Golf 3 Glow Plug Problem (1Z Engine)

Hello,

'I've been experiencing starting problems with my 1Z lately, and I suspect it's a glow plug issue. Whenever the temperatures drop below -5°C at night, the car is very difficult to start in the morning, sometimes requiring 3-4 attempts. The crankshaft issue has already been resolved.'

'When I turn the ignition key in the morning at the temperatures mentioned above, the glow plug indicator light only comes on briefly (less than 1 second). However, a relay in the engine compartment engages and then disengages after about 5...10 seconds, without the glow plug light illuminating. (My assumption is that this is the relay for the glow plugs located under the fuse strip in the engine compartment.) I have already checked the following things, but I cannot draw the correct conclusions from the results.'
(1) 50A circuit breaker on the circuit breaker panel checked and okay.
(2) Checked the wiring harness in the engine compartment; it's okay.
(3) Coolant sensor disconnected and ignition on.
-> As described above, the relay engages and remains engaged for a relatively long duration (15...20 seconds) before disengaging. However, the light bulb still doesn't stay on continuously; instead, it turns on briefly (t << 1 second) after being activated and then immediately turns off.
(4) Relay 109 engaged, bulb continuously lit.

Can relay 109 cause a fault in the heating system? Does anyone have any suggestions?

Best regards,
Thomas.