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Discussion Starter · #1 ·
Need some schooling on this. I want to order a Leash street/strip board while he's still making them and would like to know the benefits to one vs the other.
I'm going to start wiring from scratch with this board. Procharged motor, holley efi with holley dash, possibly water meth, elect fans and water pump, transbrake. Probably belt driven pump.
Will be using relays on board for everything on car. Some advice would be appreciated so I can get this ordered.
 

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Which way is your holley setup to switch those items?
That will tell you the board you need.
For instance my bs3, the fan control is low side meaning it grounds the relay. The main fuel pump control is low side so it also grounds the relay thru the ecu. The secondary fuel pump is a high side control so this powers the relay.
So depending on what trigger I'm controlling I would power some relays and would need to ground others thru the ecu.
I hope that helps guide you, I'm less familiar with the holley system so perhaps you can use all ground or power outputs to control all of these items on your system.
 

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Discussion Starter · #3 ·
Starting from scratch. Don't have the ecm yet but there are both negative and positive triggers available. That being said what's the benefit of wiring for one or the other? Guess that's what I'm unsure about.
Having a blank slate like I do what would be the preferred method?
 

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A relay board is used when you're using a switch to power on a load (water pump, fans, etc.). The benefit, in my opinion, of running a negative triggered relay is that you dont have to run power up to a switch panel, or to a single switch. The entire panel could be grounded with no power. Less chance of shorting or fire.

It also allows you to run much smaller gauge wire from the switch to the relay, because it's a trigger, it doesn't need to be bigger gauge wire designed to carry a load. Example: if you have a fuel pump in the back of the car you can put a relay next to the pump, and run a tiny 20gauge trigger wire all the way up to the switch panel, if you chose to. If you didn't have a relay back there you'd have to run a 10guage power wire the length of the car, and that wire would have 12v on it the whole time you have the pump on. Not as safe to do, in my opinion.

The relay also acts as a protection circuit, as it will blow if the load exceeds the relay's rating. Most of these panels have in-line fuses, though, and that lets you tailor the fuse to the load that should be appropriate for the circuit. Those are the reasons a relay board is nice.

So you have a switched ground triggered input, and a 12v input, and then one output to the load. That's it.

If you have something you're just running power to and grounding the other side, then just put a fuse on the 12v side. No need for a relay.

If you haven't done this before I would suggest making a schematic for yourself. It helps to keep everything in order in your head as you go through laying out each circuit. Just think of it like this, there are many individual circuits in the car. Some will inter-connect. It's helpful to draw the schematic so you can keep track of it all.

Hopefully someone with more experience than I can chime in and help you out also. Good luck.

Need some schooling on this. I want to order a Leash street/strip board while he's still making them and would like to know the benefits to one vs the other.
I'm going to start wiring from scratch with this board. Procharged motor, holley efi with holley dash, possibly water meth, elect fans and water pump, transbrake. Probably belt driven pump.
Will be using relays on board for everything on car. Some advice would be appreciated so I can get this ordered.
 

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In my book there are advantages and disadvantages to hot/ ground switching. If you are running a switch panel that simply runs relays, you can individually fuse power to each switch, and run trigger wires to the relays. Thus, if something shorts in the trigger circuit, it "should" blow that one fuse INSTEAD of triggering the relay to "on." IE if you run ground switching, and one of your switch leads grounds, the accessory will stay on. This may or may not be dangerous, depending on what it is. If it triggers your nitrous solenoids, LOL, might be "interesting."

The example above of the pump relay is only valid if you have a trunk battery, otherwise, you should run the pump relay UP FRONT so that line will be dead with pump off. This has nothing to do with hot or ground relay trigger.
 

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Discussion Starter · #6 ·
Little more info. I won't be using the factory ignition. Everything will be on overhead switches. Is there a scenario where wiring the relays with a negative or positive trigger affects what can be run from battery power with ignition off? Water pump, fans etc
 

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If you are going to control stuff THROUGH the IGN switch, the easiest would be to control/ trigger the relays in the hot lead. If not you would I guess have to use the ign switch to trigger one extra relay which would turn on/ off the 12V trigger power to the relays. This is going to need another trigger wire, which would defeat any "simplification" you had in mind.

Really you need to sit down and block this out to start, make a simple block of what you want to control and how. My Dart, if I ever live long enough, is street. I ran an extra trigger wire to the rear for the ground side of the pump relay. This ground will tie in with a couple of other relays, and will be grounded by the "security" relay, which will be essentially the security system. Once it's tripped, you will have to know / find the enable switch to trigger the security relay back on. A bit of fooling around by a thief will result in a blow fuse for the security relay power, and practically, the only way to swipe the car THEN is with a wrecker or rollback.

"Just an example." Most of my car will be relays.......One for IGN/ charging, the Holley HP already has a pump relay, and two more for headlights.

This means the "old" headlight circuit to the original switch is now a tiny fuse for a trigger circuit. Only thing the light switch turns on directly is the tail/ parking lamps, "just as they were" OEM.

If are not lost yet, here's what this means........

A tiny fuse in the original headlight power circuit does nothing except feed the dimmer swtich, to trigger the high or low beam relay.

Then there are two more fuses......one for each relay......to feed the high and the low beams. These actually can be replaced with plug-in breakers in the panel.
 

