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I'm looking at maybe installing a relay box in my 2010 King Cab, so that I can do accessory power the right way. Out of the gate, I know I want to hard-wire my Garmin dashcam with the parking mode cable, and probably put my aftermarket rear view mirror on the relay box as well instead of having it tapping into other wires like it is now. I'd like to place some LED lights in the bed so that I can see what's going on under the tonneau cover, and maybe some 12v outlets in the bed. How do these plans impact what I want to install as far as relay box gear? What sort of changes would be necessary if I wanted to install, say, a winch or inverter?
 

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Nerd, I think thats a sound plan to start. Ideally your add-on parts would have two connections to the factory harness only, a heavy one to the battery that brings over HOT AT ALL TIMES to a fuse / relay bank and and an IGN / RUN tap to power up the accy relays and fuses for devices that are not powered continuously. Never attempt to power anything off the stock factory harness, the circuits were never sized for anything beyond what the stock factory loads create.

RE the winch, etc, that will require heavy fused cables tied directly to the battery posts, winches draw a very large amount of power when in operation. That will not be connected to your new accy fuse / relay box unless you decide to have a remote winch-in / winch-out control switch located in the cab itself.

For some inspiration, this is mine, all custom designed, engineered, hand-fabricated and wired by me.

310746
 

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Discussion Starter #3
Nerd, I think thats a sound plan to start. Ideally your add-on parts would have two connections to the factory harness only, a heavy one to the battery that brings over HOT AT ALL TIMES to a fuse / relay bank and and an IGN / RUN tap to power up the accy relays and fuses for devices that are not powered continuously. Never attempt to power anything off the stock factory harness, the circuits were never sized for anything beyond what the stock factory loads create.

RE the winch, etc, that will require heavy fused cables tied directly to the battery posts, winches draw a very large amount of power when in operation. That will not be connected to your new accy fuse / relay box unless you decide to have a remote winch-in / winch-out control switch located in the cab itself.

For some inspiration, this is mine, all custom designed, engineered, hand-fabricated and wired by me.

View attachment 310746
Is that running off of the relays in the box beneath it? In my truck, that's about where the standard relay box sits.
 

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For some inspiration, this is mine, all custom designed, engineered, hand-fabricated and wired by me.

View attachment 310746
You posted the pic, so I'm gonna ask: what's with the piece of e-tape and the multiple diodes looking like they go nowhere?
 

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The diodes are preventing backfeeding to the circuits after the relays disengage, often called snubbing diodes, sending the reverse EMF pulse to ground. No clicks or pops in the radio.
 

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Nerd, I should have probably posted the wider angle photo as well, here it is. The relays are actually sitting on top of the second factory underhood fuse block and are held in place by brackets I added. The relay sockets have "teeth" on the sides that interlock and make a single unitized assembly out of all the seven separate sockets.

310758
 

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The diodes are preventing backfeeding to the circuits after the relays disengage, often called snubbing diodes, sending the reverse EMF pulse to ground. No clicks or pops in the radio.
Curious... any wiring diagram or overhead photo how you have this all wired? Were you having clicks and pops in the radio before doing this?

Also, how easy is is to get to the factory fuse box in case something happens? I have my Blue Sea fuseblock in the same spot but it's not as big, and I had to strategically route the main power cables in a way so I could flip the OEM fuse box cover open with ease
 

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The diodes are preventing backfeeding to the circuits after the relays disengage, often called snubbing diodes, sending the reverse EMF pulse to ground. No clicks or pops in the radio.
I've never heard rectifier diodes referred to as snubbing. Blocking is the only other term I'm familiar with.
 

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Butterman, snubbing diodes disperse the millisecond EMF pulse that is created when the magnetic field around the relay coil collapses, inducing a voltage back into the circuit and up-line to anything else around it. All OEM relays that I've ever seen, have a snubber somewhere in the loop, usually inside the relay itself. This is the same exact effect that ignition coils rely on, when the 12vDC is removed from the primary coil, a powerful pulse is induced in the secondary as the field in the primary collapses. Bang, one spark plug firing cycle.

Raine, good points. No, I didnt have any clicks or pops but wasn't planning on introducing any new ones. If you look at some aftermarket relay harnesses that are prefabbed, they will have a diode in the mix, it may not be easy to see but most of the time its there.
Access to the OEM boxes underneath is somewhat impeded, I would have to cut the cable ties holding the relay bank in place, then fold the whole assembly toward the firewall and over towards the intake manifold. Its not a walk in the park but all the wiring except the main power cable comes in through the rear for easier maintenance. So far, its been in place for over a year and I've never had to access any of the OE parts underneath, so it doesn't concern me much.
 

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310771
 

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I think they were 3A 50v working voltage. Can't say I remember for sure, the ratings not super important, these are the 5 or 10 pack types you used to pick up at Radio Shack. I'd use a 50v minimum just to be sure youre not approaching or exceeding voltage ratings during the clamping event, though to be honest the transient is so fast, it would prob matter little.
 

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Actually I was asking for a diagram to see how you wired the diodes... because in the photos, it's not clear - and it almost looks like the diodes are parallel to some wire attached to the same contact (not in-line). The random piece of electrical tape hides how they're actually wired in, thus I asked for a diagram but your diagram doesn't show the actual wiring paths and diode locations.

side note: the OCD in me is really bugged about that piece of electrical tape LOL
 

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Raine, I may remove that as well, LOL, it kinda bugs me too. But I dont spend much time staring at the fuse box, its much more fun to be behind the wheel. The diodes are mounted one to each positive incoming control wire, and combined ( paralleled or bussed ) at the ground side, as they all lead to the same earth potential anyway. I dont really have a wiring diagram as I've literally been doing this type of thing for decades ( and for years as a profession, designed complex pump control and gas processing equipment as a contractor for Ingersoll Rand ), and just had it all in my head, built it, then tested and installed it. It was 100% the first time out, didn't make any wrong connections, which kind of even surprised me a little as all the prepurchased relay sockets had the same wire colours, so theres a whole plethora of reds, whites, blues and blacks under there.
 

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Still can't get a visual... if you end up pulling the electrical tape off, if you can take a quick pic I'd like to see it. You know, for science. Hahah
 

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Draw a straight line across the bottom of a sheet of paper, then seven diode symbols attached to the line at the bottom and pointing straight up. All for science, of course.
 

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310823

Down n dirty notebook sketch but you should get the idea. Just repeat the relay part 5 more times and you have 7 relays across.
 

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I'm looking at maybe installing a relay box in my 2010 King Cab, so that I can do accessory power the right way. Out of the gate, I know I want to hard-wire my Garmin dashcam with the parking mode cable, and probably put my aftermarket rear view mirror on the relay box as well instead of having it tapping into other wires like it is now. I'd like to place some LED lights in the bed so that I can see what's going on under the tonneau cover, and maybe some 12v outlets in the bed. How do these plans impact what I want to install as far as relay box gear? What sort of changes would be necessary if I wanted to install, say, a winch or inverter?
The stock fuse relay box has some extra space in there. i think you can stuff 2 or 3 relays in there. I wired up my offroad lights with a relay and used the stock fuse box to house the relay.
 
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