Custom Power Distribution Circuit with Switches and Relays

I have researched for a couple of months now and have not found what I'm looking for.

This is a proposed, add-on circuit for my 2014 5.7L Tundra. Please refer to the Wiring Diagram below. My wiring experience is minimal, and I'm looking for help and knowledge backed with math and detailed explanations to achieve what I'm wanting to do. I want to have it for additional fused circuits for future add ons, mainly lighting like LED light bars, LED ditch lights, reverse LED pods, LED truck bed lights, etc.

I do not offroad, am not looking to add winches.
I do not overland or camp out of the truck.
I'm not looking to run fridges or air compressors for extended periods of time.

Here is a list of things I want the circuit To Do:
- Turn off ALL accessories when ignition is off.
- Ground triggered style relays for all accessories to avoid running live 12v through firewall & switches
- Have ability for LED lights on switches themselves to power up
- Have a SPDT switch so that I can wire reverse lights to be On when geared in reverse, off, or On when I want them regardless of transmission gear.
- I want to protect the factory wiring as much as possible, I don't want to overload the Keyed Acc. Power Source. Which is why I have a "master relay" shown and basically, in my mind, creating extra acc. power sources.
- I don't want to overload the alternator.

Does this diagram achieve what I'm looking for the circuit to do?

Also, how do I calculate the over all amps of my proposed accessories? What is the factory alternator rated at for amps?

I don't want a pre-made circuit box with push buttons because if that box fails all circuits fail. I'd like to have ability to replace individual components should I need to. I'm planning to mount all components on ABS plastic board secured somewhere in the engine bay. I'm good with physical running wire and crimping, I lack setting up circuits the way I want them to work though. I'm new to relays.


If ANYTHING in this diagram is wrong or not necessary, please try to explain to me why.
I like math and reason, I will try to follow along the best I can. I don't want to simply be told I'm wrong, I want to understand why I'm wrong.

Just a fair warning that I may annoy you with questions. I'm a civil engineer by trade, so I may be long winded and ask for more details. But I am very thankful for your time and attention!

 

To figure out your amperage if you know the wattage it’s simply watts / volts. I’m a power plant electrician and I don’t work on vehicle wiring much but it seems like you’re on the right track. Without knowing what the PIN numbers are for on the relays I can’t say whether it’s 100% correct or not.

My only suggestion would to put the fuse block on the line side of the relays so that you have more wire and equipment protected by the smaller individual fuses and not relying on the big breaker for protection. It could make troubleshooting a lot easier down the road.

 

https://www.ebay.com/p/565990837

Something like this will aid in keeping it clean in the engine bay.
You are creating a lot of work for yourself with this project. Much of your wiring will be redundant and tedious, especially if relays are new to you. You diagram is lacking a 12v+ lighting feed for the actual switch LEDs (in the switch). And depending on the switch, it may need more than just ground. (It's similar but different than just a spst switch). If you're just doing straight toggles (spst) then you won't have a lighted switch, if the switch has lights, it will need more than the diagram offers.
You sure you don't want to take some "pre assembled" fuse/relay box and amend that to your needs? So many options for adding switched relay circuits in the aftermarket. You just feed the constant and your master relay to those and implement your switches as planned. It will still be isolated like you want and save you a shit-ton of time. Otherwise, here are some custom examples you may want to model yours after. The reverse lights will need both 87a & 87 for you to accomplish you goal there.
You should diode isolate the coils of the relays too so as not to get a false trigger or bleed across the coils can cause battery draw.
Also, I believe the alternator is ~175a
And each accessory will have a rated fuse. For easy or calculation, just add those rated fuse values and that a number you will never exceed for draw.

 

I'm not worried about it being tedious. I actually like routing, crimping, and the idea of making this circuit. Relays are new to me, but the physical aspect of hooking them up is something I'm ok with. I just want to make sure I'm placing and wiring things in the proper location of the circuit.

But, which parts are you saying is "redundant"?

I know the diagram is lacking wiring for LED indicators on the switches. That is the next step to make sure I get right. Along with the correct way to wire in the reverse pods to function like i want.

How would I incorporate the "diode isolation" you're mentioning? What would that serve? I've yet to see a setup like you shared in your photo show that.

 

Redundant are the power feeds to the relays and the negatives from the buss bar. you can run one wire (fused) from the battery to the first #30 relay and jump from #30 to #30 and so on. Same with the #87 output of your master relay. You can skip the buss and wire directly to the first relay, and jump down the line. This is where something pre-assembled might help. But I get it, if you do it all yourself, you have complete control and that's a nice way to give yourself options.

The need for diode isolation occurs anytime you are feeding pre-existing circuits or adding cicuits and keeping a constant 12+ on the coil (waiting for negative triggers. Our trucks are negative ground, therefore, the electrons are moving from the battery negative, through the chassis/frame, into grounded wires, and to the point of connection to a circuit (relay coil) or directly to the negative side of the load. The light comes on if there is a path (positive) back to the + side of the battery to start again. The coil is a simple electromagnetic switch. To prevent any possible bleed through that magnetic connection, you put a small diode (one-way voltage switch) so that the positive and the negative of that magnetic switch, never have a chance at crossing the coil terminals and backfeeding. It is a safety measure, not necessary, but if you want to do it right once, and never be chasing down weird draw or anomalies from added circuits, put in the diodes. You will need to diode isolate the triggers for your reverse lights based on how you want it to function. This will prevent backfeeding voltage into truck's OEM circuits too.

Here's a pic

 

Is the diode held in by friction only?
How do you know what size diode to get?
Do they make "pre" diode isolated relays?

 

That diode isn’t doing what you think that it’s doing. Those are what’s known as “fly back diodes”. When the power is shutoff to the coil the magnetic field collapses and can send a voltage spike back through the system Known as an “inductive kick” possibly damaging sensitive components. The diode prevents the voltage spike from occurring.

to prevent back feed the diode would have to be placed in series with the circuit.

 

Yes, two separate, and different isolation applications one at the relay, the other at the tap to the existing circuit (in this case the reverse). The point is the same however, to protect both the vehicle and the circuit integrity.

You just insert the diode into the connector before you crimp it. In a premade harness you would solder it.

 

I understand both of you about the purpose of the diode.

But, can you state very simply where the diodes need to go? Pin numbers? Wire colors?

Where in the circuit, and where on the relay, should the diodes be inserted?

Literally, what kind of diode do I need? Are there different sizes, ratings? Are they color coded?

 

It goes across the 85+86 coil terminals of the relay, bandside to 86(+), barrel side 85 (-)
A simple 1amp automotive diode is all you need for the coil. They are not color coded ( those are resistors) like this...

https://www.ebay.com/itm/10-PACK-ON...ECURITY-AND-AUTOMOTIVE-APPL-D1A-/152695284615

The circuit placement is a little tricky if you don't understand how it works or why you are doing but so... You need to first know the polarity of the circuit (positive or negative). If positive, then you will have to install two diodes to isolate the circuit.you put them at the point of splicing into the wire. This is a "rough" sketch..lol


These diodes will be probably 3a or 5a (or more) based on the load of the circuit.
Hope some this helps.

https://www.ebay.com/itm/10-PACK-SI...ECURITY-AND-AUTOMOTIVE-APPL-D6A-/152695291747