14 replies to this topic

[stardude]

hiya

i will be fitting a start button and a kill switch soon, and was wondering how to wire up the kill switch?

should i put a switch on the positive side of the coil? or put a switch to earth the negative side?

thanks in advance

adam

[dklawson]

Always put the kill switch on the "points" side of the coil. For late model negative earth cars, that means coil (-).

What you're trying to do is mimic the points always being closed.

If you accidentally put the kill switch on coil (+), you will have melted wires before you know what's happening.

[Brams96]

Personally I would put it on the + side as thats the way your every day lights are wired and it is safer in the event of a fault. Also if you have to change the coil there is no voltage at the terminals once the switch is off.

You could always use the switch on the primary side of a 12V relay and switch both + & -.

Read this for a better explanation or do a google search for ignition kill switch, there's plenty of info out there.

Edited by Brams96, 18 October 2008 - 10:08 PM.

[dklawson]

Personally I would put it on the + side as thats the way your every day lights are wired and it is safer in the event of a fault.

For clarity as others read this thread I'd like to add a little bit of additional information.

There are many different items and methods described as kill switches. The aim of all is to disable something that makes the car/engine "go".
What I described is a traditional kill switch like you have on a lawn mower or some small motorcycles. It is a path to ground/earth that parallels the points. When it's closed, it's like the points aren't opening so you get no spark.
What I believe Brams96 is describing are switches put in series with the power to or from the coil. When these switches are "open" there is no current flowing through the coil and you get no spark.
There are also switches that "kill" the starter motor by interrupting the power to the solenoid.
Where an electric fuel pump is fitted, you can interrupt power to the pump so after a short drive the car runs out of fuel.
On race cars there are often main power kill switches that separate the battery from the car's main wiring.

Is one safer than another? I think it all depends on what your goal is and proper application. In this case... since you are planning on a push button start... maybe you do want to interrupt the power to the coil as Brams96 suggests so you don't accidentally leave the power to the coil on.

Edited by dklawson, 18 October 2008 - 10:47 PM.

[stardude]

so i could either put a switch in series going to the ing to the (+) side of the coil? and when its off, no power can go to the coil?

or i could put a switch on the (-) side of it with an earth?

i am guessing it would just be easier to put it on the positive side to cut the power to the coil?

cheers

adam

[dklawson]

Sorry, I was a bit unclear in my concluding paragraph.

As Brams96 suggested, putting the interrupter switch in series with the power to coil (+) will both kill the ignition/engine, and remove all power from the coil. Since you're talking about installing a push-button starter, the kill switch in series with the coil power makes a lot of sense from a safety standpoint.

A kill switch between coil (-) and earth has long been a standard feature on small engines and as a theft deterrent. It's actually easier to install (from a wiring standpoint) but can leave the coil powered up if you forget to turn off the ignition switch. That's why I think in Brams96 has got a better suggestion for your application.

[stardude]

ahh that makes it a lot clearer, thanks DK!

would i have to use a relay to do it?

or will a 20A toggle switch do the job?

cheers

adam

[dklawson]

The coil will only draw about 4 Amps when powered continuously. However, the DC current ratings of switches are much lower than their AC ratings. Make sure whatever switch you buy exceeds about 10 Amps DC and you should be fine. You can use a relay if you want. It's entirely up to you.

[stardude]

cool cheers for that, i have a great 20A DC DPDT toggle switch for the job.

cheers dk

[stormintrooper]

dnt see why u'd neeed dpdt, surely a spst would do?

[dklawson]

dnt see why u'd neeed dpdt, surely a spst would do?

Well... if you already have the DPDT switch....

Something you may wish to consider is using the other half of the switch for an indicator lamp to show when the ignition is turned "on".

[stardude]

dnt see why u'd neeed dpdt, surely a spst would do?

for the same reason DK has just suggested, to wire up an indicator lamp, to tell me when its on or off

[stormintrooper]

dnt see why u'd neeed dpdt, surely a spst would do?

for the same reason DK has just suggested, to wire up an indicator lamp, to tell me when its on or off

nice lol maybe one of MARK LCS (i think thats his name) does latching push buttons that illuminate

might be a nice touch iv certainly ben thinking about it

[stardude]

im planning to use one of his buttons for my start button

[stormintrooper]

nice one, maybe one for starter and one for immobiliser, either side of steering collumn maybe?