Hit the gas

The project is getting to the stage where the motor and batteries are in, the high voltage wiring is done and it's quite tempting to just bodge enough of the other bits that make it go, as quickly as possible to be able to drive around.
The other extreme would be to get endlessly bogged down in smaller and smaller details, and never actually get it finished.

Modern cars are now nearly all "fly by wire" which means there's a potentiometer mounted right on the throttle pedal bracket, which gives an electrical signal as you press the pedal. That in turn makes a servo open the throttle valve under computer control.
So effectively they've caught up with electric vehicles which have used an electrical signal for decades.
Anyway, your older petrol cars (which the Insight definitely is) use a mechanical cable instead.
So then your EV conversion needs some sort of mechanical contraption to translate the cable pull action into an amount of rotation of a potentiometer. And no two makes of car have the same throttle cable arrangement, so there isn't a universal bolt on bit to do this.

One approach would have been to make something up out of bits of aluminium. But since my work recently got an Ultimaker 3D printer I've been trying to think of useful uses for it. So I CADed up a throttle box, and they generously allowed me to print it out.

The red part is a pulley, which is hopefully (I mean carefully calculated using trigonometry) the right diameter to rotate over a suitable range of angles for the potentiometer, when the pedal is pressed. There's a place to mount the return spring and the potentiometer faces the pulley and is rotated without any side load being exerted on the shaft.

Well, we only had red PPA plastic (which is fine, it's not going to get very hot under the bonnet of an EV) and this is how it turned out:

There you can see the throttle cable at the bottom, the potentiometer resting in place, and the return  spring (ahem) at the top. The pot is from my PSA bits box, but it's a proper Potter and Brumfield part normally used on electric trains so I feel quite confident about it.

The potentiometer bolts on to the inside of the lid and the lid is screwed on. It all fits, and works!  Now I just need to find a proper spring,