Ok so after searching and reading probably a million of these things I need to ask... I have a 91 z28. It has had the original motor removed along with the ECM. The previous owner took out all the wiring and the computer.

My heater fan doesn't turn on at all. I checked all fuses, and the relay. however the relay has power going to all the plugs. The fan shows power going and ground going to both sides but doesntturn on. I ran a jumper to the fan and it turned on though.

 

You didn't mention the resistor pack located on the fan box. It looks like this:
http://i.ebayimg.com/00/s/MjQwWDMyMA...U7!~~60_35.JPG

Otherwise it's a matter of checking voltage along the way and seeing where it fails to get to the fan motor.

Here's the wiring diagram, looks like there's a fusible link on the relay as well.
http://austinthirdgen.org/mkportal/m..._continued.gif

There are more at Austin Thirdgen:
http://www.austinthirdgen.org/?pid=19

 

It has power to all plugs

 

You said that you 'jumped' the motor - did you jump power and ground - or just power ?? ( maybe you've got a bad ground. ) These appear to be contradictory statements. Since the fan works when jumped with 12 volts,..... If the system was sending power correctly your blower fan would work.

Once you turn the blower control on there should be voltage thru the power wire at the blower, if not then the relay is NOT sending power as it should.

I would start over because it seems like your diagnosis wasn't complete. If the motor has a good ground, then obviously the relay isn't sending power as it should. Since the blower works when 'jumped',.. the problem is somewhere between the relay and the controller.

 

I had this issue and it ended up being the contact in the fan switch itself.Over time it becomes worn.You can take it apart after removing the control from the dash and fix it.If you do a search there was a write up on this I and others did awhile back.