[Hanuman]

I believe the same is true for earlier systems of the ABS, as the system was largely the same, but layout was refined over time, along with some system refinements such as the inclusion of an accelerometer later on.

The big relay that is being referred to is most likely the combination relay.
This relay monitors several inputs to give an output.

Inputs include (my notes and memory are all but absent at present)
System voltage good (10v+ rings a bell, but once on, it will stay on until the volts drop below 9v)
ABS switch not off (a faulty switch can cause issues)
difflocks not engaged
System (ABS) ok
Power on

There’s a bit more, but basics are there. If an input is not present, the relay won’t trigger. It’s the fail-safe condition.

When the car is operated normally, engine running, difflocks not engaged, the ABS light should be off.

ABS light comes ON In the following cases
-Engage a difflock, or press the ABS switch, and the system is disabled.

-Once moving, a poor wheel sensor signal will cause an error in the ABS controller which will no longer give an OK.

-System electrical supply fault


At this age, I’d feel confident that any error involving a relay has a high chance of poor solder joints in the relay itself.
Any relay running hot could be the electronic gubbins if it’s a complex relay, or simply welded contacts. I’ve lost count of the number of relays that I’ve repaired in my cars, mostly due to dry solder joints. That’s a joint that is no longer secure. Sometimes a simple repair involving reflowingbthe solder with a soldering iron is sufficient.
I’ve repaired relays for Fuel pump, lights, seat memory, etc etc.