I’ve had an electrical problem for over a year now. It began with the SRS light staying on and “sapping” power (I know now that isn’t what was happening, but that is the way that it appeared) from the rest of the electrical system (see my "Penntellect" 1/13/2005 posting.) Now, it appears that the warning lights that are coming on are not “false alarms” but rather real problems related to the electrical system. For example, the Overdrive Indicator light comes on without my input, I can’t turn it off manually, and I can’t drive over 45MPH at 4000RPM. I’ve taken my ’93 940 to the dealership with this electrical issue, but they don’t want to do very much because they won’t guarantee they can fix it. I have run and cleared diagnostics on it more times than I care to say, but diagnostics really isn’t telling me anything (for instance, the ABS diagnostics tells me it is a crash sensor/dealer fix.)

The biggest piece of new information on this problem that I have (though I don’t know how to interpret it) is related to the key switch / ignition switch replacement. The dealer told me the last time that I took the car in to them that when they have seen this symptom before, they have replaced the key switch and that has been the remedy but they would not guarantee that would fix my problems. I have attempted to replace this starter switch with both a Scan-Tech replacement and an OEM replacement, and both of them seem to be shorting out (or triggering a shutdown switch?) the electrical system after I reconnect the battery and turn the key to Position iii-whatever it is, the car loses all electrical power once the key is turned.) After about five minutes of sitting there contemplating where I went wrong, the power mysteriously comes back on-but I can never crank the engine. When the old key switch is reinstalled, it starts just fine but I’m back to the same old problems.

Does anyone have any ideas of what I can check or what might be causing this? I’m thinking that some feature preventing this short/trigger on the old key switch must be burnt which isn’t on the new ones. I have replaced the Overvoltage relay (the fused relay which regulates voltage coming into the dash), but am beginning to think that this problem is in the ECU. Would any of you agree and think it worth investment in a new ECU?

I appreciate and look forward to your feedback!
--
1993 Volvo 940

There are a few basic things that you, or anyone else having electrical problems, can do to rule out the easy stuff before going after the tough ones.
Remove both battery cables and look very closely for corrosion and deterioration, especially at the smaller of the red wire/s ( sometimes there is a bundle of smaller red wires) at the positive terminal. Acid can corrode the connector terminals and creep up inside the wires making for high resistance( = lower voltage), unhappy and confused electrical devices. Do a voltage drop test on the big wires, both the pos and neg, if possible. If in doubt replace the wires. Take off and remove every ground wire connection you can find, clean ,replace and then seal with dielectric grease, especially the one at the alternator.
The OD problem could be another blinky relay that just needs to be re-soldered. Check the 700/900 FAQ for instructions, and other great info.
--
Gary Gilliam Sumerduck VA, '94 940 na Regina 150k, '86 240 180k

Dear penntellect,

Good a.m. and may this find you well. Using the 1993 940 wiring diagram (Volvo Manual TP32208/1), I'd guess the root problem is a weak ground. The change of ignition switches - and the persistence of the problem - suggests the problem is wiring-related. It is unlikely, that you got two faulty replacement ignition siwtches.

A weak ground could result from:
(a) corrosion
(b) a loose connection
(c) damaged insulation or a wire's conductor being broken inside the insulation (the result of the wire being pinched - or having been pinched - when it was caught between two hard objects).

Because there are several problems, there are several places to look. Ground points, for the instrument cluster and related items are:
(a) behind the kick panels on either side of the footwells, just in front of the point, where the front door hinges are attached. When removing the plastic panels, be gentle: plastic gets brittle with age.
(b) inside the engine bay, on the inner fender walls, just behind the headlights
(c) the main electrical distribution block (fuse block), which is behind the fronter center console ashtray.

Ground wires are usually black. Ground contacts can be cleaned with an aerosol de-oxidizer (available from auto supply stores).

