I think you must ignore the B3750 code, it is quite common on the early Vectra C models.
Maby the ABS connector is the cause, as sugested in this feild remedy.
Field Remedy: 1537
Subject: ABS wiring harness connector - Poor contact
Models: Engines: Option:
Vectra-C 2002...2003,5 All All
Complaint: Failure of instruments while driving, swinging of instruments, vehicle will not start, ABS warning lamp lights on, problems while storing trouble codes of ABS wheel speed sensor.
Cause: Poor contact of wiring harness connector ABS control unit.
Production: As of MY 2003,5, modified wiring harness connectors are implemented to production.
In case of customer complaint check the contacts of wiring harness plug ABS
to ABS control unit with the test cable which is to order.