I need this bad for the wagon.

"JGrabowMSt" (jgrabowmst) 07/18/2014 at 22:07 • Filed to: velocitystacks

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Electrical question, have some velocity stacks for your time (I want these so bad).

Anyone have any idea if I should run a fuse for the exhaust valves, or should it be fine without? They're 12v, just need to find a safe way to power them. The signal goes from the coil pack on the #8 cylinder to an MDS 8969 window switch. The window switch will have it's 12v power in, and ground, along with 12v signal and ground to go to the exhaust valves. I'm planning a 3 way switch (on/off/auto) for the exhaust valves, and I'm guessing I should fuse the on and auto just to be safe, but any thoughts? I'm pretty certain the exhaust valves will need constant power to stay open, hence my thoughts on putting fuses into the system. This is very much a "better be safe than sorry" part of the car.

I build and fix computers, but wiring cars is a new thing I'm willing to take on. I do ridiculously clean installations, so this is something that will be quite well hidden in the car, and the wiring will be invisible to anyone who didn't watch me point it out or install it. OCD is a way of life.

Any thoughts?

EDIT: Here's my diagram. I'm using a 3 way switch to control the ground. It allows the exhaust valves to be always open, controlled by the window switch, or closed. Is it safe to control the ground in this way, or should I be controlling the +12v instead?

Lets have another a third try at this:

I'm used to low voltage applications where relays aren't necessary, so this is a learning process for me. I hope it makes sense.

Normally a kit like this would be used to control a nitrous system. In my case, I'm just using it to control a given circuit by being opened or closed by an RPM trigger. Not too different from it's intended purpose. I just need to make sure that the MDS 8969 retains it's memory when it loses power. I have every reason to expect it to, but I just need to make sure. I'm looking for a thread on any forum about an install of one of these, just so I can see how they're using it.

Right now, I think the biggest challenge is running power from the battery. Since the battery is in the trunk, I need to do it under the hood, there is a battery post, I just need to keep it close to the harness, and figure out which wire is the (-) for cylinder 8, as that's the closest to both the firewall and main harness, hopefully being easy to hide. I'd love to run it from the ECU, but whatever ends up being easiest to hide will be what I do. I also need to find an ACC wire to use, I'll probably take that from behind the radio, as I plan to stash this in the center console, at least partially.

EDIT 2:

So here's the final wiring diagram that I've come up with. It's very simplified, and while I was doing it, I decided to account for certain problems, and chose to wire the dumps in series, and through a single fuse. Removes any problem of one open and one not, as that would really screw with how well the engine runs.

The selector switch for each mode just changes what triggers the relay, so it doesn't screw with any major power source directly.

The only question is if the relay is wired safely. The relay will have a constant 12v running to it, as the MDS 8969 only provides the ground. It can complete the circuit through the relay. This means there's a 12v ACC constant going to the relay, waiting for the circuit to be completed. From what others have said, this should be avoided. I'm going to send an email to MDS asking about this as well, in case the 8969 isn't the correct unit, and there's a different unit to do this with. I think it's safe, but obviously, I want to make sure 100% that it is.

TheD0k_2many toys 2little time > JGrabowMSt 07/18/2014 at 22:11

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Fuses are cheap and easy to install so why not? It cant hurt anything and you will be prepared for any weird power surges

AMGtech - now with more recalls! > JGrabowMSt 07/18/2014 at 22:19

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Exhaust valves? I'm assuming you mean something like a pre-muffler dump out and not the ones in the cylinder head? What do the windows have to do with it? Sorry I know nothing of this project of yours. But if you're going to have a 12v motor running frequently and controlled by a swith, you will need to use a relay or you will burn up the switch, I suggest the same for the windows. And fuses of course. Everything should always be fused.

JGrabowMSt > AMGtech - now with more recalls! 07/18/2014 at 23:34

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I plan to use an MDS Ignition 8969 to control the dumps. yes, they're pre-muffler.

To the best of my knowledge, I just need to wire it correctly. Do I still need to use a relay with the 8969? It can be done, obviously I'd like your opinion on that. I'm guessing yes.

AMGtech - now with more recalls! > JGrabowMSt 07/19/2014 at 02:35

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I would definitely use relays. Don't want to risk hurting your expensive MSD box. Relays are cheap and only take a couple extra wires to run.

AMGtech - now with more recalls! > JGrabowMSt 07/19/2014 at 03:16

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Also just looked over your wiring diagram. Either you've drawn it in a way that makes sense to you but not to me, or it isn't going to work. What concerns me is how you've drawn in the relays, you're missing big chunks of necessary circuitry, and have added things that aren't necessary. I will try to take a few minutes tomorrow and sketch it up how I would do it.

