Battery disconnect switch...what gauge wire?

[Kyle K]

Hey folks, have a question I hope you can help with. I want to install a master disconnect switch in my '73 Blazer for 1) security deterrent and 2) easy electrical turn-off as I continue to do work on the truck (I'd normally remove terminal). For these two reasons, I'm not going down the solenoid route, but rather a simple two-post switch.

https://www.jegs.com/i/JEGS/555/10307/10002/-1

I went heavy duty with 300 amps just so there wouldn't be any issue starting a new SBC 350 (from reading other articles).

So my question...what gauge wire should I use? I've heard a lot of people recommend welding wire. And I've looked at charts and such about amperage which makes it seems like I need 2/0 (but that seems like overkill). Would a normal 2-gauge wire work? I plan to run the switch somewhere behind the firewall, so for easy math assume 6 ft from battery to switch, then 4 feet from switch to starter.

I've love any help you can offer (I'm just learning electrical stuff now). Also, please correct any of my assumptions if I was wrong.

Thanks!

Kyle

 

[C10MixMaster]

2 gauge will be fine I do like welding cable because it is finer strands = better conducting. but any 2 gauge should be fine.

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[AuroraGirl]

2 gauge would do the trick. Where at do you think youre gonna access it from? by pedals?

 

[Snoots]

2 AWG welding wire will do nicely.

Add a 3 AMP fuse across the terminals of the switch so that clock/radio will not lose their memory.
It'll blow if someone tries to start it.

 

[82sbshortbed]

I'll blow if someone tries to start it

Will you now?

 

[AuroraGirl]

Will you now?

We dont keep him around here for nothing

 

[Matt69olds]

Welding cable insulation doesn’t hold up well with oil. Just something to keep in mind.

If you use a Ford starter solenoid, you could put your electrical cut-off switch on the 10 gauge wires coming off the factory solenoid. Use the other terminal on the switch to supply power to the fuse box. The cutoff switch would see at most probably 60-70 amps, you could run much smaller wire, and the battery cable running down to the starter isn’t powered unless the engine is cranking.


This is the method I use when wiring a race car with a trunk mounted battery. I don’t like the idea of a 2 gauge or larger wire running from thr back of the car to the front that is electrically live whenever the switch is closed. The only downside is you need to run the output wire of the alternator to the BATTERY side of the cutoff switch. If not, the engine will keep running with the switch off.

 

[Snoots]

Will you now?

Damn auto-correct! It'll !

 

[Kyle K]

Thanks all for the info, that helps out. And hilarious auto-correct.

 

[Matt69olds]

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[F-64]

Prowire has motorsport battery cable.
https://prowireusa.com//c-20-battery-cable.aspx

Depending on where you locate your switch you may need a water-resistant switch. I've had one go bad because of corrosion.

Crunch the numbers on voltage drop. 2awg may be bit small for 10' at 300amps. I would go with 2/0awg
https://www.wirebarn.com/Wire-Calculator-_ep_41.html

Also, be careful the terminals on the switch can't short to ground or wiring get pinched. Unless you decide to fuse the line close to the battery.
I've set a car on fire because of this.

 

[WebMonkey]

i'd just remote a high amperage latching relay and call it done.

wouldn't have to worry about what gauge wire etc etc.

you could even 'toggle' the relay from a 9v battery if you didn't want to run the relay actuation power from the vehicle battery.

good luck!

 

[Snoots]

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[MikeB]

I don't like the idea of adding 6 ft of cable, regardless of gauge, between battery and starter. It also means two more connections and a pair of switch contacts to add resistance to the circuit, or downright fail. Especially if it's Chinese-made. If you do add a switch, I'd first talk to the "manufacturers" about who makes their switches and where.