In a series-parallel circuit with working bulbs, the filaments in the light bulbs have the highest resistance.
In a series-parallel circuit with a new strand of lights, the place in the circuit with the highest resistance is the filaments in the light bulbs.
In a series-parallel circuit, the bulbs are connected in both series and parallel. When bulbs are connected in series, the total resistance of the circuit increases because the individual resistances add up. So, the filaments in the light bulbs in the series portion of the circuit have a higher resistance compared to other components.
On the other hand, when bulbs are connected in parallel, the total resistance of the circuit decreases because the reciprocals of the individual resistances add up. So, the filaments in the light bulbs in the parallel portion of the circuit have a lower resistance compared to other components.