You will need a volt-ohm-multimeter, to check for continuity (that the wire is not broken). Set it to "OHMS"( Ω ). You will need someone, to wiggle the wires, while you check them for continuity, so that if there's an break, the movement will reveal it. The meter should read "0" = no resistance, if the wire is in good condition. If the meter reads ∞ = infinitely high resistance, that means the wire is broken.

You could get lucky, and find:
(a) an obviously broken/loose/corroded ground wire
(b) a ground wire, that is pinched (look for indentations in the insulation).
A pinched wire should be replaced, unless you can wiggle it, and it shows no signs of being broken inside the insulation.

Hope this gets you started. Electrical problems require great perseverance. If you persevere, you'll find the fault.

Please post back, with your findings.

Yours faithfully,

spook

I made a serious mistake in trying to correct this problem last year by using Di-Electric grease which I squirted into the holes in the wiring harness which attaches to the key switch. Not understanding the contruction of the harness connector, I added too much and actually created a connection between several of the terminals inside this harness (back behind the plastic shroud.) In beginning my chase of possible faults, I noticed that the yellow wire which feeds into the harness showed mild signs of charring at the terminal point. I believe that the excess grease is to blame.

I cleaned off the excess grease and got the terminal connector block back together with the few extant diagrams for this part that I have been able to locate. However, I notice that the extant diagrams all seem to show the wires exiting the wrong side of the block - thus eroding my confidence that the diagram is correct. Has anyone else happened to rewire or replace this harness to be able to advise the proper configuration of these wires? Or short thereof, does anyone have a complete and thorough diagram of this harness?
--
1993 Volvo 940

Dear Pennetellect,

Good a.m. and may this find you well. The electrical diagram for the ignition switch is found on page 6,of the Volvo Technical Manual, noted in my post.

There is, in the center of the connector, a circle, with one side flattened. Above that, there is a groove, in the edge of the connector. As you face the connector, there are two openings, below the groove. The opening on the right side of the groove, should receive a Black Wire. Note - In the list below, there are two each of the following colors: Black, Pink, Red, and Blue/Yellow. This is not an error.

Moving clockwise, the wire colors are:
Pink, Yellow/White, Blue/Red, Red, Blue/Yellow, Blue/Yellow, Red, Pink, Black.

The "yellow" wire, to which you refer, likely is yellow, with a white tracer (yellow wire, with white mark, at regular intervals).

Hope this helps.

Yours faithfully,

spook

Any idea of the function of the yellow/white marked wire? I disconnected it from the harness and everythnig seems to function...

But a Bigger Question: does anyone have any insight on the Red/Blue 12ga wire? I'm sure that it completes the circuit to the Starter, but this wire is spliced to branch off into 3 separate circuits. What are they and where do they go? If this problem is now just a circuit continuity issue it will make my job a lot easier (saving me unnecessry dismantling) if I know where they terminate.

My Sincerest Thanks!
--
1993 Volvo 940

On my 940, I do not have either the second pink or second black wires. I *think* that I have everything more-or-less wired back the way that it was originally, but not quite. The vehicle is to the point that I again seem to have normal electrical function, with the exception of the ignition. I have determined ground (black) and two hot wires (both red) coming into the harness. All the other cirtuits must be activated by the key switch.

If the flattened portion of the circle spook mentions in his helpful post above runs NorthWest/SouthEast on the harness, then the Ground (black wire) pole is NorthWest(the one to the left of the pair.) My order, clockwise and beginning from this point is: black (ground), open, pink, yellow/white tracer, blue/red, red, blue/yellow, blue/yellow, red, open.

Could either of the red or blue/yellow wires be switch dependent, causing a short? I've examined the "autoelectric.ru" circuit diagrams and Alldata.com, but these aren't providing me with the level of detail that I need to get back on track with confidence.
--
1993 Volvo 940

Spook,

You're a gentleman and a scholar! That's exactly what I needed to know. I can't wait to get to my garage and put your notes into practice.

--
1993 Volvo 940