Additional Fuse Panel

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Additional Fuse Panel Empty Additional Fuse Panel

Post by Hawk03 on Tue Jan 22, 2019 10:27 pm

I want to add an aux fuse panel, one hot and one when the key is on, so I can hook up power door locks, trunk, stereo, gauges and other things I might add in the future. For the things I want power when the ignition is on, do all I need to do is run a power wire from the IGN or ACC port on the stock fuse block to the new aux fuse panel? Seems too easy that I feel like I am missing something.

These are the boxes I saw that could be used.

https://www.repairconnector.com/products/4-Slot-Fuse-Block-for-ATO-and-ATC-Blade-Fuses-With-Brass-Terminals.html

https://www.amazon.com/6-Way-Blade-LED-Indicator-Protection/dp/B00QMTAZ1W/ref=pd_cp_263_3?pd_rd_w=JSgUR&pf_rd_p=ef4dc990-a9ca-4945-ae0b-f8d549198ed6&pf_rd_r=9M90444D8PSFDHYDCK23&pd_rd_r=72a27ee5-1eb0-11e9-8739-9941e184f583&pd_rd_wg=o1G4k&pd_rd_i=B00QMTAZ1W&psc=1&refRID=9M90444D8PSFDHYDCK23

Additional Fuse Panel 21693964774_65a18a905f_k

Do I need to add relays? These threads talk about adding relays but not sure if I need them.

https://www.chevelles.com/forums/27-electrical-wiring/144237-help-wiring-extra-fuse-panel.html
https://www.chevelles.com/forums/27-electrical-wiring/145904-added-fuse-panel-pics.html

I'm guessing I will need an always hot fuse box for my door locks and trunk. Where is the best place to run the hot wire from? The above threads say to run it from the horn relay but I'm not sure our gen has a horn relay.

thatfnthing - thanks for your suggestions below.

thatfnthing wrote:The first thing to consider when adding something electrical is the expected current draw of the thing you're trying to add.  Your primary options would be:

1. Tap into an existing circuit.  You could get away with this if you are adding something with a very small current draw.  For example, you could simply splice an LED into the instrument panel lamp circuit, especially if you've lowered the normal current drain by switching all the other lamps on the circuit to LEDs.  In this case, you've drastically lowered the possible maximum amount of juice, so there's capacity to spare.

2. Add a new circuit. This will involve exactly what you describe above -- a new feed from the batt/alternator (or ignition switch or existing fuse block) running to an inline fuse or a mini-fuse block.

The next thing to consider is when the thing needs to have power.  If the answer is 'always' (i.e. even with the ignition off), you can run straight from the batt/alternator to the fuse, and then to the device.  If the answer is 'only in run' or 'only in accessory', then you are looking at splicing directly from the appropriate feeds from the ignition switch, then to the fuse, then to the device.

Last thing then is wire gauge.  This will be determined by the total amount of current the circuit is expected to carry for any length of time.  Too small a wire gauge, and the wires will run too hot and introduce too much resistance, which will play hell with electronic devices and sensors.  I tend to go more conservative than the factory, so I use roughly this scale:

1A or less = 20ga
1A to 5A = 18ga
5A to 10A = 16ga
10A to 15A = 14ga
15A to 20A = 12ga
20A to 30A = 10ga

Also be aware that the ground wire will need to be the same gauge as the feed.

And a word of caution: Under no circumstances should anyone just add stuff to an existing factory circuit and put in a larger fuse.  While the fuse will allow the larger amount of current through, the wires were sized according to the original expected load.  Pulling more juice through a wire that's too small will create heat.  LOTS of heat.  Possibly even enough to melt the insulation or wiring, or even start a fire depending on how much current you're trying to stuff through them.
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Additional Fuse Panel Empty Re: Additional Fuse Panel

Post by thatfnthing on Wed Jan 23, 2019 11:27 am

Everything depends on the total draw of what you're planning to add.  Gauges and LEDs draw very little, door locks and trunk release draw a fair amount, but only for an instant, and power windows, seats, and ABS draw a huge amount.  Stereos can run the gamut depending on how loud you want to be.