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In my book there are advantages and disadvantages to hot/ ground switching. If you are running a switch panel that simply runs relays, you can individually fuse power to each switch, and run trigger wires to the relays. Thus, if something shorts in the trigger circuit, it "should" blow that one fuse INSTEAD of triggering the relay to "on." IE if you run ground switching, and one of your switch leads grounds, the accessory will stay on. This may or may not be dangerous, depending on what it is. If it triggers your nitrous solenoids, LOL, might be "interesting."

The example above of the pump relay is only valid if you have a trunk battery, otherwise, you should run the pump relay UP FRONT so that line will be dead with pump off. This has nothing to do with hot or ground relay trigger.
He saved me from typing, thanks!

Send +12 to trigger the relay, ground the relay somewhere close to it's mounting point, easiest way to do it. If that +12v wire gets crunched and shorted, it won't keep the relay active forever and whatever should have been turned on will never do so.
 

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One disadvantage to using a gnd trigger would be in the event of an engine fire, if the insulation
burned off and it touched metal, it would trigger what ever it was controlling.
This happened a few years ago on a car with a nitrous system at a local track.
 

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If a fire burned off the insulation on the 'hot' wire & the bare wire touched ground, it could also start a fire.

I am not sure I understand the original question about pos & neg powered relays. Do you mean that the power circuit to the relay is completed in the neg lead...or the pos lead?

Some people think that the pos or neg lead [ ground lead/connection in most cars ] is more important than the other. They are both of equal importance & both carry the same current.

As far as energising or switching on a relay is concerned, it doesn't matter whether the switch [ or switching device ] is in the pos or neg lead. Whatever is convenient. Nor does it matter whether the fuse is the pos or neg [ grd ] lead.
 

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I am not sure I understand the original question about pos & neg powered relays. Do you mean that the power circuit to the relay is completed in the neg lead...or the pos lead?
ECU / ECMs can have either + or - , I believe that is the point of the OP question.

That is they can provide + from the relevant computer pin when the (whatever) should turn on... so you run that to your relay (and obviously other side is attatched to earth)

or conversely they can provide a path to earth when the (whatever) should turn on , so the ECM is earthing your relay to trigger it.
 

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Discussion Starter · #13 ·
ECU / ECMs can have either + or - , I believe that is the point of the OP question.

That is they can provide + from the relevant computer pin when the (whatever) should turn on... so you run that to your relay (and obviously other side is attatched to earth)

or conversely they can provide a path to earth when the (whatever) should turn on , so the ECM is earthing your relay to trigger it.
Yes that is why I asked the question. Since it can be done either way and I'm starting from scratch I was looking for opinions from people more knowledgeable than I am on the subject.
 

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Discussion Starter · #14 ·
If a fire burned off the insulation on the 'hot' wire & the bare wire touched ground, it could also start a fire.

I am not sure I understand the original question about pos & neg powered relays. Do you mean that the power circuit to the relay is completed in the neg lead...or the pos lead?

Some people think that the pos or neg lead [ ground lead/connection in most cars ] is more important than the other. They are both of equal importance & both carry the same current.

As far as energising or switching on a relay is concerned, it doesn't matter whether the switch [ or switching device ] is in the pos or neg lead. Whatever is convenient. Nor does it matter whether the fuse is the pos or neg [ grd ] lead.
So I will ask what may be a dumb question. I assumed that using a negative trigger to the relay would mean the relay completes the ground when it's sees voltage from the ecm. No?
 

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In the case with my ECU, the fans are triggered by +12
So the relay is set up with a gnd sitting on it, and when the ECU sends the +12 it completes the circuit.
Same deal if the ECU used a neg signal, you would have +12 sitting on the relay, and the neg from the
ECU would complete the circuit-some people would rather have a gnd sitting on the relay rather than +12
vs, but in my case I cant change what the ECU puts out to the fans, its the way it is internally.
 

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Need some schooling on this. I want to order a Leash street/strip board while he's still making them and would like to know the benefits to one vs the other.
I'm going to start wiring from scratch with this board. Procharged motor, holley efi with holley dash, possibly water meth, elect fans and water pump, transbrake. Probably belt driven pump.
Will be using relays on board for everything on car. Some advice would be appreciated so I can get this ordered.
What does this mean? Are they changing products or something?
 

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If the ECM is giving you a negative to turn something on, just get 12 volts to your relay from batt or ignition circuit, then run the relay earth to the relevant ECM pin/wire. When its time for that component to turn on , the ECM will earth the relay.

If the ECM trigger is positive, run that + coming out of the ECM to the relay, and the other side of the relay goes to ground. The ECM will then give + when its time to turn that component on.

Some ECMs have both ways on the same ECM, for example the ECM might give you a - to turn the fans on, and a + to turn the fuel pump on... it doesnt really matter from my point of view, but depending on your set up, a + signal coming out of the ECM might cut down on the amount of wire, as you can then earth the relay at/near the relay.

But conversely if youre using the ECM as a - to earth the relays to turn em on, a common + from batt/ign to relay area to power them up can also cut down on wire.

Six of one half a dozen of the other as they say. More people might chime in with ideas of why one way might be better than the other.

If the ECM is giving off a + though its already gonna be fused as the ECM power in from batt would be fused. (it should be! if installed right)

Whereas if the ECM is giving you - to turn stuff on, you should fuse the +ives that you have to run to the relays from batt/ign.
 
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