Hello, and thank you in advance for any help you might offer. 
I have constructed an outside tree design that goes on my flagpole making a 20' tall tree with 16 incandescent light strings each managed by a relay.
The board is a genuine Arduino Mega.
I can get all strings to light up individually but when I try to light multiple strands the red activation LEDs on the other relays get incrementally brighter as strands are turned on finally tripping other relays that are not in the program.
The relays are on pre built on boards with green for power and red for activation status LEDs tripped by a transistor.
The 16 relays coils are wired in two banks of 8 and powered in parallel, each bank by a separate power supply.
All relays are set to normally open operating condition and are fed by an individual pin from the controller to turn on and off.
The controller has its own power supply.
It appears to be some kind of feed back through the relay wiring, but it doesn't seem like the parallel power supply could go over to the input pin of the relay.
Am I just over driving the controller with too many relays? Relay spec is 5ma signal to trip the transistor and 20ma for the coil but coil current comes from a different supply.
Is there a feedback prevention device that I can use.
I have put a lot of hours in this project and want to get it finished but I am stumped to do anything but turn on a strand or two at a time.
Any other info I can provide to help just let me know.
I tried to attach a pic but I don't know if it worked or not.
Thank you so much for your time.