Alternator on 740SL

My 740SL broke down last night with a possible alternator fault. In the morning I had noticed that the ignition, battery and handbrake lights were coming on intermittently. In the evening the car started ok and I drove for about 10 miles before the light starteds to dim etc. The emergency breakdown man (AA - a very nice man)replaced the regulator on the alternator but the alternator would still not charge the battery.
He then started the engine and connected a wire from the terminal on the alternator regulator to the positive terminal on the battery and the alternator kicked in and started charging until the engine was switched off again. However, the battery light and ignition lights on the dash no longer light before or after starting. The AA man said the alternator was OK and I probably had a wiring fault. My last alternator problem on a 765GLE was similar to this and was cured by replacing the alternator (£350 for the part). Before I take a chance and replace the alternator again does anyone have advice or experienced a similar problem.

Thanks.

[Peter Milnes]

It would be useful to know what year your 740 is. I am not familiar with regulators with terminals on them (except for my 25 year old 66GL). I would personally replace the alternator after confirmation that there is no wiring problem. A better idea of this will be available when the year of your car is known.

All the best, Peter

[sheerwater]

Hi,
If the alternator is like mine you may find that you can recon it very cheaply. Mine is a BOSCH and if you look on the back you will see a black button about the size of a 50p piece and held on by 2 screws. This is the regulator / brush holder unit. Undoing the 2 screws it gently pulls out so you can see if the brushes are worn. The regulator/brush units cost about £20 (intermotor I believe) and are readily available. When replacing there are internal contacts which need cleaning. If the alternator is out then the job is dead easy. As Peter says check the wiring first especially the thin wire to the back of the alternator (usually a spade connector) as any break in this can have the same effect as alternator failure. Cheers Nige PS disconnect battery before working on brush gear!!!! unless you are into arc welding!!!

Peter.

Thank you for your reply. My Car is F registered (British) so the year of manufacture was, I beleive 1989.

Kevin B.

Kevin,
It seems as if your alternator is not getting the initial exitation current that it needs to start charging, this is normally supplied by the current to operate the warning light.
To check this look on the back of the alternator and you should have a thick red cable and a thinner one (red with a black stripe on my G reg) the thin one is the wire from the warning light.
Remove this wire and switch the ingnition on,warning light should be off, connect wire to earth, light should now come on. If this is OK the problem lies in the alternator, if not, you have a problem with the warning light circuit.
If your alternator does need to be replaced you can get an exchange unit for less than £100. Try your local auto electrical specialist or www.eurocarparts.com
Hope this helps, Colin.

[Peter Milnes]

That SHOULD eliminate the biodegradeable insulation problem as after '88 model it was changed for a better quality insulation. The year of manufacture is given by the tenth digit of the VIN which is a letter. If this letter is J then you have an '88 model, if however it is a K then the model year of your car is 1989 model. Volvo model years start in the previous September, whereas British registration letters changed (at that time) in August. So it is quite possible for a car to be older than you think though not by much!.

All the best, Peter

PROBLEM SOLVED.

I started to test the wiring as suggested over the weekend. I removed the spade connector on the small red wire from the back of the alternator and found that the wire had broken about 5 inches from the connector, between the alternator and the oil filter. I wonder if at sometime in the past the wire had been pinched badly by someone replacing the oil filter as the wire was virtually touching the edge of the oil filter and there is nothing else there to damage it. I have joined a new piece of wire to the break and the alternator is now charging satisfactorly. Total cost £4.67

Thanks for all the help.

Kevin B.

[sheerwater]

£4.67p for a small piece of wire!!!! Must be a genuine volvo part!!!! Glad you got it going again. These wire breaks are hard to spot at times so you dont see them cos of the insulation. Cheers Nige