Safe Battery Wiring

[Hindsight]

I've been spending a lot of time trying to come up with a very safe way of wiring up the battery, fuse box, alternator, and starter. Something that ensures all components are protected in the event of a short, and to prevent fire and other damage.

I am running both of the fuse-boxes up-front under the dash. This means I have to extend the wires to the alternator, but I can shorten a lot of other wires.

What bothers me is having one or more long, heavy gauge wires that could cause a fire if shorted. So I came up with one solution. I'm sure there are many ways to attack this but the diagram below shows my idea.

I didn't want a fuse on the main wire to the starter (lots of amps and is not generally something automakers will do). So instead, I added a starter solenoid attached to the front firewall. This ensures that the large gauge wire to the starter is not live except when cranking the engine. It isn't shown in the diagram, but the trigger wire that normally goes to the starter would go to the third terminal on the remote solenoid, and you could just bypass the solenoid on the starter by permanently attaching a jumper wire with ring terminals.

The alternator has a fuse on the engine-side of the firewall to protect from grounding in the engine compartment (especially if the battery positive lead becomes disconnected for some reason). The OEM fusebox has a 120 amp fuse between the battery feed wire and the alternator wires, so protection remains in place with this setup for any surges or shorts.

You could run an additional ground to the engine block, or just do as FFR suggestions which is ground the battery to the frame and run a strap from the frame to the engine. These aren't shown in the pic below but you get the idea.

Curious to see what others think of this, and have done to ensure shorts or surges don't start a fire or damage sensitive electrical components.

http://i.imgur.com/RWv6us3h.png (http://imgur.com/RWv6us3)

[STiPWRD]

The intermediate starter solenoid seems a bit overkill IMO. If you properly wrap that wire with loom, secure it throughout it's length, and use rubber grommets at wall pass-thrus, there should be a very low risk of it shorting throughout the life of the vehicle or in the event of a crash. But if you feel you need it, it shouldn't hurt anything, I just wouldn't personally. My starter wire goes through the center tunnel so it's away from most crash impact areas.

[Hindsight]

Thanks for the reply. I agree that it's low risk, but my concern is that the stakes are high. If something does short out, that giant wire with full battery amperage is going to very likely burn the car to the ground. Having that big starter wire going under the intake manifold seems sketchy.

[RM1SepEx]

Thanks for the reply. I agree that it's low risk, but my concern is that the stakes are high. If something does short out, that giant wire with full battery amperage is going to very likely burn the car to the ground. Having that big starter wire going under the intake manifold seems sketchy.

run it around the engine vs under the manifold

[michael everson]

I make a habit of covering my positive battery cable in either heater hose or something similar. I do this on all my builds. Especially in the cobra where something could hit it from under the car in nick the covering. Cheap and easy.
Mike

[Hindsight]

That sounds like a good and inexpensive safety feature. What happens if something grounds the terminal on the starter or alternator?

[RM1SepEx]

those connections need to have thick rubber covers... My cables going around the motor are in sheathes as well

[longislandwrx]

just insulate it well. people run 8/4/etc gauge wire to their stereo amplifiers all the time and rarely you hear about a car burning down.

I think you are being slightly paranoid

[Junty]

Thanks for raising the awareness in this thread. I personally agree that good insulation is essential, however in addition to this and to not necessarily prevent fire but to save my Motec ECU in the event of an accidental short - here is what I did...
Before the battery cable passes through front firewall (about 1 1/2foot) cable - I connected a dual circuit isolation fuse. I wish I was near the car to give exact details, but I vaguely remember that it has the battery input cable - then two separate isolation circuits - one 60amp the other 40amp. I used the 60amp to run through the centre tunnel to the starter, and the 40 amp runs to the fuse box and all the cars electrics.
When mounting the isolation (fuse) - this is an electronic version, has a reset button on each of the two circuits. I attached it to the firewall with a small cutout so that the reset switches are accessible from the passenger foot wheel inside the car.
In addition to this isolation, good insulation wrap through the centre tunnel and rubber grommets where ever there is cable passing through the firewalls. This maybe a little more than is necessary - however it is save, ensures accidental shorting of any circuit will not damage my ECU, and unlike standard fuses reset is a simple button press.
IMO covers everything...

[Zach34]

I think that's a smart idea. The entire reason I got my donor was because of a 4ga wire short that resulted in a massive interior fire. The 4ga wire had a 100 amp fuse installed near the battery. The car was stolen and when the thieves cut the power wire to the amp in the trunk, they let it flop on the carpet. It shorted through the thin fabric on the back of the rear seat and set the seat on fire. The fuse never blew, and there was no visible damage to the 4ga wire.

Of course, we don't have a lot of carpet or flammable material in the car, and you could argue if the wire shorted directly to the frame instead of through the carpet, the amperage might have been enough to blow the fuse. Still 100 amps is A LOT, plenty to cause a very hot spark before the fuse blows.

[Hindsight]

Yeah that's the kind of story that scares me. I am definitely leaning on the side of caution here, but after all the time and money I am spending on this build, anything within reason I can do to keep it from going up in flames is worth it to me.

If you mount your main power relay box in the front, then your alternator wires aren't going to be long enough. What I previously did was to simply connect the alternator to the starter; this way they were on the same line going to the battery which also connects to the main fuse box up front. Allows you to have only large gauge wire going from back to front. The only issue with this is that it negates the factory 120 amp fuse that separates the alternator from the battery. What happens if the alternator surges or fails in a way that shorts to ground? You have no fuse protection from that if your starter wire is connected to your alternator wire, and of course, no insulation will prevent a fire in that situation. The diagram above solves those issues.

[BN]

i can not remeber what it call but at canadien tire store in canada put it on the pos side ,it protec from very hight amps also if you forget your lights it well trun off before battery goes deed