1993 Porsche 911

The diagnostic link connector is at the passenger's footwell You need a DVOM

Diagnostic Circuit
Locate 19-pin diagnostic connector underneath cover in front passenger footwell. Use Digital Volt-Ohmmeter (DVOM) to check wiring harness continuity between pin No. 7 (Orange/Blue wire) of 19-pin diagnostic connector and terminal No. 13 (Orange/Blue wire) of DME control unit.
Use DVOM to check wiring harness continuity between pin No. 8 (Orange/White wire) of 19-pin diagnostic connector and terminal No. 55 (Orange/Blue wire) of DME control unit. If continuity does not exist, check wiring harness for open circuits.
Ground Circuits
Use DVOM to check continuity to ground on Digital Motor Electronics (DME) control unit ground circuits, at terminals No. 14, 19, 24 and 30 (Brown wires). Ensure resistance is zero ohms.
If reading is not zero ohms, repair open ground circuit. Check DME ground wires on cylinder No. 1 intake pipe and fuel filter mount. Check ground strap between body and transmission/engine. Ensure all electrical connections are securely attached and free of corrosion.