8 replies to this topic

[mike.]

My car has quite a few extra accessories running from the standard fuse box and a couple running straight from the starter solenoid.

At the moment i'm doing a bit of rewiring and making a new loom for my megajolt system and i'm considering putting in a second fuse box to run the extras.

The sort of stuff i'll have running off it is the megajolt (which includes the MJ unit, the coil and the EDIS module) my radio, fuel pump and my spotlights; so a fair few bits that must put a fair bit of extra strain if I wire them all into the standard fuse box.

I'm thinking of getting a fuse box like this: Link - A 6 way blade fuse box.

I was thinking this would be easy to wire by running a large gauge cable from the starter solenoid and splicing it into 6 smaller 20 amp or so wires to each fuse and then I can just power whatever I want from the second fuse box. However most of the accessories i'll only want powered when the ignition is on - Especially the fuel pump and MJ.

So what would be the best way of wiring in a new fuse box that works from the ignition but still is safe enough to have 4-5 accessories running off it?

I should add that wiring is exactly my strongest point either!

Thanks

[rustandoil]

Use a relay that is energised only when the ignition is live (a white wire on you existing fuse box) and have your "large gauge cable" wired across the contacts of the relay, might be an idea to have a high power fuse to protect your new circuits, try Vehicle Wiring Products, not necessarily the cheapest but most of this stock is good quality and quick delivery


edited because lrostoke was correct with wire colour

Edited by rustandoil, 20 June 2011 - 12:12 PM.

[mike.]

I see, so the ignition just acts as a switch for the relay.

Since i'm going to have a fair few things going through the relay i'm going to need one of the high current ones right?

On vehicle wiring products they do high current ones - Pretty pricey at £20+ though. What sort of amp relay would be need to run things like 2 100w spotlamps, my megajolt ignition inc coil and EDIS, radio, fuel pump and then a couple more things possibly in the future?

They do a 100a one which has stud connections rather than spade connections which would be better to run a big cable through as I could crimp a big ring terminal on.

100 amp should be plenty right?

[lrostoke]

Why not just use 2 relays 40amp = 80amp total. More than enough

Split your fuse box into 2 sections, 3 fuses fed by each relay

So basically 2 seperate high ampage cables from solenoid battery terminal one to each relay .
energising side of relay takes power from ignition (white wire on standard fuse box)

Then each relay when switched send power to 3 terminals of additional 6 blade fuse box.

40amp relay about £2 each or free if you wander round local scrap yard and pop them in your pockets. Not that I condone such behaviour

The formulae you need know is I x V = W (amps x volts = watts)

to get ampage its watts / volts .... 200w / 12v = 17amp rounded up

Edited by lrostoke, 15 June 2011 - 09:57 AM.

[mike.]

Ok, thanks for that.

My spotlights are the biggest draw i'll be putting from the fuse box, so if 2 x 100w spotlights use 17amp, then this cable would be suitable right?

http://www.autospark...roducts_id=1010

3 cores, each core carries 17 amp (i'm assuming it means each core carries 17amp and its not 17amp for all 3)

This way it'll be pretty neat as I can have 2 larger cables which split into 6 12v feeds to the fuse box.

Any reason why that cable wouldn't be suitable for this use before I order some?

[lrostoke]

Just did a quick google and found this.

http://www.halfords....nstructions.pdf

Components Required (Supplied as fitting kit in certain packs)
17 amp cable for 2 x 55w bulbs; 27 amp cable for 2 x 100w bulbs
A fuse box or in-line fuse holder (15amp fuse for 2 x 55w bulbs;
25 amp fuse for 2 x 100w bulbs)
A switching relay (either 4 or 5 pin)

I tend to air on caution side and go a bit beefy with cables

Actually not a bad link that Halfords one, gives fitting and legal advice for aux lighting

Edited by lrostoke, 20 June 2011 - 12:27 PM.

[mike.]

Not a bad link at all considering its halfords!

If I stuck with 55w bulbs in my spots do you think that 17amp 3 core cable would be ok?

Only reason I was going for 100w was because I'm rewiring them and thought I may as well.

[lrostoke]

Can't see any problem with it, plenty of safety margin at 17amp

[mike.]

Cool, should make for a pretty tidy addition with the multi-core cable and relays hopefully.

Thanks again.