What is the switch responsible for shutting down power to the battery? I believe that I have a short in the ignition (believe me, a Saint would find his Dark Side trying to figure out electrical problems) and in trying to trace the fault I notice that turning the Key (Starter) Switch to the 'III' position kills all current to the battery. What is responsible for killing power from the battery? From my experience in rewiring a 35 curcuit classic truck, I would expect to fry the battery cable when I turn the key if it shorts...I don't expect to lose all power. I've got the 40 dollar electrical service manual but I don't even know where to begin researching what has been happening. Please help me before I begin to transfer my long-standing frustration to my subordinates...I simply can't take this much longer.
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1993 Volvo 940

What are the symptoms?

Battery going dead, battery OK but won't crank,.............?
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'96 965, 16' wheels, Michelin Pilot Sports, rear 18mm bar + Koni, 204HP cams, 126K. Put 200K on '85 745 TD.

To start with power does not go "to" the battery it comes from it so there is no switch per se that inhibits the current flow to the battery. The closest thing you will find is the ignition contact plate adn all it does is distributes current flow FROM the battery to where it needs to go.

Maybe you should start with what your problem is or just what it is that you are trying to acheive and then we'd have a better idea of which diagnostic direction to go in.

Mark

I'm confused, too.

I know that the electro-mechanical portion of the switch will shut off all power to all ancillary devices when in KPIII, such that nothing takes away from the available juice and the starter gets everything. I also know these switches go bad more often than anyone would like.

but yeah, if we know more, we can help more.
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'73 142, '75 242, '75 245, '80 245, '86 244, '87 745T

Sorry Guys-I was trying to write and sleep at the same time.

I've had an electrical glitch for a while with mostly nuisance symptoms. In my "Electrical Gremlin" post last week I explained details about replacing the key (starter) switch for the second time with a new one. Each time the new one was installed and the key was turned to KPIII, electrical power from the battery was terminated while the wires were still attached to the posts. This leads me to believe that there is some sort of safety switch inline between battery/key/starter to prevent burning up components. I've inspected the circuitry beneath the shifter and shifter knob and nothing appears to be awry.

What I just don't get at all is the fact that I used to be able to put the original key switch back on and it would start the car as usual, but put a new one on and it does what I have just described. Any ideas or advice?
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1993 Volvo 940

"Each time the new one was installed and the key was turned to KPIII, electrical power from the battery was terminated while the wires were still attached to the posts."

Exactly what are the symptoms that lead you to believe battery power is being "terminated"? Evan explained how, in KP III, power to all ancillaries is temporarily blocked off while the switch is in cranking position III . There is no "inline switch" that does what you suggest — other than that switch function.

However, if something is preventing starter operation, it would be normal for the lights and radio, etc. go dead when the key is in the cranking position. Is that what's happening? If so, it sounds like a possible starter (or control circuit) problem.
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Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.

CJ's post describes better than I did what is happening. I can hear the starter solenoid engage and then nothing-no electrical power to any electrical components in any position. The funny thing is that I've had dielectric grease on the battery terminals for years...its the only way I found to keep them from corroding over the span of a month. The battery is less than a year old.

It does help me very much though to know that there isn't an inline switch designed to power down the system as a protective feature. However, according to the Wiring Service Manual there is a "Start Inhibit Switch" located beneath the shifter knob. It looks like the switch has to be closed to complete the circuit and I'm assuming that it is like a "Neutral Safety Switch" on manual transmission vehicles that prevents the vehicle from being started when it is in gear.

One thing I don't understand at all though is why the old key switch, when reinstalled, started the car as usual and the new ones wouldn't. Does anyone else think that is odd or can it be explained logically?
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1993 Volvo 940

One thing I don't understand at all though is why the old key switch, when reinstalled, started the car as usual and the new ones wouldn't. Does anyone else think that is odd or can it be explained logically?

Sure. We all want to assume a NEW part is a GOOD part. Been through that too many times.
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'73 142, '75 242, '75 245, '80 245, '86 244, '87 745T

My reaction the first time that I put in a new ScanTech switch was that I had been sent a bad part, but the second OEM switch also performed the same way. This indicated to me that the problem was in my wiring. While it is still possible that the second replacement switch is no good either, I wouldn't think that it is likely. I don't know though...
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1993 Volvo 940

I've had symptoms similar to what I THINK he's trying to describe - turn to KPIII and there's not only no starter, but also no power at all, to anything, when key goes back to KPII. The problem was, it turned out, a poor connection at a battery terminal which would make just enough contact to power up the lights & radio but I suspect that the draw from the starter caused enough heat through the corrosion to generate a pile of resistance - until it cooled a few moments later, and lights/radio would come back. Pulled off the terminal, cleaned it up & applied some dielectric grease, no further problems. Start with the basics.
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Chris, Dartmouth NS Canada 70 M-B 280SE, 83 245DL, 84 244 turbo, 90 780 turbo, 92 VW Golf, 90 740 Rex/Regina

Try to start the car a couple of times then go out to the battery and see if either terminal is warm or hot to the touch; if it is, that indicates a high resistance to electron flow and there is a good chance that cleaning the posts and terminals will fix the problem.