no power to the fuel pump when i turn the key on
 

I have a 91 chevy truck k1500.
It ran fine when i took it out of the truck. I put the motor into another truck and now I have the problem. I changed the send unit and pump initially.

Now I don't have any power going to my fuel pump when I turn the key on.
I ran a hot wire to the pump and it runs. If I put gas in the throttle body it fires up until it runs out of gas.
I changed the ecm the fuel pump relay. I ran another ground to the pump just in case it was bad.My fuels are good.
Can anyone off some other places to check.
I understand the process but what I can't seem to find is why it won't turn on as soon as I turn the key on.
https://chevroletforum.com/forum/ima...ttons/edit.gif

Put the original ecm in and tell us what it does.