"remote" battery "kill" switch for Volvo 240

Hi, especially to the Volvo owners,

We have a 1992 Volvo 240 Wagon - with a mysterious battery draining problem. When done driving and car is parked, its battery is slowly draining,
that far that when the car is parked overnight, the next morning the battery is so dead that even the lights in the dash stay off when turning the key.
Replaced the battery with two parts store bought ones as well as with one brought and installed by AAA. So I highly doubt it is the battery itsself.
Alternator charges it during driving, too.
Took it to my go-to-guy mechanic who pulled out fuses, relays, radio, lightbulbs to see if the charge stays - but nope, something’s still eating up
the battery charge when the car is not running.

I trust my guy and his opinion about being a waste of money to take it some other place which will do the exact same thing and mostlikely not find out
neither what’s going on here.
He’s right when he says that the battery charge stays fine if disconnect a terminal and later reconnect. But I think it’s a hassle to go somewhere, pop hood open, remove cable and then do same procedure when done with grocery shopping. My guy now said that he heard about something called “kill switches” that let you turn off the battery remotely without having to open the hood but also said he needs to do research about it as he hasn’t ordered/installed one yet.

I offered to look for something like that, too but realized that I’m bit lost and need guidance. Found some on Amazon out of all places that are toggle switches but they seem to be installed in the engine room under the hood - not that what we are looking for.

Anyone out there who happens to have had the same problem and found a solution? Installed a kill switch?

Thanks for sharing your experiences and thoughts

  • Markus

It sounds like something like a relay is staying turned on and suppling power to something until the terminal you mentioned is disconnected and reconnected, killing the problem. It would be nice to know what terminal he is disconnecting to clear the problem. I suspect it may be the power lead from the battery to the power panel under the hood, which supplies power to basically everything in the car except the starter motor.

To see how much current is being drained a current meter will need to be used at the battery. By keeping the meter leads in contact with the battery post and cable connector while disconnecting them it will keep current flowing so the trouble won’t go away when the battery is disconnected, then fuses can be pulled one at a time to help locate the problem circuit. I suspect the problem is located under the hood but it might be in the dash area.

If your friend has pulled out all the fuses and the battery still drains, there really are only two parts of the car left that is still hooked up to the battery: the starter and the alternator. One of them must cause some parasitic drain on the battery - after all: there’s nothing else to disconnect. All fuses have been out and all other components are fused or have a thermal link.

I’d disconnect each, one at a time, before leaving the car sit there to see which component is causing your trouble. If you disconnect the alternator and the car has a good battery in the morning, replace the alternator - do the same to the starter. Alternatively, you could pull out all fuses and then disconnect each (ie starter and alternator), reconnect the battery with a current meter in series to see what’s going on. Don’t start the car, though because most cheap meters won’t be able to deal with the current going through it under that condition. With all fuses pulled and just the starter and alternator in circuit, you should not see any current drain. Since your car is not working right, you may see a drain that could be measured with a regular cheap multimeter set to current.

A kill switch would have to be a really beefy relay, if it turned off ALL components being fed by the battery. That’s hack that won’t work for long.

Thanks for the responses so far… I’ll pass along this information to my mechanic (he’s the one who did all the work sofar and will do more on my car in future) as even though he said he checked everything, I’ll see if that included your suggestions. Am sure he got the right tools and measuring instruments. …amateur me thought that a kill switch is like a switch that you can just integrate in the connector cable and flip on/off like with a lamp :wink:

Rather than grope around with wiring for a long period of time, the next best move is to buy or borrow a factory wiring schematic and sort it out that way.

This is what you are talking about for $135.


Really though with a drain that big, it should be easy to find with a test light and start disconnecting branch cables until the light goes out.

I think rather than a cut off switch, you should find out where the problem really lies. If it’s a direct worn-wire type of short, it could eventually get worse until an electrical fire starts. In the meantime, if you’re parking it in the garage, I’d consider leaving it outside until the problem is found.

“I trust my guy and his opinion about being a waste of money to take it some other place which will do the exact same thing”

I think your mechanic friend is in over his head.
There’s somebody out there who understands this better than him and won’t “do the exact same thing”.

Yep, SOMETHING is causing the drain. The mechanic just hasn’t found it. So, ‘I can’t figure it out, so nobody else can’ reaction.

@Hasen - find a shop that specializes in auto electrical systems, they should be able to figure it out.

Whatever is draining the battery can easily be discovered. Any qualified auto-electric mechanic will be happy to sus it out for you. It’s just a matter of going through the circuits one by one. I’m not saying fixing the problem will be easy and inexpensive, but, knock on wood, even that might be true.

My first guess based on the symptom is that there is something wrong with the alternator. Either a diode has shorted out, or there’s a coil shorting to another. Did this happen soon after you had this car jump started, or jump started another car with yours? Jump starting is a common cause for this. You might try temporarily disconnecting the alternator connector and see if that helps the overnight battery drain problem.

If it’s not that, my second guess would be the starter motor. You could disconnect both wires ( a thick one and a thin one) going to the starter motor to decide one way or the other. Best of luck.

One caution: If you are not familiar with working on the electrical system yourself, best to have someone experienced in the loop before doing anything. I always remove the battery negative ground before connecting, disconnecting, or otherwise working on any part in my Corolla’s electrical system. Failure to do this could damage the ECM or even cause a fire. But on newer cars there are problems with removing the battery ground too. So like I say, it is best to have some help from somebody knowledgable, just don’t go mucking about by yourself.

Look on sites for boats. Boats have all kinds of electrical options. For cars I seem to remember one that went through the fender but that makes the car look kind of foolish.

You might look into a master switch system as used in general aviation aircraft. Basically it is a solenoid relay that connects the battery B+ to the electrical system with the activation of a toggle switch. For example in a Cessna 172 there is a master switch and a avionics switch. Activating the master toggle connects the battery to the positive bus. Now you can start the O360. Once the engine is running you turn on the avionics switch. This procedure spares the avionics from voltage spikes developed by the starter motor.

I have not looked at the specific ampacities of the master isolation solenoid but I suspect is quite capable of handling the starter current of a Volvo 240. The draw of the master solenoid coil is not that much so it would not affect the battery charging and accessory load handling ability of the alternator. The system isn’t hard to wire up. Just don’t forget to turn the master switch ‘off’ as you will drain the battery. Leaving the master ‘on’ after deplaning is a definite ‘nono’ (and costly) when renting aircraft.

Let us know what you find in your hunt for a cutoff device/system.

Whole bunch of battery switches at Autozone:


Some of our fleet’s truck use these

This is MASSIVE OVERKILL . . . but these things work


soooo a month later and $250 spent my battery seems to be keeping its charge.
Got distracted by some stuff like work but also did some research for a local mechanic that specializes on electrical stuff.

I didn’t get the full scoop (not sure if I would have understood) but after diagnosis the pinpoint went towards the wiring behind the glovebox compartment. I went down in the total dark before but didn’t see any light coming through any gaps - but still, whatever the mechanic did, I have been driving the car off and on, kept it parked overnight as one usually does and I did before and had no issues starting it up again.

Now I have to tend to another issue though as it seems something else is still happening from that part of the car - the good old sound that goes up with speed but gets low when no longer pressing the gas or stepping on the break (initial research shows it may be the fuel pump or fuel pump relay , the latter I replaced but its still coming up)

Oh well, one thing at a time I say

Thanks to all of you who educated me, made me want to pimp my car with an aviation or naval part …but in the end, I took the slightly more expensive way out that is more appropriate to begin with.

Until next time!



Look at the positive cables from the battery, it is possible wear on a cables sheathing is creating a short to ground.