Powering 8-channel relay correctly Replication Steps:


595N shift register powered by arduino
Each output on register connected to 1 of 8 relays in relay board
Arduino programmed to loop over each 8, triggering 1 relay at a time
Dedicated 5v power line connected to relay board as so 
Begin loop


Expected: LED's light and relays make contact iterating over each of 8
Actual: Occasionally relay/led fires, then immediately goes out/disconnects OR occasionally relay/led x should fire, but instead relay x+1 fires

Disconnect separate DC supply from relay board


Expected: Relays will not fire/make contact, LED's will continue buggy pattern from step 5 actual.
Actual: Relays don't fire (expected), LED's light in correct order always, no bug 



Friend who is more hardware savvy thinks it could be simple matter of Separate DC supply needed more voltage as my supply is providing enough amperage to fire all 8 contacts simultaneously. However, this board is rated for only 5V correct?

What gives?
you need a ground connection between the arduino and the relay board