I have a Troy-Bilt pressure washer 2600 and the wires coming from the on and off switch are yellow and black going to a little box that has a yellow and black wire which ones go to Which Wich

What is your model #

clean and soak all valves if do get work do not leave solution in it over time.carb cleaner with that little straw

Could also be crack/leak in HP pump. If it were left in cold weather without antifreeze, I'd check there first. Part + labor might warrant new washer if more than a couple years old.
Sorry.

Cover soap inlet and retry. Mine will not pressurize without soap or without inlet covered.

Call us when you can be at the washer so we can trouble shoot it with you over the phone.
http://www.ppe-pressure-washer-parts.com/troy-bilt-020416-1-pressure-washer-parts

underneath base of motor look for a plug wuth a square slot,i normally use a 3/8" extension with ratchet.

If when you take the High Pressure water hose off the pressure washer pump no water will come out they you may simple have the bypass valve stuck. You may need to just remove the outlet fitting and clean the bypass valve.
It would be helpful to know the model number of the pressure washer or the pump.

My chemical supply inlet has a checkball and a spring that keeps pressure in check. There must be debris behind checkball. Easy to check by removing the fitting. If faulty and parts not available, plug fitting and add an aftermarket injector from www.pwmall.com. that you can install when you need it. Good luck

here's your breakdown and part numbers.

http://www.ppe-pressure-washer-parts.com/troy-bilt-pressure-washer-model-020293-1-replacement-parts

Turn Black cone shaped valve clockwise to increase pressure there will be a small +/- plus will increase and give you pressure.

TK U