1976 450 SEL rear window defogger switch

When I press defogger switch it lights but does not hold down (returns to original position and light goes off).
Should the switch hold down and the light stay down?

Thanks!!!

RAfable

My '76 280S has the same switch. Once it lights it is working a timer/resistor will shut it off unless you press it again to restart the secquence.

Gympie