Sounds like you have an irregularity in your car's power distrobution.
Often times when you install ANY set of gauge overlays, you clip down the celica's gauge Hood
onto the wires protuding from your new indiglo gauges... and without a washer between this area, after time your gauges get warn and the power begins to fluxuate.
because of that fluxuation, your gauges begin to start doing strange things. - in your case, they flickered and burnt through their own wire casing.
the way to provent this would have been to make sure your gauges were securly fastened so that the electronics between your celica's gauge boot did not have a chance to move around when you drive... but not so tight as to "crimp" the wires.
I currently have this problem happening with my set of gauges... for the past 12 months
Even after 12 months, they have not worn out and still work great!
the only times when they flicker/change color or turn off and on are when the weather is extreamly cold or Im making an over 100mile driving trip (from Los Angeles or Las Vegas or even San Diego)... but its no major problem
for the most part, my AC Autotechnic Gauge Overlays work flawlessly... it was possibly one of the easiest installs I could have done - and it always gets compliments from people riding shotgun