T4 2.5 TDI: Starting Problems & Solutions

Hello everyone,

I have a friend's 1996 T4 bus with a 2.5 TDI engine (102 hp) parked in my yard.
The little car simply won't start; the preheating lamp is only very dim. My first thought was the ignition switch, so I replaced it, but unfortunately, the problem persists. I also replaced the preheating relay, but that didn't solve it either. The fuse for the preheating system is also okay.
Does anyone have any other suggestions for me? I've read about similar problems before, but I haven't found a suitable solution.
I would have guessed it was an ESP issue, but the faintly glowing preheating indicator light is confusing me.

Thank you very much for your help!

If the battery is too weak, it might not be able to provide enough power for the engine to reach the speed needed to start.

Unfortunately, that's not the reason either; it would have been too good to be true.

Okay, I've found the errors.

The dimly lit preheating lamp was caused by a faulty relay number 109 in slot 3.
For this reason, the MSG was without power.

Maybe this will help someone someday.