My car sometimes will not start. Is there a relay problem. on 2008 Chevrolet Equinox

Will not start at times. Wont even turn over. Sometimes if we turn off heater etc it will start. Husband thinks it might be a relay prov. Garage says faulty wiring possible.

Asked by for the 2008 Chevrolet Equinox
when it wont start check for power going to starter