Ford F Diesel Preheating Lamp Issue

Sounds like your glow control unit is acting up, alright. The preheating lamp staying on, engine light, and smoke are classic symptoms. When you checked the connections, did you specifically look at the cable and plug going into the glow control unit? A loose or corroded connection there can cause all sorts of weirdness. Glow plugs are heating elements which help start diesel engines, and the control unit tells them when and how long to heat. If it's not working right, you'll get poor combustion, hence the smoke. What exactly did you check so far?

Thanks for the quick reply! To be honest, I just gave the cables a wiggle and made sure they seemed plugged in. I didn't see any obvious corrosion, but I also didn't disconnect anything or test the voltage. How would I go about properly checking the cable and plug connection? I'm a bit of a novice when it comes to electrical stuff.

Okay, wiggling isn't exactly a scientific approach, haha! Seriously though, it does sound like a dodgy connection. Since you're not super familiar with electrical testing, and messing with it wrong could fry something, my best advice is to take it to a workshop. They can properly diagnose the issue and replace the cable or plug (or the whole unit if needed). It's likely a cable or plug connection, but it is better to let a professional sort it out. It will save you time and potential further headaches. Plus, they can clear that check engine light for you.

Thanks for the advice! I took it to the workshop, and you were right – it was a defective cable/plug connection to the glow control unit. They replaced the cable and cleaned up the connection. The bill came to 95€, which was a relief. No more smoke, and the lights are behaving normally. Really appreciate your help!