Fia Master Switch

[Snapperpaul]

Yet another ebay bargin arrived a couple of days ago in the form of a FIA approved master switch, used but in good working order.

Standard 8mm posts for the big red cables and two pairs of spade connectors.

First thiung i did was to put it on a meter and when switched the main poles are good and one set of spades connect, however the other paired set let current flow only when the switch is off???

Curious to know how these would be wired in and what for?.

What would you need that only came on when the switch is off? or do i sense some switch over relays and a bit more complicated wiring comming my way?

[Guest Tony Tank]

Would it not be for something that needs to be feed ie- a time piece that needs to keep running or on the kit your cd player etc.

Just a thought

[Snapperpaul]

Problem is that that pair of spade terminals ONLY flows power when the master switch is off, so no power while the car is run.ning

[Guest Tony Tank]

Could it be for an alarm system that is armed when you switch the master off

[Guest allenr03]

I think its something to do with the alternator and preventing damage to it when you switch the engine off. I'm sure I've read a thread on here before along similar lines.

[Guest Dan_Beeston]

Yep, these terminals are usually used to feed a high power resistor to dump power to ground. (At least that's what I've always used them for!)

 

When you throw the switch with the engine running the alternator is still spinning/charging but suddenly has no battery to sink charge into, which can cause the voltage to spike & damage the alternator or any electronics on the power net. Switching a big resitor (high power, low resistance) between the powernet & earth allows power to be dissapated (as heat) until the engine stops turning.........

[Snapperpaul]

Sounds like a plan Dan, will investicate further.

[Longboarder]

This was posted a while back. Can't remember who by but sorry for the theft of the pic whoever you are.

 

Nigel

[Snapperpaul]

Thank you very much Gentlemen, a solution found.

[baj25]

Paul,

I’ve got one of these as well, I’ve been waiting until after SVA to fit it. Where are you thinking of fitting it? I think it’s best to keep the main battery cables short, but the switch needs to be somewhere accessible which limits options. Brian

[Guest peter2b2002]

i fitted one of those to the near side of the dash, with the main switch ON the small connections are open, with the main switch OFF the small conections close dumping the alternator output to earth via the resistor, i haven't used the small connections on my set up as i have used a kill switch and push button start via relays

pete2b

[Snapperpaul]

baj25, not sure just yet, i think i will put it through the engine bay side or a cut out in the bonnet.

Needs to be away from the carbs as they can spit fuel out and as you say, keep the leads short.