Its not on the griff but on the workhorse, posting here as I should get a better chance of an answer from all the Tiv posters, Heated Rear Screen and Fan Blower both work when ignition is turned on, but fail to work when the engine is running. Any ideas why this should be?
Is it when the starter is engaged rather than the engine running?
(bump start on a nice slope to test?)
Some cars switch off non-essential power when engaging the starter, it might just be a single barfed relay of this function that is causing your problem.