its probably the heater plug (gloplug) relay wearing out.. not uncommon and the traveliner I picked up last night has the light on all the time when driving.
solution is replace the heater plug timer relay
if it goes completely (like mine has) the gloplugs overheat and can deform making them impossible to remove... a repair job that (at its common worst) requires the head removing to extract the gloplugs and costing hundreds of pounds
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