This guy did it:https://www.instructables.com/id/Cheap_reliable_easily_mass_produced_squibs_for_gu/
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Knowing the voltage of your source, you can figure the wattage it takes to make a section light up.
resistance will be proportional to length. Measure the resistance of a section, cut it off, and double check resistance. Use the wattage/length from the original toaster to figure out how much power is needed to make it glow hot.
Use ohms law to calculate how much power it will take to heat up.