KILL SWITCH, AGAIN

#81

Some of you may need clarification on this also(No offense). A 2 pole switch can switch 2 circuits. A double pole single throw switch has 4 terminals and turns 2 circuits off and on simultaneously. This is what you need.

#82

Instead of splice, I should have said cut/slice.
I plan to cut each of the two wires (in the passenger footwell area) and run each of them in and out of the kill switch (then back to sliced wires which lead to the battery).

The switch has 4 terminals so that it can switch two separate cicuits, and it has one switch throw.

Again, tell me if this will not work.

Someone had told me I needed to find the live alternator circuit under the hood and cut that so that it ran through the switch, but I’m thinking that just interrupting the big and little wires that go to the battery will do the trick and kill all power.

Thanks!

#83

And Mr. Levie,
The fuse that is on the little wire to the battery in the trunk is an 80amp in some sort of plastic case that says schlose?(definitely not stock or in shrink wrap; previous owner or builder must have installed it). Seems like it would not be doing anything after I turn the kill switch off, but maybe this is true no matter where it is…

#84

What you are contemplating will work. It isn’t necessary to run a wire to the alternator on an E30. The alternator output connects to main lug on the starter, which goes directly to the the large cable. The DME is powered by the small cable from the battery. So if you interrupt both wires from the battery and those wires aren’t tied together between the switch and the power block in the engine bay (stock they are separate circuits) the engine will shut off when the kill switch is turned off because the DME will lose power.

To avoid electrical transients when the kill switch is turned off it is a good idea to provide a resistance ground path from the large terminal of the kill switch on the engine side to ground via the NC contacts. That can be done by connecting a high wattage resistor from the large engine side terminal of the kill switch to a NC contact and connecting the other side of the NC contacts to ground. I don’t know if this is true of all suppliers of kill switches, but the three pole switches sold by Bimmerworld are suppled with a suitable resistor.

I don’t know what the rating of the OE fusible link would be and it has been covered in shrink wrap on every E30 I’ve ever seen. You may have an aftermarket replacement. So far as I know, a 60a fuse is sufficient. I place a lug type fuse at the power block in the engine bay in-line with the smaller wire. With the kill switch off the fuse does nothing as power is interrupted between the engine bay and the battery. So it matters not where the fuse is.

#85

Thanks, this helps alot, but your answer leads me to other questions:
-What is a NC contact?
-I didn’t get a resistor with my longacre double pole single throw switch, so I’m probably going to skip this because I do not really understand how or what to do. What sort of damage can these electrical transients cause?

#86

See page 4 of this thread for explanation.

#87

So if I were to put my kill switch on the cage at the passenger window, I would want to run new welding cable from the switch to the battery in the rear. Would #2 welding cable be a large enough diameter? That’s all I can get today and I think the stock battery cable is larger. I also can’t help but feel the stock battery cable size is overkill.

#88

#2 welding cable will okay for that run.

#89

So I wired my kill switch per the diagram on this page (without the option)

http://spece30.com/component/option,com_kunena/Itemid,94/func,view/id,49061/catid,9/limit,10/limitstart,20/

Car won’t start? Check! Cuts car off? Not!

Switch is a 2 pole Long Acre. I’ll check the smaller terminals to see if they’re NC or NO.

#90

Both contacts are NC - which makes sense to me.

#91

And just to complete the big picture, here’s the T-Block connections…

#92

And here’s the routing to/from the switch…

Soooo, it escapes me why the Kill Switch won’t kill the car (rather it’s killing me!)

#93

I think there is still a connection at the T-block that completes the circuit. The little wires and the big wires are connected there and back feed to the alternator.

#94

Diagram?

#95

It is a little tough to tell from the picture, but it looks to me like the DME power cable is on the wrong place at the power block. That cable from the engine harness should be connected where the small wire from the battery terminates at the power block. It looks to be connected to a lug on the main battery connection. That would explain why the engine won’t shut off.

#96

Here’s a Better close up of the junction block.

#97

All right! Now the Kill Switch kills!

Thanks guys!

#98

Follow up kill switch question.

We are mounting it right where the old junction block went and going to use a remote pull. Where does one find a ring terminal big enough to go around the main battery cable? The ones at the local auto part stores are not big enough on the wire side, however they are fine for the actual ring size to connect to the switch.

#99

A welding supply house can furnish lugs of the correct size for the cable.

#100

As will most aftermarket racing supply places (i.e. Summit, Pegasus, etc). The difficulty I have found is making a secure crimp on those big things. Make sure however you do it the connection is secure. We had one work loose on a buddy’s car months after he originally thought he made a good crimp on it.