Tried Googling this and I just get conflicting opinions. Is a permanently lit Glow plug light on the Dashboard a MOT failure ? If its of relevance its on a 2010 Suzuki Vitara. I would appreciate an informed response.
Yes a warning light is a fault thrown up on management system which is a mot failer.
You don't know if that is a major or minor fault.
Maybe that's where the confusion is.
Ask garage to look at it first then decide how to proceed.
It passed every year, that said it was around a decade ago now, I don't know if the rules have changed. AFAIK only red warning lights or lights that could indicate a problem with the emissions or safety will fail. But I would give your MOT station a ring and ask if it's an automatic fail or not.