what size speakers are supposed to be in the doors of my 90 single cab? and are the door speakers the only ones in the truck?

 

The door speakers are 6.5". I do believe that those are the only speakers in your truck. if I'm not mistaking it wasn't until a year or 2 later that speakers got installed behind the seat. Doesn't hurt to look though as I am not certain. Would be in the corner behind driver/passenger.


Edit: Also it doesn't hurt to use the SEARCH feature on this website. There is another Speaker question on the Front Page also...

 

I went to a sound shop looking to upgrade the speakers in my truck. The guy looked out the window at my truck and said that it had 6" rounds in the doors factory. When I pulled the panel later, the hole was for a 6" but other speakers have been installed. Those are the only speakers in it, until I can stick more in it. I looked at some 6x9's and some subs to fit behind the seat. I've also been thinking about putting some 6x9's in the lower - outer corner of the door, beside the seat.
In answer to your original question, only the two (one in each door) and 6" rounds OEM.