Our of curiosity, why are you going for rpm triggered versus throttle position triggered? Or you could do both, so that if you're just cruising or lightly accelerating and don't want the extra noise you won't get it. You could set it up so that the dumps are triggered at full throttle only above 2900rpm.

Old-Busted-Hotness > JGrabowMSt 07/19/2014 at 06:45

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Always use protection. Relay and fuse.

JGrabowMSt > AMGtech - now with more recalls! 07/19/2014 at 11:15

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I'm not really sure how I've added things that aren't necessary.

It's my goal to have some manual control of the exhaust dumps. The 3 way switch is so I can turn it off, let the window switch handle it, or just flip them to be open.

I'm going for RPM trigger because the engine is typically below 3000RPM. Even lumbering around town, it really doesn't peak often, it's really only when I get into it that I'd like to hear the noise, but at the same time, I don't want the pedal to have to be on the floor in order to get there. Add that to the fact that I'd have to then figure out how to get a WOT signal to the box, since this is my first time wiring something on a car (and lets be honest, it's not quite as simple as a car radio), I'm looking to see how it works. Moving ahead, I would probably be able to switch it to WOT more easily than getting the initial setup working, so that's a change I believe I can make in the future if I'm not happy with the setup.

Considering this is just what I believe to be a simple 12v circuit, I don't really know how I've added extra things. Is it the switch that throws you off? The relays provide power to both the 8969 and the exhaust dump only when the car is running. The 8969 receives an RPM signal from a coil pack (or it could come from the ECU if I can trace the wire easily), and I set the open/closed RPM window, and the 8969 will complete the circuit in the given range, opening the dumps, or closing them below the given range.

The off switch is for when I don't want the extra noise at all, the on switch is for when I need old ladies to frown, and the auto switch is for when the 8969 will take control. I have a few small 3 pole switches that can manage this as far as I know. To prevent any arcs or fire hazard, the 3 pole switch is only completing the ground circuit, which is to the best of my knowledge, the safest way to do this.

All that said, again, this is my introduction into car wiring. I can make a more legible version of the diagram if that helps.

mazdarati > JGrabowMSt 07/19/2014 at 11:34

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All automotive circuits need a fuse, not just to prevent damage to a component, but to prevent fires.

You should (almost) never switch the ground on automotive circuits. This is because modern cars have a negative ground where failures overcurrent (blow a fuse or relay) to the negative ground. If your switch or relay is open, you could potentially cause a fire from components that are overcurrenting, but not enough to blow the fuse. The chassis ground is there for safety to QUICKLY blow a fuse if something bad happens. Your design would defeat the fusing by disconnecting its shortest path to ground. Run the positives through the relays instead.

Some older cars use a ground switch for things like the brake lights, but that only works because the light bulbs were something of a fuse themselves. Overheat/overcurrent the lamp>lamp blows>circuit is dead.

JGrabowMSt > mazdarati 07/19/2014 at 11:37

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So I should reverse it to switch the 12V? That I can do.

mazdarati > mazdarati 07/19/2014 at 11:39

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You probably only need one relay. I'm not sure the specs of the MSD box. Does it call for one? What is the rated current output?

AMGtech - now with more recalls! > JGrabowMSt 07/19/2014 at 11:43

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It was around midnight when I first looked this over and it was a long day. But the relay controlling power to the 8969 isn't necessary, just a fuse on a [ignition] switched circuit will suffice.

The way you've drawn it up is much different from how diagrams are typically drawn up in the automotive world, so your switch wiring looks really goofy to me, which isn't a bad thing, I just have to get used to it. Otherwise it's perfectly legible. Can you tell me more about the switch and it's auto feature?

The throttle switch would be easy, just put on the same line as the toggle switch on the relay control circuit.

I think you're 90% of the way there.

JGrabowMSt > AMGtech - now with more recalls! 07/19/2014 at 12:36

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Okay, so I changed it to hopefully be safer, as explained by mazdarati.

I could remove the relay for the MDS8969, yes, so far, just for my understanding, I'm going to leave it on this diagram, and potentially make a 3rd, as I get the hang of this better.

So I'm using a relay to power the exhaust dump. The relay will be triggered by the MDS8969. This is where I'm not 100% sure I have it correct in terms of how I trigger the relay, but safety first.

The 3 pole switch I want to use to have some manual control over the dumps will now trigger the relay, so nothing is a hazard. I think this is the safest and correct way to do it, I just need to get a sense of whether I'm sending the correct signal to the relay from the MDS8969.

The Yellow wire from the MDS8969 provides a ground circuit, while the grey wire removes the ground. I think I should still have the yellow wire going to the relay, I'm not sure why I wrote grey . Fast enough learning that I've wrapped my head around relays though, i think, but I was closer the first time. Learning process, right? I'll fix that, and scan it again and put it here.

