Using Arduino to change resistance in another circuit.

Hi,

I recently put a Haltech ECU into my car and one of the features is a cruise control wire. The circuit works between the cruise control wire and signal ground and using various resistors to simulate the different cruise control switches.

The cars current cruise control switches consist of 6 wires in a very strange connection pattern that i so far have managed to convert into discreet voltage outputs using the arduino and some programming. I thought i could output the voltage into the cruise control wire but it obviously works the opposite way by being grounded out.

I’m trying to think of a clean method to select between different resistors to simulate the different buttons using the arduino. The only method i can think of is using 6 relays controlled by six outputs on the arduino. This feels a little messy so i was wondering if anyone else has a smarter idea.

Thanks

backdoorshenanigans:
This feels a little messy so i was wondering if anyone else has a smarter idea.

Indeed, but it is only temporary, and would be a very effective way of keeping Arduino's electronics separated from the car's electronics.

Its going to be a permanent solution so probably needs to be fairly durable. The arduino is powered by the Haltech ECU so they are kinda already integrated.

I think i can get away with 3 relays by switching them in different patterns.

Use a TPIC6B595 - eight open-drain outputs rated for automotive voltages, controlled by three Arduino pins and all are updated simultaneously. Just get your grounding right.