DIY Relay Box

[M Rose]

Ok, I think I understand what you are saying. You are calling the coil side of the relay the "low amperage" side and the switched side the "high amperage" side. Thanks.

The coil side is a low current circuit that uses an electromagnet to switch the high current side.

Exactly... when reading tech manuals for most automotive troubleshooting they refer to both sides as high and low voltage, when in reality they are high and low amp functions. And yes the Elecromagnetic coil is the low amperage side .

Another note, Michael isn’t the first to use negative side switches, the racing community has been switching on the negative side of the circuit for quite a while and is almost a standard now. A lot of newer manufacturers are also going this route. Every once in a while you see people complaining of adding a second accessory fuse block and not knowing how to ground it because the CEL comes on, or other problems arise, this is due to the negative side switching done inside the ECU and inside the relay blocks.

 

[jcx03]

Hi Mike,

Can you clarify what you mean by "high voltage side" and "low voltage side"?

The diagram in the original post shows +12v from the battery going through a fuse and then to both the switch (30) and coil (86) terminals of the relay. The other side of the coil (85) is I assume connected to ground through the switch that controls the relay. The other side of the switch (87) connects to the load and then to ground.

My comment was that given that the chassis is grounded on most cars it is much easier to short a wire to ground than it is to short to +12v. In the diagram there are multiple things that can happen if a wire gets grounded out.
1. If the wire from the battery to the fuse grounds then you get sparks and perhaps a fire.
2. If the wire from the fuse to terminals 30/86 grounds then you blow the fuse.
3. If the wire from 85 to the switch grounds the load turns on.
4. If the wire from 87 to the load grounds then then nothing happens, until the relay is activated and then you blow the fuse.

#3 is the state I'd worry about. Personally I don't want a load to turn on if there is a short to ground since I might not be near the truck or I might not notice it while driving.

I suspect Michael used this setup since it can save running one wire to the switch. If you were to switch the positive voltage to the relay's coil then you'd need two wires to the switch, one with +12v and one to the coil. In a negative ground setup you can just run one wire from the relay to the switch, and then ground the other switch terminal anywhere on the body. The tradeoff is the issue in #3.

Here's a cleaned up version of the switching. I also included positive and negative.

Hopefully this helps anyone in the future.

 

[slomatt]

Exactly... when reading tech manuals for most automotive troubleshooting they refer to both sides as high and low voltage, when in reality they are high and low amp functions. And yes the Elecromagnetic coil is the low amperage side .

Another note, Michael isn’t the first to use negative side switches, the racing community has been switching on the negative side of the circuit for quite a while and is almost a standard now. A lot of newer manufacturers are also going this route. Every once in a while you see people complaining of adding a second accessory fuse block and not knowing how to ground it because the CEL comes on, or other problems arise, this is due to the negative side switching done inside the ECU and inside the relay blocks.

Yup, I've used negative side switching in other projects in the past (such as my tailgate light). I was trying to understand the "high vs low voltage" terminology. Thanks again for the clarification.

 

[Maxmoua]

Here's a cleaned up version of the switching. I also included positive and negative.

Hopefully this helps anyone in the future.

I'm trying to understand this diagram. I followed Mike's video and put the white 86 to the positive terminal on the fuse block. I can't seem to turn on accessories using a negative switch relay setup. If I use a test light to the accessories terminal, the accessories light up.

 

[M Rose]

Is pin 85 going to switch them to ground? Pin 30 is hot all the time, pin 87 goes to the accessories

 

[Maxmoua]

Is pin 85 going to switch them to ground? Pin 30 is hot all the time, pin 87 goes to the accessories

Yes 85 black to terminal block which is connected to switch then to ground. 86 white to power at fuse block incoming from circuit breaker. 87 to accessories then grounded. From my testing it doesn't look like the switch is grounding the circuit to 85.

 

[ginger4x4]

ohhhhh ok i think i get whats going on here. so instead of connecting your accessories straight to the fuse block you connect them to the terminal bar? What do you do if your accessory comes with a relay installed in the wiring?

 

[M Rose]

ohhhhh ok i think i get whats going on here. so instead of connecting your accessories straight to the fuse block you connect them to the buss bar? What do you do if your accessory comes with a relay installed in the wiring?

Remove said relay from the harness, or build your own harness.

