Start the troubleshooting from testing the transformer. Check for 120 VAC to the primary winding (two brown wires). If the reading is incorrect then the problem is outside the cooktop.
If the reading is correct, check for 240 VAC between the red & brown wires and for 12 VAC between the red & white wires at the secondary windings plug.
If the reading is incorrect, replace the transformer.
If the reading is correct, replace the spark module.
- The transformer Part number: WB27T10856
- The spark module Part number: WB13T10076
Here are the breakdown diagrams and Parts for GE ZGU385LSM1SS Cooktop - AppliancePartsPros.com