Opel GT Protective Ignition Relay installation:
If the ignition switch is verified to be in working condition, the first protective action recommended is to install a protective 4-prong 30 amp relay in the starter circuit. An inexpensive relay will take up the brunt of the current when the starter is powered, keeping it out of your valuable original GT ignition switch.
The most readily available is the Radio Shack #275-226 (costs about $6).
The circuit schematic for installing this relay is as shown below.
To install, you will need to assemble a harness, with 3 short wires, 4 clip ends and 2 eyelet connectors, to connect to 3 relay terminals, 1 solenoid terminal, 1 round solenoid battery post, and a (suggested) round ground on the chassis. The existing ignition connection will be transferred from the starter solenoid to the new relay (per schematic).
A good place to mount the relay is above the starter, on the under-hood side engine area.