Offside front for the speedometer signal and nearside front for the cruise control.
You don't need much in the way of diagnostic kit to check out all the common ABS faults - just a multimeter.
Start with a visual check of the cables and plug connections.
If they all look good then, courtesy of French Mike, you can check all the ABS sensors using the voltmeter.
The signal voltage changes from 1.7V to 0.7V as each magnetic segment passes the sensor, so jack each wheel in turn and slowly spin it and look for a sensor voltage that isn't changing as each magnetic segment passes the sensor.
Here is a hub being tested prior to fitting. The long cable was made up from speaker two core with an ABS plug and socket from a scrapper.
It can also allow any ABS sensor to be plugged into the OSF to use the speedometer as a diagnostic, and with the bit of chocblock added saves pinning through the cables when using the voltmeter.
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If everything checks out then test the wiring for continuity, and if no faults are found check the ABS modulator plug and socket connections for corrosion or damage.
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