 

[ginger4x4]

Remove said relay from the harness, or build your own harness.

oh ok got it. thanks so much figured that was the answer but this stuff is really way over my head. ive been trying to find that info out for awhile on tacoma world nobody is any help. But just to clarify... i would be instead connecting my accessories to the buss bar instead of the fuse block? Thats really the only thing thats not clicking in my head.

 

[Jim SoG]

Here's a cleaned up version of the switching. I also included positive and negative.

Hopefully this helps anyone in the future.

IS the green box a switch? Why a terminal block between switch and relay?

Jim

 

[M Rose]

oh ok got it. thanks so much figured that was the answer but this stuff is really way over my head. ive been trying to find that info out for awhile on tacoma world nobody is any help. But just to clarify... i would be instead connecting my accessories to the buss bar instead of the fuse block? Thats really the only thing thats not clicking in my head.

Bus bar connects directly to ground... depending upon what I am wanting this is either done directly at the auxiliary battery negative terminal to isolate the “new” circuits from the main battery; or to frame ground if the accessories are supposed to work regardless of which battery is drawing power from.
The first fuse in the fuse block is a Hi-Amp fuse that exceeds the total amperage of all the combined accessory fuses and gets its power directly from the battery positive power, and then feeds all of the relays input power on pins 85 and 87. Pin 30 goes to accessory fuse. From the fuse goes to the accessory needing power.
Pin 86 of the relay runs to the switch, then to the bus bar.
The Accessory Ground runs back to the bus bar.

 

[Jim SoG]

Bus bar connects directly to ground... depending upon what I am wanting this is either done directly at the auxiliary battery negative terminal to isolate the “new” circuits from the main battery; or to frame ground if the accessories are supposed to work regardless of which battery is drawing power from.
The first fuse in the fuse block is a Hi-Amp fuse that exceeds the total amperage of all the combined accessory fuses and gets its power directly from the battery positive power, and then feeds all of the relays input power on pins 85 and 87. Pin 30 goes to accessory fuse. From the fuse goes to the accessory needing power.
Pin 86 of the relay runs to the switch, then to the bus bar.
The Accessory Ground runs back to the bus bar.

Time for a new drawing.....

 

[M Rose]

Time for a new drawing.....

I’ll see how good my MS Paint skills are :)

 

[jcx03]

I'm updating this thread as I've learned a lot on how to do this. There are multiple ways to wire up your accessory fuse panel, and that all depends on how you want to power the relay, and if you want to be able to use accessories with the vehicle on, or off. Hopefully, this explanation and diagram will help people run through all of this.

The basics of how this all works is this: you have a switch that you turn on, that then triggers a magnet in a relay that allows power to connect from your relay to the accessory.
The power that is used to activate the magnet in the relay is substantially lower than having the switch connected directly to your accessory. It's a lot safer this way.

This should be used as a good general overview, and I hope the explanations are clear cut enough for everyone interested in DIY & wanting a system that you can fix yourself.

Config 1 / Positive Switching

This configuration powers the relay & the accessory via the 12v fuse panel.
This configuration is great because you'll only have 1 wire PER accessory going through the firewall, and it is a low power (green wire).
You can power accessories whenever you'd like, as long as you tap Pin 2 to a CONSTANT fuse.

If you tapped Pin 2 of the Switch to a SWITCHED FUSE (ONLY ON WHEN VEHICLE IS ON, LIKE RADIO).

When the car is on and the dash lights are off & the switch is OFF, then the lower light will not be on. // Dash Lights also
When the car is on and the dash lights are on & the switch is OFF, then the lower light will be on.

When the car is on and the dash lights are off & the switch is ON, then the lower light will not be on & the upper light will be on.
When the car is on and the dash lights are on & the switch is ON, then the lower light will be on & the upper light will be on.

When the car is off, nothing works.

If you tapped Pin 2 of the Switch to a CONSTANT (ALWAYS ON, LIKE IGNITION).

Lower light is ALWAYS on & accessories can be used whenever you wish. There will be Power draw from vehicle when car is off. However, you can turn this off by turning off the circuit breaker.
When switch is on, Upper Light will turn on.

How does it work?
When the switch is OFF & the car is ON, pins 2 & 3 are not in contact with each other.
However, when the switch is ON & the car is ON, pin 2 connects to pin 3, and sends power to pin 86 on the relay.

