LED string lights issue

[Cajonpassfan]

So a while ago I installed an 18' string of LED lights for lower deck lighting. Got them from Micro Mark, not cheap.
Today, the first 6' works as usual, the next 12' is dim, about 1/3 output. Plugged and replugged the connectors, no difference. What's the problem, what am I missing?
Pics below... first at full power, second way reduced...
Otto K.

[railnerd]

You are seeing voltage drop in action…  Is there a way to "inject" power with these strings?

[rodsup9000]

 Otto,

   Powering the string from both ends from the same power supply should fix it for now. I think you have a connection come loose.

[peteski]

Otto, what if you power each string directly (individually)? DO they then light up full brightness?

[Cajonpassfan]

Never mind guys; yes a loose connection, just not an obvious one
Appreciate the feedbackA,
Otto

[peteski]

Loose connection = higher resistance = dimmer lights. Good troubleshooting!