headlamp high beam

[betty]

Hi
Time for the MOTon my98 rreg cse lpt.Checked lights and found nearside high beam out.Replaced bulb though tested OK .Fuse OK-took 2 large relays out of my 97 cse and exchanged but no light still.Earth continuity is OK.Could somebody explain how they would use a tester to find the fault?You have realised that I am not too good on electrics!
Thanks,John

[Mark B]

You need to check whether you are getting 12V to the bulb. I had a similar problem last year with the side light. Some thing had gone strange, probably due to corrosion somewhere, and although I could measure >11V at the bulb socket just feeding a meter, the bulb wouldn't light due to the resistance in the wiring. The sidelights (and probably the headlights) are fed via the big NATO spec connector half way down the nearside of the radiator. I ended up running a new lead from there to the light. I'd check for a wire of an appropriate colour at the big connector and go from there.

[betty]

Thanks Mark
It proved to be the Hella lamp control relay in the end-Saab 41 09 070 or hella 5KG005675-01.After the hella name there is PA6.I am now more confident with the meter!Don't know if Eurocarparts or GSF sell the relays-anybody recommend car electrics in Glasgow?Car has done 120000 by the way.
John

[djtaylor]

Thanks Mark
It proved to be the Hella lamp control relay in the end-Saab 41 09 070 or hella 5KG005675-01.After the hella name there is PA6.I am now more confident with the meter!Don't know if Eurocarparts or GSF sell the relays-anybody recommend car electrics in Glasgow?Car has done 120000 by the way.
John[/b]

Don't buy one, it's usually the solder joints that have cracked. Pop it open and re-solder along the bottom of the PCB to where it joins with the pins.

David.

[Mark B]

Very interesting Betty. I was wondering whether you were getting a warning light with the mainbeam failure, but it sounds like a failure in the warning system caused the light failure. Car's too clever by half!

[djtaylor]

Very interesting Betty. I was wondering whether you were getting a warning light with the mainbeam failure, but it sounds like a failure in the warning system caused the light failure. Car's too clever by half![/b]

That's exactly what happened with mine except my problem was with the bulb filament monitor.

The wire shunts in the following photo are used to measure the respective drop for each monitored bulb

http://nodomainname.co.uk/Saab/lampcontrol1.jpg

and it's the solder along the bottom of the PCB here that cracks http://nodomainname.co.uk/Saab/lampcontrol2.jpg

First I knew was when I took the car for an MOT (summer use and hadn't been driving at night for weeks) and was told a headlight didn't work. I was pretty surprised because the bulb failure hadn't shown up on the pictogram. Of course, technically, the bulb hadn't gone but it was a failure in the monitoring device that failed to show the failure of the bulb to work.

David.

[betty]

David
I was just building up confidence in electrics but now realise a lot more to learn.Would'nt mind reading a book on 12v electrics and getting some knowledge because I also have a boat where it's even more critical.Any suggested titles?
John

[djtaylor]

David
I was just building up confidence in electrics but now realise a lot more to learn.Would'nt mind reading a book on 12v electrics and getting some knowledge because I also have a boat where it's even more critical.Any suggested titles?
John[/b]

To be honest I don't. What sort of information are you looking for? Reason I ask is that there's really no difference between whether a circuit is running at 1V, 12V or 240V or 400,000V, only how far the spark will jump and how big a fire it can cause.

Car electrics are as you appreciate 12V (except for a few variations) and are negative ground which in practical terms just means that the bodyshell is used as one conductor, the ground, earth or negative connection. Most problems with car electrics are straightforward as they are usually wire, switch, fuse, connection or device (bulb, motor etc.) failures. Tracing the failure is usually a logical process of following the circuit from the source, i.e. the battery, through the fuse, the switch, the device and back again.

The entertainment with car circuitry particularly, is that when something fails, it can find an alternate route to earth and i'm sure you may have witnessed cars with flashing reverse/brake/tail bulbs instead of the indicator for this very reason.

As far as boats, the same principles apply but obviously if the boat is plastic, it can't be used as a return path so you've got extra wiring. That's about where my experience of boat wiring goes so I won't profess to offer any more help there.

Some car electric faults often seem to require the assistance of an exorcist such is the nature of the problem

Describe a bit more about where you feel you're at and where you want to be.

David.

[racingsnake]

Haynes do a good book called 'Autmotive Electrical and electronic systems'

http://www.amazon.co.uk/Automotive-Electri...4508&sr=8-2

just found this as well

http://www.amazon.co.uk/Automotive-Electri...4508&sr=8-1

[djtaylor]

Haynes do a good book called 'Autmotive Electrical and electronic systems'[/b]

Both of those look like they could be pretty good. Good find, more appropriate than anything I had in mind. I have this one http://www.amazon.co.uk/Automotive-Diagnos...8382&sr=1-1

but it is mostly what it says on the cover although it does cover "systems" but is limited as to what you can do on a Trionic car in terms of fault code reading. Can always measure the sensor though to see if they're in spec.

David.

[betty]

Thanks to David and racing snake.I will look in to the suggested books and pick one.Re the light control will open as suggested and see if soldered joint opened.Work p/t in a dental hospital and technicians are used to fine stuff if I can't do it.Now for the hazard light relay!Hope to remove from under dash am and see what has happened.
Confidence building up with all your coments.
John