Two more days to go and then the problem shooting begins.

I will first try and isolate the possibility of a short or partial
short in the system, that will be the least effort and the least amount
of digging :-D

Then I will see if I can get my hands on a multimeter to see whether
voltage drop exists in the system, if so I will maybe boost the voltage
to 14V or so, then the last ligths will receive the 12V they need, but
I will need a resistor on the first two lights so they wont get fried.

If that is not an option I will add a second conductor to the system
and wire the lights in the loop pattern, using a higher gauge
conductor.

Thanks very much for all the suggestions, will keep you posted.