Dashboard light aren't on after replacing with new 12v auxiliary battery?

I have 2008 Prius with 102k Miles. About 3 weeks ago i had to replace the trunk battery. I followed all the guide found online and everything went smoothly. The next morning, all the lights in dashboard area went out...completely dark. I drove to work and back home and they hadn't turn back on.
I googled it and found out that I have to unplug/plug the white cable underneath the red cap so the the light can be turn back on. It worked but the next morning for work and the whole dashboard lights were out again.
The dealer quoted me over the phone for 150$ just for the diagnostic test and who know how much they will charge for anything else.
I had been over 2 weeks since, with luck the light will turn on for a day or two and then i have to unplug/plug in the cable again.
I really appreciate all the help i can get. I called around local shop and couldn't find anything mechanics know about Prius.

 

I live in SoCal, around the Westminster area.
All connections seem to be tight enough, and i am not too sure on how to check for fuses discontinuity.
There aren't any abnormal warning lights and i also brought the new battery back to the store and had them check.
The light goes off every 2, 3 days, especially early in the morning around 6 AM.