Relay Panels - Ground Trigger?

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mopowers

mopowers

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In researching relay panels for rewiring my 66 Dart, I've noticed some manufactures offer an option "ground trigger" circuits. I'm just curious - when would it be beneficial to trigger relays with a ground trigger? What are some examples?
 
You can save some wire, eliminate long hot wires, improve safety, and make less noise all at the same time. It just has to be done right.
 
Anytime I activate a relay with a switch (fans, fuel pump, etc), I always trigger it with the ground side for all of the reasons above
 
It takes a complete circuit to make a light bulb glow. Usually the hot side is the wire to the socket and the socket is the ground. If you make it a corvette light socket with a return ground wire, you can switch either to make the circuit. Chassis ground is just easier to wire to save wire as the metal chassis is the ground plane, especially in the rear. So the lesson here is to make sure your ground strap is securely attached to the engine AND the chassis with a good star washer digging into the metal.
 
a Master power disconnect (relay possible) at the rear of a car? You just break the relay board circuit to the chassis ground back there with 1 wire.
 
I think the main reasons for ground triggers in this auto world is stuff like DIY EFI. Such as Holley and others, the outputs for switching are all transistors to ground.. Just as these relays are set up

THERE IS HOWEVER some disadvantages to this. If something shorts, and the circuit is not well protected, you cannot kill the power..........with the switch. So if you are, say, running some relay coils off a common 10A circuit, and one relay coil shorts, you might make some smoke before the 10A fuse blows

There is "some" concern in racing, but obviously that has been ignored. If part of a harness shorts in a crash or other malfeasance, it might activate some relays you don't want activated....like the fuel pump.

One thing you MUST PAY ATTENTION to especially when using such as control modules, EFI, etc, is polarity with solid state switching, as well as polarity of the "spike" diodes. If the thing is wired reversed, the spike diodes can blowup your control circuits.
 
injectors are ground switched too. I think it may be easier on the MOSFET?
 
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