Hi William Hechler,

You are describing in metaphor? Parking a car in the bushes o weeds or on grass or soil for some period can cause corrosion of both the electrics and the steel body. An FYI. So long as these parking surfaces drain including gravel, asphalt, concrete, or on these surfaces partially or fully covered will ensure a longer service of the automobile.

When working with automobile or low volt DC system connected to a battery, always disconnect mains, breaker, switches, and always remove the key from the ignition.

At any rate, how 'bout some wiring diagrams?

The Volvo 940 1991 Mitchell.pdf (Mitchell Repair Service) line-art wiring diagram marks the the battery cable as orange (or red) insulation for + positive and blue insulation for ― negative. There may black sheathing covering the battery cable insulation.

The negative cable, on inspection, connects to the body sheet metal and the engine block.

The positive connects to a power distribution block (right exhaust side rear of the engine bay and the starter motor solenoid.

http://www.v8volvo.se/mekartips/volvo/

Volvo 940 1991 Mitchell.pdf

I may be able to find the Volvo green or blue cover service manuals scanned to PDF for your 1991 (I'll guess) North American market 940. A low volt DC system such as that in an automobile has few safeguards should the user reverse battery polarity.

In doing so, and if smoke escapes, anticipate damage to electrical system components. Stuff that got hot and smokes as you describe. If circuits were not powered, you may be lucky. However, the fuel injection and ignition engine control systems receive B+ power at all times. Those circuits inside the ignition control systems usually have robust diodes on circuits boards that should prevent electricity flowing in the wrong direction. I say should. With the key in the ignition, and you note items getting hot and smoking, I worry.

With the wiring diagram, you can trace connected circuits that may have been damaged.

Also, you may want to search using Bing and Google for related incidence on similar era Volvos, VW, Saabs, BMW, where the owner connected the battery cables yet reversed polarity.

Hope that helps.

Sorry for the problems. I've done this once while jumping a battery. I blame the dyslexia. Yet was quick to disconnect. The key was not in the ignition. Was not a Volvo. Some sort of 1970s Ford. The Ford owner continuously distracted me. We were using another, more ancient, Ford, with a better battery, to bring the live battery to the dead one. This was in the mid-1980s or so.

Questions?

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Car makers need to install voltmeters on dash boards so we can tell instantly how much juice is alternator putting out. Having only red alternator idiot light does nothing except makes us panic, as at this point we know we are screwed.

The battery posts are different diameters. To reverse the connections you would have to spread the negative connector excessively to go on the positive post and not be able to tighten the bolt. The positive connector would be very loose on the negative post even when tightened as much as possible.
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Dear William Hechler,

Hope you're well. I'm puzzled as to how the battery cables could have beeen transposed. On a '93 940, there's not enough slack to enable the negative battery cable clamp to touch the battery's positive post. The cables are color coded: red for + and blue for - . Further, almost all batteries have the post designation (+ or -) molded into the plastic case.

The things "not working" receive power, when the ignition key is in the "accessory" position. Thus, the relay for the seat heaters may have been "fried". If the seats are powered, do they work properly?

In Volvo VADIS - a superseded dealer parts/service database - there appears to be a relay (marked "K", Volvo #1324749) which controls power flow to the headlights. That relay, too, may be "junk".

The radio may have its own protective fuse, that can be replaced.

If the car has central locking, that relay may also have been damaged.

Inspect the master window switch unit (driver's door).

The alternator - almost certainly made by Bosch - likely is "junk", unless a rebuilder has spare parts (diode bridge, capacitor, etc.).

In short, check all electrical items, and post your findings. Using the specific term - rather than "it" - makes clear the item, to which you refer.

Hope this helps.

Yours faithfully,

Spook