T-n-T wrote:

Ok a 12 volt 1.2 amp wall transformer for example. What is the formula
to determine the amount of resistance I need to not burn up the
transformer? Because I did hook a transformer up to some resistive wire
and toasted a few transformers.

BTW, thank all of you for your help.

Ohms is a word that means volts per ampere. You have 12
volts and want the current to be 1.2 amps (or less). So
that resistance must be 12 volts per 1.2 ampere

12/1.2 = 10 ohms or higher.