Power-B is an optional back-up power in EU. But in some countries, it is the main powering of U-ABS (i.e. Brazil).

When switching power ON, with trailer brakes applied, vehicle at rest

Each modulator exhausts one time (the number of exhausts must be the same as the number of modulators).
ABS warning lamp on dashboard or trailer indicates a specific sequence (ON/OFF) or (ON/OFF/ON)

If not, check power supply :

Test points

(with 21W lamp)

Condition

Required value

Measured value

Comments

Power-B plug

1 - 3

ISO1185 connected

Stop lamps ON

B+ Stop lamp

If measured value is below B+ (voltage drop), it can indicate a resistance in the wiring.

Next steps :

check for oxidation marks in the connectors
check stop lamp signal in the connection box
check the continuity of the wires with ohmmeter between connection box/connectors and ECU plug. (R<5Ω for correct operation)

Power-B plug

1 - 3

ISO1185 connected

Stop lamps OFF

0V

A permanent power indicates a wrong wiring or short circuit.

Next steps :