Adding speakers to truck

This may seem silly, but I am going to replace the dash mounted speaker in my truck. The old speaker is junk. I have replaced the original radio with a Pioneer supertuner 3,200 watt output. I replaced the door mounted speakers with Jensen 6x9's, drilled holes in doors and added 4'' tweeters. I made a custom box for behind the seat added jensen 6x9's and 4'' tweeters also.( I know it's the typical redneck deal )
$100 truck $500 stereo. Anyhow I have a good speaker that is the same size as the one that is mounted in the middle of the dash. I can remove and replace it very easily. But I am unsure of what lead to use. I think I should use the right rear, it being the futherest from me. Anybody ever tried this and or have any ideas about it. Maybe a dumb idea, but I have the parts and the time. I am sure the amp will handle it. Please advise. Thanks