Need to install a couple of relays for dome light and rear hatch release for use with my new keyless entry system. Some relays have built in resistors for voltage spike suppression which is suppose to help prevent damage to the electrical components some do not. Just how important is the suppression resistor? I already have a bosh relay without resistor, shoulld I use it or get two with resistors? Just wondering how critical the resistor is or if it's a lot of hype. thanks.

 

They're diodes, not resistors. You can easily add one to the circuit of a relay that doesn't have it already.

 

 

There pretty important actually. What happens is any thing with a coil (basically an inductor) will attempt to maintain the same amount of current through it regardless of the change in voltage across it. So when you de energize a coil like in a relay the collapsing magnetic field induces a voltage in itself in an attempt to maintain the same current through it (sounds kinda familiar dosnt it? Like how an ignitions system works perhaps? lol). Because its an open circuit that voltage spike is pretty large. This large voltage spike can exceed the voltage specs and damage things (kinda like how static shocks can damage chips). To control this as stated they use diodes (or diode resistor combinations) to in essence short out these voltage spikes. How important is it in your situation? Depends what its hooked up to but adding a properly sized diode cannot hurt only help.