The most important: Pin 86 with Pin 85 on the Relay activate the magnet that allows Pin 87 and Pin 30 to connect & send power to accessory.

The concept is similar to a gate.

When you flipped the switch from OFF to ON, Pin 2 came into contact with Pin 3, and then activated the Magnet in the Relay by supplying power to Pin 86.
Because Pin 86 has power, and Pin 85 is grounded already, Pin 30 can now send power to Pin 87.


Config 2 / Negative Switching

This configuration is very similar to the one above, however, instead of a positive wire going through the firewall (green wire), you have a grounded wire going through the firewall.
You can turn on accessories whenever you'd like. In this setup, since Pin 86 is already powered, Pin 85 needs to be grounded.

This configuration is great because you'll only have 1 wire PER accessory going through the firewall & it is a ground wire, which is safer than sending positive wires through the firewall.

Explanation
The upper light is Pin 8 & 2, and the lower light is pin 7 & 6.
In the current setup, Pin 6 & 2 are grounded together locally in the Cab. When the switch is turned on, Pin 8 & 2 contact, allowing the upper light to turn on & for Pin 2 to complete the circuit with Pin 3.

Pin 2 touching Pin 3 is what finishes the circuit for the relay in the engine bay to activate. In essence, by allowing Pin 2 & 3 to contact, you've allowed Pin 86 and 85 to contact, and activate the magnet in the relay, which will allow power to pass from Pin 30 to Pin 87.

If you want the lower light to be turned on, then you need to connect Pin 7 to its own power source. It cannot be jumped with Pin 8. Why? The lower light's circuit is connected regardless of if the switch is ON or OFF - all that matters is that the circuit is complete at Pin 7 & 6 via ground & power. So by having Pin 7 on it's own Positive 12v, and Pin 6 (which is already grounded by default with Pin 2), the lower light will be on. If you jump Pin 7 to 8 then the upper light will always be on with the lower light, as the lower light is always connected.

Lastly, you can opt to jump Pin 30 & 86 together, but this is only useful if your accessory is low AMPS. Why? Because pin 30 is sending power THROUGH pin 87 to power your accessory & the common relay used in this application are rated for 40A. It's also better to just separate these things so you know what failed. Remember, Pin 86 is used to activate the relay with Pin 85. Pin 30 has all the power that will power up your accessory.

LAST THOUGHTS

This can all be done with 3 pin switches as well. They're actually more simple, as you're dealing with just 2 ground + 1 positive (for switch light), or 2 positive and 1 ground (for switch light).

 

[Jim SoG]

Great info, thank you very much!

Would you mind if I copied it to another thread so others can benefit from your hard work?

 

[ryno9562]

S

I'm updating this thread as I've learned a lot on how to do this. There are multiple ways to wire up your accessory fuse panel, and that all depends on how you want to power the relay, and if you want to be able to use accessories with the vehicle on, or off. Hopefully, this explanation and diagram will help people run through all of this.

The basics of how this all works is this: you have a switch that you turn on, that then triggers a magnet in a relay that allows power to connect from your relay to the accessory.
The power that is used to activate the magnet in the relay is substantially lower than having the switch connected directly to your accessory. It's a lot safer this way.

This should be used as a good general overview, and I hope the explanations are clear cut enough for everyone interested in DIY & wanting a system that you can fix yourself.

Config 1 / Positive Switching

This configuration powers the relay & the accessory via the 12v fuse panel.
This configuration is great because you'll only have 1 wire PER accessory going through the firewall, and it is a low power (green wire).
You can power accessories whenever you'd like, as long as you tap Pin 2 to a CONSTANT fuse.

If you tapped Pin 2 of the Switch to a SWITCHED FUSE (ONLY ON WHEN VEHICLE IS ON, LIKE RADIO).

When the car is on and the dash lights are off & the switch is OFF, then the lower light will not be on. // Dash Lights also
When the car is on and the dash lights are on & the switch is OFF, then the lower light will be on.

When the car is on and the dash lights are off & the switch is ON, then the lower light will not be on & the upper light will be on.
When the car is on and the dash lights are on & the switch is ON, then the lower light will be on & the upper light will be on.

When the car is off, nothing works.

If you tapped Pin 2 of the Switch to a CONSTANT (ALWAYS ON, LIKE IGNITION).

