Trevor.... if the remote control is working then the 12v to the Timer relay is OK.... if not check fuse.
The timer relay is, as johnc says, is behind the fuses, and is Relay 311 in Pic 1. (top large one). The complete circuit is in Pic 2 if that is any use to you, and the Timer Relay connections are in Pic 3.
When you find it, unplug it, and put a meter from pin 5, then pin 6 of the connector,(not the relay) with the other lead to earth then check to see if you have continuity when each door is opened or closed.
Having checked that and found OK, reattach connector and when door is opened and closed, pin 7 will have 12v on it when door is closed, and when door is opened, the 12v should disappear and the light comes on until the timer times out, approx 15 secs.
PS. just one point..... does the light come on when you unlock the doors with the remote control?
Let us know how you get on.
1990 GTA Atmo, 2003 Jaguar X type 2.5SE Auto, 2018 Kia Picanto GT-Line-S 1.25