toggle switches to control fuel pumps and ignition

mickster8888 · 02-20-2010, 12:03 AM

i'm thinking about installing toggle switches to operate the ignition(electromitive hpv1) and fuel pumps in my 1983 930. where would i break the circuit for each component? the factory ignion switch would be left in order to operate lights, wipers as well as unlock the steering wheel. i'm also installing a battery shutoff switch and a solenoid to shutoff the alternator. which wire on the starter goes to the alternator that needs to be switched? any info would be greatly appreciated. drawings would be even better. thanks in advance.

lateapex911 · 02-20-2010, 02:03 AM

Question...why are you doing this? It's a typical racing mod, and the batt cutoff switches need to be wired in such a way as to shut off the car, and the alt, but NOT fry the alternator. There are usually diagrams that come with the switch. And a warning, the wiring isn't for a novice..it needs to be done properly with the proper gauge. The switches are notoriously unreliable. If you don't have a real need for it, don't install it.

mickster8888 · 02-20-2010, 12:35 PM

car is going to see track/street use. it's got a full cage, track suspension, and rides on hoosier r6's. 17x9 frt 17x12rr. i think you see where i'm going with this. i would like to go to toggles so if anybody has any ideas please let me know.

Walt Fricke · 02-21-2010, 06:57 PM

Mick

Do a search for "battery cutoff switch." This comes up frequently on the AutoX/Racing forum.

Go take a look at the PCA Club Race rulebook (you can find it through pca.org under club racing etc.) for a general location to mount the cutoff. Down in the trunk generally between the battery and the fuel pump relay, with a wire leading up through the back of the hood. When on the track, tape the loop on the end of the wire to the cowl. When driving around, poke the wire back into the trunk so no one can casually turn your car off.

The simplest and most common switch is the red keyed Merit. You want the one which not only has two big posts (for the battery) but also four small spade connectors, two for each of two internal switches. It comes with a wiring diagram.

You can purchase a short battery cable with a ring end. Run that from the positive to one of the big terminals.

What I did for the stock battery cable was to purchase a lead battery terminal - looks like the slightly conical terminal on top of a battery, but has a threaded hole in the wider end. This you can screw onto one of the big posts of the cutoff switch. The threads don't really match, but they are close enough and this is lead so things mush on nicely. This way you don't have to cut or in any way alter the stock cable.

One of these switches serves to turn off either your ignition or your fuel pump relay when the main switch is off. The other grounds the "cold" side of the battery cable through a resistor when the switch is off.

In your case, turning off the fuel pump relay through the relay control wire (low current) is the obvious way to go, as it is close at hand.

A good way to wire the HPV-1 is to run a thick wire from the starter/alternator/battery connection to a relay, and from the relay to the HPV-1. No voltage drop that way. And to control the relay with a low current connection from up front. Like the stock ignition wire.

No reason I can think of to take the stock ignition switch out of this system for a street/track car.

My ignition switch started acting up - sometimes would turn to the start position, sometimes would not. I installed a momentary on push switch in parallel with the start position, mounted it through the dash above the switch. If the key doesn't do the trick, push the button. Cheaper and easier than fussing with the guts of the key portion of the switch.

My 2 cents

Walt Fricke

mickster8888 · 02-22-2010, 02:08 PM

walt, thanks for the info. the hpv-1 is wired to the stater/alterator/battery connection on starter to a relay in the engine compartment to feed the hpv-1. i'm gonna install a toggle switch to interupt the hot from the ignition switch to turn off the hpv-1. as far as the fuel pumps, i'm gonna interupt the control wire to the red fuel pump relays to turn the pumps off with toggles. should i have a seperate switch for each pump? any help would be greatly appreciated.

Walt Fricke · 02-22-2010, 07:30 PM

Ah - I forgot, 930s have 2 pumps. If you are going to switch one, why not switch them both. I happen to like relays so switches don't have to carry much current, and wires from them don't have to be thick.

But for a battery cutoff switch also to stop the motor from running, you need to use it to disable either ignition or fuel pressure (for anything other than carbs) separately. Othewise the alternator current will just keep things running, even if the battery cable is only hot for a foot or so.

Venues which require a cutoff usually require that it stop the engine as well. PCA does. Hence the virtue of the cutoffs which incorporate those two extra switches. That system is independent of the various other controls we may want, though it could use their wires (running relay current through the proper small switch on the cutoff unit, for instance).

mickster8888 · 02-23-2010, 12:25 PM

walt, i'm using painless wiring products remote battery cutoff which is used in conjunction with their high amp alternator cutoff solenoid. basically when the batt shutoff solenoid is energized it also energizes a solenoid to disconnect the alternator as well. i'm in the process of wiring the switches to turn on/off the fuel pumps and ignition using toggles that interrupt the relay on the terminal that comes from the ignition switch. i believe it's terminal#86 on the red fuel pump relay.

