Before relying on test data one should always verify one's calibration. There are a couple fixed situations that should measure out before trusting your readings. If you disconnect the O2 sensor you should get 0.0ma EHA. If you turn the key on, engine off, the current should be 20ma on most KE systems.

To measure current one must place the meter into the circuit. A premade harness is the easiest way but what must happen IN THEORY is that one of the two wires must be cut and the two ends hooked to each of the leads such that current flows into and out of the gauge to make the circuit.

Don't cut the wires but without a made up harness you will need three jumper wires. Pull the plug. Jumper one side to the EHA pin it was meant to be on. Place a second jumper from the connector to one meter lead, place the last jumper from the other meter lead to the EHA.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician