Adding a circuit to the existing fuse box - puma
Hi, I like the information here about adding a circuit. I have sourced the parts to add some work lights into the existing fuse box. I’m stuck on removing the brown cover protecting the 13mm power in from the battery without breaking it. Then I need some help with accessing the back of the fuse box to wire in the fuse link, a fuse and maybe a relay.. any help would be appreciated.
CB
[QUOTE=Toxic_Avenger;2304905]Hi Lou (and others),
On the side of the fuse block there is a thick wire and lug which bolts on with a 13mm nut - this is the power IN to the board. I haven't put a multimeter on it, but I presume it's a direct feed from the battery.
When you follow it underneath the fuse block, that wire hooks directly to two copper 'bus bars' which run current along the 2 rows of fusible links (those little square fuse looking things). NB there is heaps of spare spots, one of which the quoted post has a multimeter on (Huston, we have power!).
These fuses are a J type, and are easily sourced... this is the first piece of the puzzle.
Now let's suppose one wanted to make a new circuit which is switched on when there is ignition - we have 2 options:
1) Piggy back on an existing circuit that is ignition switched (running the risk of drawing too much current thru that circuit, and melting stuff...
2) make a new circuit, and build it to your specs!
Not familiar with the engine saver, it is likely that it's not going to draw massive power, so option 1 would be the most attractive. Option 2 is for serious players, and is undoubtedly the hard way, but something that would fool all bar the most dedicated concours d'elegance judge (if that's your thing).
If one were to want a factory appearance, and utilize the existing blank spaces in the fuse block, it is a fairly simple task to make a new circuit. One would need to:
1) Tap power from the main bus bar, and whack a fuse in there to suit the expected load
2) Run a wire from the other side of the fuse (on the under side of the fuse block)...
3)...and connect said wire (step 2) into terminal 30 of a SPST (single pole, single throw) relay. Ensure the relay is rated to handle the current of the circuit (higher than the fuse you installed in step 1). Think of a relay as an automatic, electronic switch- when a small circuit gets a little bit of power, it will active a bigger circuit that will run the power hungry stuff you connect to it.
3a) connect the load (ie the IGN wire of the engine saver) to terminal 87 of the relay - the earth of the engine saver device will complete the high current circuit of the relay
3b) Tap into a IGN source within the fuse block - this can be done with a *gasp* scotch block, or ideally spliced into a signal wire and soldered. Connect this wire to terminal 85 of the relay (this is the trigger, and will only draw a small current (approx 0.15A) from that circuit to 'close' the relay). Finding this signal wire may take some hunting with a multimeter to find, but will show 0V with the key off, and 12V when the vehicle is keyed on. Usually the fuse diagram on the lid of the driver's seat box will give you some clues- think about what accessories don't work when the key is off... cigarette lighter, headlights, radio, wipers, etc.
3c) Terminal 86 of the relay goes to ground, and completed the signal circuit of the relay.
Depending on the level of execution, what you've actually done is create a new circuit which provides power to the engine saver only when an ignition signal is present (ie vehicle key is set to accessories or ON).... and it would look almost factory in appearance.
All the space you could want is within that fuse block, it's just a matter of sourcing some fancy land rover / Jaguar relays to look the part!
What I've done in my ex box build is just this, but on a scale that will handle 100A for a range of accessories. This sort of current needs to be transacted outside of the factory fuse block though... but it's the same in principle.
Like I said, doing it this way is not the easiest, nor is it the most practical but as a thought exercise, it definitely is possible! Reasons for doing it this way may just be for a 'stealth' install, or because of space limitations, or aversion to random wires getting in the way. When you build your own circuit, you've designed it to handle the applications which you need it for- so you don't run the risk of drawing too much power thru a factory circuit, and causing electrical fires, shorts, or breeding gremlins. Plus you'll not need to top your land Rover back up with Lucas replacement wiring harness smoke. That **** is costly. :p
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