Dodge dakota infinity replacment speakers?

I guess you can start by taking the old speaker out and looking on the back and hopefully you will see the correct ohms written on the back. You can use a digital multimeter if its not written on the back of the speaker. With head unit on and volume turned up atleast half way you can first measure the volts and write that down. Then set the meter to measure amps and write that down. Divide volts by amps and that will give you correct ohms. Another thing you will need to know is which is positive and negative of each wire going to the speaker. You use your digital (it has to be digital) multimeter and touch the wires. If you get a negative sign shown beside the volts then the leads are reversed. No negative (-) sign then you have the leads correct. I would definetly take the door panel off and the rear panel off to find out what size speakers will fit. My Dodge Ram has 6x9 speakers in the doors. I thought they was 6" speakers when I bought the truck. If you buy a 50-90 watt RMS speaker you should be fine. I doubt seioulsy that the head unit is sending more that 90 watts to each speaker.