Voltage switch

Hi all, I'm working on a TPS voltage activated switch for a 12v car circuit. I have found a device that does this but I want to build it myself since I know there isn't more than $5 into this device but they want $76 for it. What would you say is the best way to go about this? I simulated a schmitt trigger (555 timer) and it seems to work like i wanted it to, but now i'm thinking maybe a op-amp circuit would work better.

for background, the the switch needs to activate when the TPS voltage increases to 3.6VDC. VCC is 12VDC car system, and the switch will be driving a 12v SPDT relay

this is the exact item i am reproducing.
https://www.nitroussupply.com/proddetail.php?prod=NS-25633

thanks in advance for your time.

The said switch already contains a 20A heavy duty relay.

The sensing circuit is most likely made up of LM393 voltage comparator and the reference operating point provided either by a low termperature coefficient zener or a TL431 adjustable zener.

Remember the device has to cope with possible temperature changes of some 50 degree C or more.

Here is a picture of the inside.

I'm sure you know this and I'm not certain if this effects the design any, but the sensor supply is 5v, and you want to try and leave it as clean as possible so you don't effect readings by the ECU.