1996 960 Electrical Challenges

[Volvosaurus]

Hello Folks,

My driver's side heated rear seat and hand brake light failed some time ago.

More recently, the light has come back on from time to time, totally without movement of the handbrake.

Most recently, the seat base has warmed up (briefly) , but without action of the switch.

Finally, the alternator, replaced last summer, has lost it's charging output. This was evident by a selection of dashboard lights staying on dimly. I replaced the ignition key switch unit, but this has made no difference.

I have checked the wiring in the centre console area, and there is no obvious damage.

I am at a loss to work out how these events may be connected, apart from some wiring loom catastrophe.

The alternator can be replaced, but I don't want to do this if there risk of damage to the regulator thorough stray voltage/current, especially from the heated seat circuits.

Can anyone suggest what might be causing these symptoms? Any help much appreciated!

[Forrest]

I suspect your issues with the heated seat are separate from the problem with the dash lights.

Dash problems are common on old Volvos and could be at the root of your issues with charging and the handbrake lamp. The alternator needs the no-charge lamp circuit working to initiate its charging output. When you first turn the key to position 2 the switched 12v goes via the warning light on the dash and grounds through the thin D+ wire on the back of the alternator. Once the alternator starts charging D+ goes to near the same voltage as the battery and hence current no longer wants to flow that route. There are various diodes involved in both the alternator and the dash to make this magic work.

If your dash lights, especially the no-charge and SRS lamps, are staying dimly lit when the car should be running normally it means that there is still voltage flowing from the dash via the D+ circuit OR someone has been in there already and introduced another (high-resistance) route to ground.

A bit of testing would not go amiss. If you temporarily short the wire on D+ to ground and turn the key to position 2 does the no-charge lamp (and other warning lamps) illuminate normally?

The handbrake warning light is a simple circuit via the bulb to ground via a very cheap and simple switch. Have you checked for a good ground at the switch near the handbrake? Is the switch working? Is the wire intermittently shorting to ground elsewhere?

https://www.ebay.co.uk/itm/281539047550

There is a lot that can go wrong with the heated seats. The switches, thermostats and heater pads are all prone to failure. A good initial test is whether you have continuity through the heater pads.

Would strongly recommend a logical approach to testing the relevant circuits. Good luck.

[Volvosaurus]

Forrest,

Thanks so much for taking the time to reply.

I am a self-employed IT/telecomms installation/cabling/faulting engineer, so I'm used to dealing with ancient equipment and strange faults, albeit not with auto electrics! I also ran a Citroen XM for a number of years, which helps build character.... :-) Thankfully, electrical problems were rare.

When the seat and handbrake indicator light issue first arose, I was hoping to find damaged wires in the central console, as I've been in there in recent times to deal with a handbrake issue. Also, the level of weirdness of faults pointed to the ignition switch unit, which I replaced. No change! Drat!

The remanufactured alternator was sourced through the excellent PFS Parts in Wellingborough, and they report that failures of these are quite rare. They come from a long-established trade-only supplier in Bradford with an excellent reputation.

Thanks again - I thought that forum members were metaphorically running in the opposite direction after so many had read the post without replying, so your response is much-appreciated. I will carry out your recommended tests and advise.

Rob.

[Volvosaurus]

I'm not really much farther forward, apart from doing the tests that Forrest recommended.

I have attached some photos of the results.

Photos show the lights with the D+ in normal, earthed, and finally normal with engine running.

I was aware of the handbrake switch connection. What mystified me was that, with the connector off the spade to the switch, it would still come on occasionally, pointing to some other issue, possibly a rogue earth or leak. Now reinstalled, it works fine, which is about the only electrical thing that does. I switched it on and off via the lever just to cheer myself up... :-)

Are there any basic earthing points that I can check?

All help and advice gratefully received. I've been "home-spannering" for over forty years, can usually fix most things (including a Citroen XM!) but this snag fills me with despair. Auto-electric stuff has always been A Dark Art to me, despite my day job in comms./I.T,

I hope that this is not The End for my 960.

The alternator is quite recent. I can't determine from the test results if the fault is with the alternator regulator or something on the car putting it out of action as described by Forrest. (I'm not thinking quite straight due to a virus) I don't want to spend time and money shipping it back to the supplier for them to declare "no fault found".

Rob.

Update - running the engine with a multimeter from the D+ to earth gives a constant reading of 10.34v. In this test configuration, engine running, the dash lights go out! A drop tester caross the batter gives around 12.5v There is no charging current (14,0v - ish, normally). If the alternator is getting what it needs from the rest of the car (a flow from the warning light area), is this now all pointing to the regulator having failed?

Apologies for all the questions! My virus-fatigued brain isn't working that well, and I'm on the extremes of my knowledge and experience!

[Forrest]

Hope you feel better soon.