Walt Fricke · 02-23-2010, 05:19 PM

Mick

My apologies. I am suffering from cognitive dissonance here. You have the big picture well in hand with fairly high end stuff - Painless, relays, etc. But your question sounded so basic that I misread your initial post.

The typical system does not separately disconnect the alternator from the positive power grid. Rather it cuts off the battery so crushed wires can't spark from that source, and disables some key component so the engine quits running even though the alternator is supplying power to the grid until the engine stops.

While I think using your system to disrupt ignition or fuel pumps would be simplest, the alternator connects to the battery at the starter. It is the thickish red wire with a ring end terminal on the same starter solenoid post with the cable from the battery. Easy to identify. Not as fat as the battery cable, but thicker (10mm) than any other wires in the neighborhood. Not a lot of slack in this wire, so I imagine you'd need to do some splicing to install a relay on it.

However, this is not the end of the story. There are at least two other wires from the alternator which have positive current on them and could be "sneak paths" for alternator current to the grid. And not only might they keep the engine going, they might overheat and fry trying to do so. Look at the wiring diagram and you can see that (for alternators with an internal regulator) the alternator D+ runs on a blue wire through the 14 pin relay and up front to the alternator idiot light. On some models, there is a diode between the light and the battery connection. On others it looks like there isn't, and I'd expect the bulb to burn out if this path is not interrupted.

Which might mean that each time someone tests the cutoff you blow the bulb which helps the alternator do its thing as well as warns you if the fan belt has come off and so on. So you'd need to replace this bulb.

There is also a larger red wire from the alternator B+ through the 14 pin relay to the relays in the engine bay, providing high amp power to the rear window defogger and engine heater blower motor. I don't think either of these could provide a sneak path, but you ought to verify that.

Cutting off either the 86 (positive) or 85 (ground) contact on the fuel pump relay solenoid will kill the fuel pump. Note that both of these terminals have two wires connected to them - the extras go to the rpm limiter. I think the relay socket will have a red wire which just loops from the 86 to the 87A (fused high amp positive) terminal, so if you pry the rubber socket out you could find, identify, and cut and splice your wires to your relay (or just your switch - this is a low current wire) into this. Alternatively you could interrupt the ground for the relay - the ground for the relay actually occurs back by the engine! It is part of the air flow sensor in the CIS system. You want to have a wiring diagram handy. Assuming your 930 wiring is not all that different from an 82 SC, Pelican has one and you want to be familiar with it.

Walt

mickster8888 · 02-26-2010, 06:42 PM

walt, i just tested the cutoff switch and with the engine running as soon as i hit the switch the whole car shuts down. this must mean i have taken the alternator out of the circuit as well as the ignition. all this being said, there is no way for me to fry the alternator/regulator with the engine immediately shutting down?

Walt Fricke · 02-26-2010, 08:28 PM

Mick

Well, before purchasing a multi-pole cutoff switch with instructions, it would not have occurred to me that cutting off the alternator positive might cause problems.

The situation presents itself like this: 1) your car is running, and you turn the engine off. During the time it takes for the engine (and alternator) to quit turning over,, the alternator is still pumping out amps/has a voltage potential. No problem, as the battery is right there to absorb it no matter what all else is shut off.

2) But if you stop the engine (by disabling a vital function like the ignition) and simultaneously open the alternator hot wire (whether at the battery or back by the alternator), so it isn't connected to the battery, that current/voltage has nowhere to go. It is suggested that this could "fry" a diode or diodes in the alternator. Hence the solution by the multi-pole cutoff switch folks - a 10 watt low Ohms resistor connecting the alternator to ground when the cutoff is actuated. That gives this mischievous electricity somewhere to go - to ground, but not instantaneously, so amps don't get too high.

I am not certain just what is going on here that could cause damage - a back EMF? - maybe a current spike similar to how a spark coil works, with a charged field collapsing?

It does occur to me that if you cut off the battery at the battery, and also cut off the ignition, then couldn't the fuel pump (if electrical, as most are) serve this function? Or the ignition if it is the fuel pump you disable to make the engine quit running?

So you now know as much (or little) as I do. I'm pretty good with Ohms law, but beyond that I have to be careful.

mickster8888 · 02-28-2010, 07:37 PM

walt, that was my thinking exactly. however, the high amp alternator shutoff solenoid has what i think is a diode on it. it is in between the positive and negitive post on the switch side of the solenoid. i didn't know what it was. am i wrong to think it is a diode for the purpose you explained? this solenoid is designed specifically to disconnect the alternator.