Diagnostic Aids

When a shorted-to-battery voltage condition exists in circuit 28 and the BCM requests operation of the horns, the BCM will attempt to switch circuit 28 to ground. High current flow will result and the BCM output will go into a protective state. The BCM output will not allow itself to be activated for as much as 3 minutes.
Inspect wiring harness for damage. Check for broken or chafed insulation.
Check for poor connection at the rear defrost switch.
If fault is suspected to be intermittent, wiggling harness wiring may help in locating fault.

Fig 1: Horn Relay Coil Circuit High Chart 2

Courtesy of GENERAL MOTORS CORP.