This is a Fluxgate compass assembly for an Autohelm ST1000, ST1000+, ST2000, ST2000+ Tiller Pilot 

Also fit ST3000, ST4000, S1, S2, S3, SPX5, SPX10, SPX30 etc

Fluxgate Compass Test

The first part of troubleshooting a heading issue associated with a magnetic north seeking compass is to ensure that items capable of producing a magnetic field have neither been positioned nor installed within 3' of the magnetic north seeking compass. 

Additionally, as the fluxgate compass features mechanical components, it is possible that the fluxgate compass's moving parts may have failed in a manner causing them to bind. This condition may be verified by executing a slow turn at a constant rate of turn through 360 degrees while observing the reported heading. Should the heading pause (i.e. not change or not be reflective of the rate or turn), then it would indicate a problem with the mechanical components within the fluxgate compass, necessitating its replacement.

Multi-meter should be set to:
(a) Resistance scale
(b) 200 ohm scale
The following procedure should then be followed:
1. Disconnect the transducer from the system.
2. Connect one multi-meter lead to the red wire and the other lead to the green wire and a reading as indicated in the test data table should be present.
3. Follow the above procedure for all the color combinations indicated in the test data table.
4. If all readings match those indicated assume the compass transducer is functioning correctly.

Compass Test Data:

Red to Green - 4 ohms
Red to Yellow - 4 ohms
Green to Yellow - 8 ohms
Screen to Blue - 8 ohms
All other combinations - OPEN

A failure would be identified should any of the above listed resistances show an open circuit (infinite resistance) or deviate from the above listed resistance value by +/- 2 Ohms. 

Should this testing not indicate a failure with the fluxgate compass, then the autopilot course computer would be deemed to have suffered a failure.