E30 ABS light always on

[windtrader]

I have a 1986 E30 325e, stock. It has been no-op for 5 years and I'm getting it rolling again. The ABS did work and the light operated properly but not long before being parked, the light started to occasionally gone on briefly then off again.

Currently, the ABS dash light goes on when the key is in the on and start poistions and remains on after the car starts.

What's been tried so far without success:
1) Inspected and cleaned all four wheel sensors
2) Cleaned the sensor rings
3) Inspected the over-voltage relay, the silver metal cube above the ECU, fuse wire was intact
4) checked fuse in main fuse box
5) removed and reset relays in the ECU fuse box, no testing

From reading, it seems this issue is a ECU system fault and not a sensor related issue.

What's next?
1) I can check power to ECU
2) Is there further testing or taking measurement before swapping parts?
3) Seems like there isn't much more to probe as it all feeds into the ECU that controls the dash light.

[BenHar]

https://www.e30zone.net/e30wiki/index.php?title=ABS

May help?

Ben

[windtrader]

Swapped the ABS control unit - no joy, light still on. Swapped unit is used, possibly bad.

Checked resistance of each wheel sensor, all reading around 950 ohms, in range.

What next?

1) Try another control unit
2) More wire testing at the control unit connector, checking if wheel sensor wires are intact.
3) Dive in more to the 3450-0/1 ABS schematics of the troubleshooting manual.
4) disconnect the dash light. lol

[windtrader]

Still no joy on getting ABS dash light to go out.

The sensors check OK
The sensor wiring to the control unit plug are OK
The overvoltage relay is OK
The ABS control unit is OK
The ABS hydraulic unit sensors visually look fine.

Based on schematic not sure what else needs checking.

ideas?