Dewalt 18v drill dc988 type requires switch

usually it is a 10 or 15 on the housing and then on the gearcase usually a 20

The switch on these drills is notorious for doing exactly what you describe. One thing to check is the battery terminals on the bottom of the switch, they get bent or broken off easily. It could also be internal to the switch but the only fix is to replace it. You need Dewalt part number 152274-22 to repair the drill. It's a fairly easy repair but shop the internet, they cost from $55 to $75 plus shipping.

You can get the manual on the link below. Upper right corner next to the tool.
http://servicenet.dewalt.com/Products/Detail/DC825B

web search-dewalt dc988 schematics-click on 2nd site,{parts list and diagrams

Just buy a new Makita 18volt.

check that it isnt lock halfway between forward and reverse,iv seen it happen.

Test the brushes by catching it in a stalled condition when you have it triggered, then rotate it slightly. If it takes off suspect the brushes or a dead segment on the comutator.

If it doesn't respond to this, then consider the VSR trigger... open it and test by bypassing it when in stalled condition...

Hello,
Here is a download for the manual you want.

http://toolnet.dewalt.com/Toolnet/OMrepos/00A5C2051109D14300800003A4D6051F.pdf

You could download to a cd or print it out. Whatever is best for your workshop.

Hope this helps.

http://www.ereplacementparts.com/

Try this place, one of the sites I use for documentation.

Replacing the brushes would be the first step. You can find them on E-Bay and is easy to replace.