side with a lever but could you give me more info please