I don’t think this fault sounds serious enough to spell the end of the car. The challenge is that auto electrics can be complicated to DIY and expensive to buy in expertise.

I wouldn’t expect the alternator to start charging with the D+ wire disconnected. It relies on +12v from the battery via the charge lamp on the cluster through D+ to excite a coil in the alternator to start the charging output. If you suspect this circuit is not working properly you can mimic the effect by attaching a wire to this terminal and touching it to the battery positive long enough to get the alternator to start charging. For extra safety you can include a bulb in circuit to limit the current through this test wire.

For more information on this try Googling Alternator Exciter Circuit. You could also try watching this video which helps get across what I’m trying to explain but makes slightly heavy weather of it.

+ YouTube Video

It would be worth trying a test along the lines above to narrow the fault to the car or the alternator.

If by applying battery voltage to D+ with the engine running you cannot get the alternator to start charging then that is a strong indication that your new alternator is faulty. If it does, then you’re back to trying to troubleshoot the car.

[Offgrid]

I'm currently restoring a couple of 740s, and I've hit a number of electrical problems. Most of them seem to come down to bad earthing, oxidised switches and contacts and a couple of broken wires. Fixing the issues is cheap and easy once you have located the source. I've been using an aerosol switch cleaner, and I often use this even if there is no apparent problem. A small abrasive wheel or flapper on a Dremel is a simple way to clean off rust. Painting or a bit or Vaseline protects the connection after reassembly.

[Rversteeg]

Has the alternator you replaced last summer ever been working properly? Sometimes it takes a while after new brushes have been put in to have sufficient contact area on the rotor before the alternator starts charging.

[Volvosaurus]

Hello,

Thanks for your interest.

Yes, it's been fine, but the electrical problems did start a while after I fitted it (not immediately), so I can't rule out some problem with the regulator. No idea what type of problem, though, apart from something weird, such as an unstable output.

[Forrest]

Firstly, I have found a better video for explaining what goes on in the alternator with the exciter wire, voltage regulator and rotor/stator coils.

+ YouTube Video

The alternator is actually quite simple with components (diodes, coils, etc.) that generally either work or don't. On these Bosch alternators of that vintage the voltage regulator is integral with the brushes and is usually replaced as a unit. The Bosch voltage regulator rated at 14V will output 14.4V when cold and 14.0V when hot. If the alternator has been refurbished the regulator might have been replaced with a non-OEM one with slightly different characteristics.

Given the difficulty accessing the alternator in a 960, I would feel inclined to check the security of the connections (noting with caution that one is live and direct from the battery) and especially the earth the other end of which might have corroded as Offgrid says. I think the alternator grounds to the chassis nearby.

As I said before, I don't think your heated seat issue is related to the potential alternator and dash lamp issue. Also, unless your car has been really messed with in the past the heated seat is unlikely to damage anything else as even if it took a massive surge it should be protected by a fuse which will blow before any damage occurs.

12.5V is not indicative of a flat battery, so unless you have charged it separately it must have been getting charge. If you do the test bypassing the warning lamp but exciting the alternator directly from the battery if it doesn't start giving out a higher voltage than the battery this will be reasonably conclusive of an alternator fault. If you take it out of the car again you could try the bench test in the linked video to be absolutely certain of your ground before returning it under warranty.

I'm suspicious of the alternator only giving out 10.34v on D+ and if it is doing that in normal operation it would explain the dim dash lamps staying on. However, it doesn't sound as though in your test you managed to "excite" the alternator into firing up its AC output via its stator coils so maybe that was just a stray voltage generated on the rotor coil. In normal operation D+ and B+ should be the same voltage, hence no current flowing via the warning lamp.

As an aside, what short of switch do you have on the heated seat and is its tell-tale light working? The heating pads are thermostatically controlled and only work below a certain temperature. Your symptoms are consistent with an iffy switch (again per Offgrid) and conditions not always being cold enough for the heater to come on.

[Volvosaurus]

Thanks so much, Forrest, for taking the time to give such a detailed and informed reply.

Yesterday, I used a spare battery to give 12v to the D+, protected by a bulb as you suggested, with the grounding to the -ve of the car (on-board) battery.

With the engine running, the drop tester still showed around 12.5v, so it looks as if the alternator is not giving charging output,(13-14-ish) even when fed by 12v to the D+.

In this state, the dash lights went out into a normal running state. I still can't work out if this is a good indication or not. With the car in the "normal" state, the dash lights all come on.

I have ordered an exchange alternator. My concern, probably irrational, is that something on the car might damage this regulator, so I'm no farther forward, but the cost of a regulator the poorer!

Once again, thanks for your kind help. Credit needs to go, too, to the excellent Jamie at PFS parts, who has been most cooperative.

Rob