Lower light is ALWAYS on & accessories can be used whenever you wish. There will be Power draw from vehicle when car is off. However, you can turn this off by turning off the circuit breaker.
When switch is on, Upper Light will turn on.

How does it work?
When the switch is OFF & the car is ON, pins 2 & 3 are not in contact with each other.
However, when the switch is ON & the car is ON, pin 2 connects to pin 3, and sends power to pin 86 on the relay.

The most important: Pin 86 with Pin 85 on the Relay activate the magnet that allows Pin 87 and Pin 30 to connect & send power to accessory.

The concept is similar to a gate.

When you flipped the switch from OFF to ON, Pin 2 came into contact with Pin 3, and then activated the Magnet in the Relay by supplying power to Pin 86.
Because Pin 86 has power, and Pin 85 is grounded already, Pin 30 can now send power to Pin 87.


Config 2 / Negative Switching

This configuration is very similar to the one above, however, instead of a positive wire going through the firewall (green wire), you have a grounded wire going through the firewall.
You can turn on accessories whenever you'd like. In this setup, since Pin 86 is already powered, Pin 85 needs to be grounded.

This configuration is great because you'll only have 1 wire PER accessory going through the firewall & it is a ground wire, which is safer than sending positive wires through the firewall.

Explanation
The upper light is Pin 8 & 2, and the lower light is pin 7 & 6.
In the current setup, Pin 6 & 2 are grounded together locally in the Cab. When the switch is turned on, Pin 8 & 2 contact, allowing the upper light to turn on & for Pin 2 to complete the circuit with Pin 3.

Pin 2 touching Pin 3 is what finishes the circuit for the relay in the engine bay to activate. In essence, by allowing Pin 2 & 3 to contact, you've allowed Pin 86 and 85 to contact, and activate the magnet in the relay, which will allow power to pass from Pin 30 to Pin 87.

If you want the lower light to be turned on, then you need to connect Pin 7 to its own power source. It cannot be jumped with Pin 8. Why? The lower light's circuit is connected regardless of if the switch is ON or OFF - all that matters is that the circuit is complete at Pin 7 & 6 via ground & power. So by having Pin 7 on it's own Positive 12v, and Pin 6 (which is already grounded by default with Pin 2), the lower light will be on. If you jump Pin 7 to 8 then the upper light will always be on with the lower light, as the lower light is always connected.

Lastly, you can opt to jump Pin 30 & 86 together, but this is only useful if your accessory is low AMPS. Why? Because pin 30 is sending power THROUGH pin 87 to power your accessory & the common relay used in this application are rated for 40A. It's also better to just separate these things so you know what failed. Remember, Pin 86 is used to activate the relay with Pin 85. Pin 30 has all the power that will power up your accessory.

LAST THOUGHTS

This can all be done with 3 pin switches as well. They're actually more simple, as you're dealing with just 2 ground + 1 positive (for switch light), or 2 positive and 1 ground (for switch light).

So I followed configuration 2 and my lights work but both the LEDs inside my switch will not light up. The only thing I get in the switch is the upper led will flicker one time when I turn off the switch. When I ran wires for pin 7 & 8 I ran both to the same fuse tap going to an accessory powered fuse. As I said my lights work just fine but the switch will not light up. I have checked my fuses and nothing is blown and everything else in my vehicle works as it should. Should I have run #7 & #8 to their own separate acc power? I do not want the switch to light up if the vehicle is off.

 

[Oceans Overland]

Hey! Just finished up my relay center the other day. Not as much real estate in my 2nd Gen 4Runner as a Landy, but I made it work - sort of

I thought I did everything right, and then I tested it. None of the lights, accessories, or switches worked properly. I know I wired the fuses and relays right, and I know I wired the switches correctly as well. What I completely forgot is that the switches need to be positively switched in order for the switch lighes to work.

Having everything already done, little space under the hood, all of my negatives on a bus just inches away, and exhaustion setting in, I realized the easiest way to fix it was to swap the positives and negatives around on the relays. Here is what I came up with:

 

[Oceans Overland]

Also, for you classic Toyota drivers, wiring the lights to dim properly doesn't mean running the positive from the rheostat and then the switch light negatives to a ground. That will just get you full blast lighting. You have to run the negatives on the switches back to the Rheostat as well! Then everything dims as is should!