My tip for spare relays

[B-Dog]

Just about any automotive style 4/5 pin 30/40a relay should work. Here are the ones that I used for a tad less money:

24v:

https://www.alliedelec.com/product/te-connectivity/1432795-1/70199412/

12v

https://www.alliedelec.com/product/te-connectivity/1432790-1/70198901/

Spankybear is correct, without a flyback diode, the coil will generate some voltage on discharge . I'm no electrician but the only instance I personally ever witnessed that as a problem was on a solenoid (much larger coil than a relay) and the voltage bounce was sending my PLC multiple inputs. I'd be floored if anything in these trucks could be effected by such a thing, especially an A0. But, if the factory engineers spec'd a diode then who am I to say otherwise?

 

[spankybear]

Spankybear is correct, without a flyback diode, the coil will generate some voltage on discharge . I'm no electrician but the only instance I personally ever witnessed that as a problem was on a solenoid (much larger coil than a relay) and the voltage bounce was sending my PLC multiple inputs. I'd be floored if anything in these trucks could be effected by such a thing, especially an A0. But, if the factory engineers spec'd a diode then who am I to say otherwise?

Industrial electronic tech here... I have seen switch contacts burn up switching 24 volt ice cube relays coils. I am thinking the engineers of this system wanted to protect the switches and what not.

There are some of these automotive relays that have resistors across the coils. The diode is better but you can't switch the polarity around on the coil. The ones with the resistor are easier to find in the after market world. Its no issue to switch polarity around as the coil itself doesn't care one way. Just a note if you are adding a relay.