Electronic – arduino – Using the iPhone to control a remote controlled car via Arduino

All of the Remote Starter systems I have seen are aftermarket products. In fact, most auto dealers use these after market products when installing them in new vehicles. It should be easy enough to find the manufacture of yours, and send for a replacement remote fob. Once the fob is programmed to your vehicle, you can hack the contacts to your new circuit.

As far as sensing the engine running most of these units use a sample of the engine RPM (tach) and detect the pulses. The RPM outputs on the ECU of the vehicle, and is probably already tapped to use for the Remote Start unit. For the report back function, you can buy a remote fob & receiver and hack it in much the same way as your starter key fob.

EDIT: After reviewing the new information and pictures, I will revise my answer to the following:

If the led in fig 1 (lower right corner) is the confirmation of a start indicator, then a photo transistor can be optically coupled to this led through something like a short hose or tube. This can then be an input of the Arduino.

EDIT 2: In fig 1, middle of the board may be a tactile button switch to initiate a start. If this is the case, a relay could be connected to the Arduino output and wired to the tactile switch in parallel.

YOu are entering a world where Electro Magnetic Compatibility is at risk. Pay attention to the stray current spikes that radiate noise (Egress) and their influence on other circuits of high impedance (Ingress). YOu probably also have ripple or the conducted egress and ingress as well.

For radiated noise a handy tool is a small AM radio (not FM) nearby, to locate such noise issues if you dont have a scope.

Noise suppression management may include some common mode chokes to the track or pot lines. Perhaps some supply rail filtering may need to be added around the track.

I would use ferrite beads for each driver with caps after the bead and then use twisted pairs to send the current after going thru a ferrite torroid or similar common mode choke, like those used in Video cables. Its good to have a kit of parts for such issues.

Add decoupling caps to the breadboard for both sides.