Diagnostic Aids

Check for poor connection at the BCM. Inspect harness connectors for backed out terminals, improper terminal mating, broken connector locks, improperly formed or damaged terminals and poor terminal-to-wire connection (terminal crimped over wire insulation and not conductors).
Inspect the wiring harness for damage. Check for broken or chafed insulation.
If fault is suspected to be intermittent, wiggling harness wiring may help in locating fault.

Fig 1: Horn Relay Coil Circuit Low Chart 1

Courtesy of GENERAL MOTORS CORP.