Generally, wiring faults or failed sensors will cause the warning light on the dash to come on as soon as the ignition is switched on though maybe in your case not until water is splashed around. This is because the system self checks and sees the fault immediately.
Faults that relate to incorrect readings eg, defective reluctor rings, mis-sized tyres, etc, tend to throw the light on once up to a certain speed.
A faulty brake switch illuminates the light on first brake application.
Going leftfield, check that none of the ABS associated wiring is anywhere near other wiring that can induce currents. When Porsche released the 964 version of the 911 it gave it dual distributors. Under hard acceleration the engine movement brought the additional distributor close enough to ABS gubbins for the HT activity to confuse the ABS.
Faults that relate to incorrect readings eg, defective reluctor rings, mis-sized tyres, etc, tend to throw the light on once up to a certain speed.
A faulty brake switch illuminates the light on first brake application.
Going leftfield, check that none of the ABS associated wiring is anywhere near other wiring that can induce currents. When Porsche released the 964 version of the 911 it gave it dual distributors. Under hard acceleration the engine movement brought the additional distributor close enough to ABS gubbins for the HT activity to confuse the ABS.