It's easier for me to learn the basic wiring this way. I know I didn't use any of the symbols or anything, but I'm used to following these, not making them. I worked in radio/tv for a long time, and I might be going back, so I'm typically not used to a system that requires a relay in the power circuit, most of what I do is super low voltage, or controlled by a box I just have to configure correctly. This kind of wiring is not something I would typically ever do.

JGrabowMSt > mazdarati 07/19/2014 at 15:08

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The MSD box doesn't have a current output. It's 12v in, and has a signal wire that either adds a ground or removes a ground. Maybe look at my updated diagram, and see if that's what I should be doing?

AMGtech - now with more recalls! > JGrabowMSt 07/19/2014 at 19:08

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Looking much better now. However, if yellow from the box provides a ground, then you will need 12v on the opposite pin (85?) at the relay and provide constant ground at the "on" position of the switch instead of "acc" switched power. Relays always need 2 power inputs, one for the control and one for the consumer/slave.

AMGtech - now with more recalls! > JGrabowMSt 07/19/2014 at 19:12

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Almost every electrical device will have a current rating. Mazdarati was asking how much amperage the MSD box will draw while it is operational. That will determine whether or not it needs to be powered by a relay. I'm almost positive it won't need a relay. You should be fine with one relay, no need to over complicate things.

JGrabowMSt > AMGtech - now with more recalls! 07/19/2014 at 19:44

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Understood. When i get home, Ill figure out how to figure that in. Im way more confident now about this.

JGrabowMSt > AMGtech - now with more recalls! 07/19/2014 at 23:18

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I'm going to end up requiring two relays regardless (true dual exhaust, one dump for each side). That's simple though, because I can split the yellow output from the MDS 8969 to go to each one, which will be identical. No biggie there. I'm going to create another diagram (#3) in order to show the final wiring in its entirety to the best of my knowledge.

The main question at this point is what relays are correct for this application? I know the fuses will depend on the draw of the dumps, which is yet to be decided. Honestly, I can't find a whole lot of technical info about the MDS 8969, and very few build threads even talk about it being used. I only heard of the box when reading a thread about a Charger that was being fed nitrous, and it all just made sense from there that it could work for me.

I'm going to shoot MDS an email and see if they can give me a few more details like what fuse rating I should use for the box itself, and to verify that I am in fact doing this correctly.

Next up I just need to pester the living hell out of Gilles until he relinquishes the Hellcat active exhaust details (whether it's WOT or RPM, or both) so I can use them in the wagon. Hellcat based active exhaust will be one hell of a thing to have.

AMGtech - now with more recalls! > JGrabowMSt 07/20/2014 at 01:49

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A lot of cars that have this from the factory open the dumps when the engine has reached a certain load threshold, which is calculated based on numerous parameters. So it would be difficult to incorporate it into your project. Pretty much any 4 pin relay should do the trick. I would stick with either Hella, Tyco, or Siemens brands. I've used those for powering lots of things before without issue. And they're good enough for the Germans, so they're good enough for me.

JGrabowMSt > AMGtech - now with more recalls! 07/20/2014 at 01:56

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Yeah, I'll just have to spend a few weeks figuring out the best point for it to go open. But otherwise, with thanks to you and mazdarati, I think I've nailed the correct wiring. The only thing I'm unsure about is the relay still.

The relay has the obvious 12v from the battery coming in, but also a 12v from the ACC circuit. The 12v from the ACC circuit will be waiting for the ground signal in order to complete the circuit. Is that still the correct way to do it? I don't see why not, and given how the MDS 8969 works, there's no other way to do it. But if it works for nitrous kits, it should work for this too..

AMGtech - now with more recalls! > JGrabowMSt 07/20/2014 at 02:08

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I just edited my last response with the types of relays I would use.

It sounds like you've got it down. Post your 3rd diagram attempt and let me know when you do, I'll check it over.

JGrabowMSt > AMGtech - now with more recalls! 07/20/2014 at 11:54

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final version is towards to bottom of the post. Should be the one.

AMGtech - now with more recalls! > JGrabowMSt 07/20/2014 at 16:19

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You will need to make sure the two dumps together don't exceed the amperage rating of the relay, if they do you will need two relays. Otherwise it looks good.

JGrabowMSt > AMGtech - now with more recalls! 07/20/2014 at 16:34

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Awesome, Ill talk to an exhaust shop about what diameter I should get, and then pick the fuses and relays based on the dumps I can find for the diameter.

It also affects what mufflers I can use to support the side exit exhaust, so Ill figure that out sometime this week and figure out what it'll cost me to finish the setup.

AMGtech - now with more recalls! > JGrabowMSt 07/20/2014 at 16:53

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Cool. Post pics/videos when it's done!