Why is my heat not working in my 2001 chevy s10?

I have a 2001 S-10 pickup 2.2 motor. Manual 5 speed. My heat for some reason is not working. We took a circuit tester and checked all the fuses, second we tested the power to the connector that attaches to the blower. I'm not real savvy when it comes to electronics, but the connector is a two prong type. the circuit tester only lit up when he tested one side of the plug and not the other. He told me it was the blower, so i went and bought another. Instead of taking the old one out and putting in the new one right away, i just unplugged the old one and plugged in the new. the blower turned real slow for a couple seconds and stopped. i cycled through the speeds on the heater, when i got to the third speed, same thing, started briefly and stopped. It seems like to me that there is something between the fuse box and the blower connector that is not working. Any ideas?