If it's only a marginal draw you're adding, it technically CAN be as simple as branching a subpanel from one of the existing fusebox ports.  The issue with branching off from the BAT, ACC, or IGN ports is that 1) they already have predetermined fuses (20A, 10A, and 20A respectively) and 2) there are already loads on those circuits that have to be deducted from the fuse amount to see what the remaining capacity is.  And you don't want to push it right to the edge, either.

You will be best served by adding a separate fuse box for each mode: constant hot (BAT) and ignition only (IGN).  This way you can size the wire feed for what you plan to run off of it without having to worry about messing with the cars existing circuits.  If you run the BAT line from the horn relay (yes, you should have one on the firewall to the right of the brake booster), it will be protected by the fusible link that feeds the horn relay, but while you can pull more amps than the fusebox ports would allow, you still can't get SUPER crazy with it because it is also feeding most everything else in the car from the wire between the starter and horn relay.  If you are pulling monster amps, a new line (and fusible link) should be run from the battery or starter.

For IGN, it's slightly more complicated -- you can tap directly into the 12ga PNK or ORN wires coming from the ignition switch (both should be hot in RUN), but again, it's better than the fusebox port but there's still a limit to how crazy you can get.

This is where relays come in.  A relay is simply a small switch that throws a bigger switch.  Rather than tax an existing circuit beyond its capacity, the existing circuit can be used instead just to trip the relay (which draws hardly anything).  The relay then does the heavy lifting and the 'big' switch turns on the power to whatever device is being supplied from a line that might run back to the battery directly.  This is how power seats work (in modern cars anyway) -- a relay is tripped by a small amount of current, and it turns on the main power to the seat motor from a bigger wire.  Relays are super handy, and can be used for all kinds of things, including reversing power (i.e. turning stuff off instead of on) and switching between two devices.  I even use them in my house wiring.  In your case, you could even run a large feed from the battery to both your new subpanels, and a relay put on the IGN one so that the car's ignition switch turns on the flow of power to that panel, but the power actually comes from the battery.

Sorry to be long winded.  Smile

So step #1 is: what devices do you want to add, when do they need to have power, and what does each draw?


As an aside, your fuse box appears to have a considerable amount of corrosion.  Does everything work properly?  I know mine had less and it still gave me all kinds of headaches.  This might be a good time to consider rewiring the whole car and adding your additional circuits in the process...
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Additional Fuse Panel Empty Re: Additional Fuse Panel

Post by Hs1973 on Wed Jan 23, 2019 3:06 pm

I just redid the wiring on a friends 68 camaro with a kit from one of the major suppliars of wiring kits( i Think painless wiring but not sure) anyways it was Real easy to work with and had all modern fuses and all modern accessories circuts you could ever wish for including power Windows/ doors, aircon, stereo, ekstra fans etc etc. I took me 3 weekends to rewire the whole car, and all is up to modern standarts now whatever accessorie he wants to ad. And no more Electric Gremlins and dim lights and brittle wiring. 

I redid my own with complete new wiring from from elcamino store, its all original style and works like it should. However i wish i had knows about the modern wiring kits, because it is Way better without he modern fuses and ekstra circuts. So maybe it would be better to rewire the whole thing, its really not that difficult when you get going and take your time. Regards Henrik.
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Additional Fuse Panel Empty Re: Additional Fuse Panel

Post by Hawk03 on Wed Jan 23, 2019 8:09 pm

Great information, thank you! I will need to read, re-read and probably read again before I can comprehend everything. Cool

That is not my fuse box, I took the pic from another thread. It was easier then me trying to take a picture of mine.
https://www.g3gm.com/t9677-universal-wiring-harnesses
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Additional Fuse Panel Empty Re: Additional Fuse Panel

Post by thatfnthing on Thu Jan 24, 2019 9:50 am

Oh, yes, I see that was SonOfTheGrim's. Frankly, it amazed me it worked at all. I wonder how he ever made out.

Feel free to hit me with any Q if anything doesn't make sense or needs more explanation.  Happy to elaborate!
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