The same relay, the R2-5 ,is responsable for both,the rat probe heating and the TO configuration warning. If only this relay is faulty the rest ground sensing system remains ok .Remember the plane return for a problem in the Rat sensor heating.The heater must work only in flight. If is heated in ground, the Rat indicated is extremely high and the computed TO EPR too low. Is in my opinion the reason for the first frustated T.O. .The mecanic disconnect the heater, opening a CB ( posible the RAM AIR TEM.& PROBE HEATER.) but this moreover feed the TRP (thrust rating panel). But this accion is only for TO .After this ,the pilot can reconected.In this condition the Auto throtle is inop for TO.and not is a problematic condition. The TO EPR is obtener from the data chart.
If the LEFT GND CONT. RELAYS circuit breaker was open, a relays group change to flight condition but is not too mach evidet for crew.
The strobe light is the only asociated to ground sensing .