Using a tester, measure the voltage between the connectors and chassis ground.
Connector & terminal
(B420) No. 7 (+) — Chassis ground (−):
(B420) No. 24 (+) — Chassis ground (−):
(B419) No. 12 (+) — Chassis ground (−):
Is the voltage 5 V or more?
Repair or replace the short circuit of the harness.