DeWalt DC500 Shop vac

Yep, they are all words. I put them in the right order! :>D

No wiring diagram available and no service manual.

https://www.google.com/search?q=dewalt+dc500+wiring+diagram

It should be 110 volts in, and through a transformer to 18 volts output where is meets up with the 18 volt battery socket and from there to the motor.

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Check to see if the hose is clean, and that the plug on the opposite side is in.

Check the battery with a meter to see if it's fully charged.

Check the hose, and the plug on the side.

may be the carbon brushes are short or motor connectors have become bad connection by moisture and dirt by use temporay a wrong filter sometimes its a very light and simple motor johnson motor with hammer brushes
DeWALT DC500 Type 1 Vacuum Parts

DeWALT DC500 Type 1 Vacuum Parts

this vacuum is prone to battery contactor problems. Check for bent pins or (more likely) corrosion. Check batteries and radio.

Check battery contactor on the vacuum and on the battery. It is a common problem on this vacuum. Check for bent pins and corrosion.

there is a float ball or reed that closes off the exhaust port inside the canister, to prevent water from filling too high when used as awet vac. If lodged or trapped it will prevent suction or discharge in wet and dry modes. look at the housing that the filter attaches to and you will see it. if it doesnt rattle when you shake the unit up and down, it is stuck; otherwise, you must not be spinning the fan blades.

I had the same problem and traced it down to the on/off switch. I sprayed some electical contact cleaner down inside the switch and now it works normal. Hope this helps.