You can also use a DMM (digital multimeter) $20 at lowes or home depot. Since you have a DIY led setup I would recommend having one for future diagnostics.
Most likely one of your wires are touch/ grounding out.
ANEMONEKEEPER has one way.
Another... using your soldering iron, if its an electric one, touch the + side of each led. If one lights up a slight bit, that is the one grounding out.
If you have purchased/have a DMM, set to continuity test .... looks kind of like this symbol -->l-- )))
place black probe on the heatsink and red probe one any of the soldered points of the led. If numbers pop up or makes a beep that is where you problem is.
9 out of 10 times that is usually the problem. Hope this helps!