'88 300E Octane Dial

[Air&Road]

10 or more years ago, I read about the resistor in the wiring harness near the master cylinder. The resistor is a signal to the EZ ignition control that determines spark advance. I learned that removing the resistor offered maximum spark advance, thus performance and economy gains if using high octane fuel.

I removed the resistor at that time, given that Premium was probably a $1.30 at the time.

Since putting my 300E back on the road as a work car and given TODAY's fuel prices, I put the resistor back in place and have been running with no detonation on regular gas.

I remember reading at that time that on some cars delievered in parts of the world other than the US, a dial was installed that basically placed different resistances at that location in the circuit based on dial setting. This allowed for operation in parts of the world where octane availability was quite low.

Does anyone know anything about this dial? If a person knew the particular resistances involved, it wouldn't be difficult to fabricate such a dial mechanism.

Thanks for sharing any knowledge you might have.