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Electrical wiring mystery
https://ausmini.com/forums/viewtopic.php?f=2&t=101877		 Page 1 of 1
Author:  slabber [ Sat Jun 03, 2023 2:59 pm ]
Post subject:  Electrical wiring mystery
Hi - I have a quirky alternator dash light feature on my 72 Clubman. When turning the key, only the oil light glows. However, if I put my foot on the brake when starting (illuminating the rear brake lights), the alternator light also glows going off on start up, as you would expect.
As the oil pressure light works ok, I think this should discount a problem with the power side of the circuit (as the oil and alt circuits are duel to the fuse box)? Just seems strange that the alternator light almost needs to be "primed" by operating other circuits, to get working.
Everything works fine, just annoying, if somewhat quirky.
Any thoughts before I contemplate pulling too much apart?
Cheers
Author:  timmy201 [ Sat Jun 03, 2023 3:56 pm ]
Post subject:  Re: Electrical wiring mystery
With the ignition on:
12v from ignition switch goes to the bulb, then to the alternator signal terminal IND
If you remove the IND wire from the alternator and ground it (key on and engine off) the bulb should light up

If it doesn’t there might be something wrong somewhere along the line
Author:  Dave Dobeson [ Sat Jun 03, 2023 4:46 pm ]
Post subject:  Re: Electrical wiring mystery
Slabber
Most of my wiring attempts become a mystery but I might be able to give you some things to look for..
The oil light and alt light circuits are dramatically different and are not "duel".
The alternator light is "between" the alternator voltage output and the battery voltage so that if the alternator stops working, the light comes on. The lamp has 2 wires and is NOT earthed to the body.
There is a major mistake if the brake switch turns on the light. In my Mk1 the brake pedal switch is to earth; not sure if the Clubman brake, switches the positive or negative. Try to follow wiring colours.
Good Luck Dave D
Author:  slabber [ Sun Jun 04, 2023 10:44 am ]
Post subject:  Re: Electrical wiring mystery
timmy201 wrote:
With the ignition on:
12v from ignition switch goes to the bulb, then to the alternator signal terminal IND
If you remove the IND wire from the alternator and ground it (key on and engine off) the bulb should light up

If it doesn’t there might be something wrong somewhere along the line



Cheers Timmy201, very useful - I tried this (earthing the IND wire) and yes, the Alt light glows as it should.
Does this point to something not right in the alternator itself, in your opinion)?
Author:  Mick [ Sun Jun 04, 2023 12:07 pm ]
Post subject:  Re: Electrical wiring mystery
Is the brake switch still the hydraulic one mounted to the subframe? Or a microswitch mounted to the brake pedals?
Author:  slabber [ Sun Jun 04, 2023 12:26 pm ]
Post subject:  Re: Electrical wiring mystery
Mick wrote:
Is the brake switch still the hydraulic one mounted to the subframe? Or a microswitch mounted to the brake pedals?


Yes, a hydraulic one mounted to subframe
Author:  Mick [ Sun Jun 04, 2023 3:25 pm ]
Post subject:  Re: Electrical wiring mystery
Take a look at the wiring there. There's a positive from the switched fuse directly to the switch. If there's a single wire on the other side of the switch, follow it up to find if it goes directly to the rear loom. There's something funny going on around that wire on the other side of the brake switch.
Author:  slabber [ Sun Jun 04, 2023 6:40 pm ]
Post subject:  Re: Electrical wiring mystery
Thank you for everyone's input, much appreciated.
Investigating further, it is not only the brake lights that get the alternator light to glow, but also indicators, radio etc, or basically anything off that side of the "keyed" fuse block. Items like the headlights, horn etc (ie items off the "non-keyed" side of the fuse block) have no affect on or off.
And on using the brakes/indicators/radio to get the alternator light to glow, upon turning the key back around past the aux position, the alternator light goes off, but the oil light remains on.
Alternator fault or some sort of short on that "keyed" side of the fuse block?
The Alternator works fine and charges the battery as it should when running.
Author:  Mick [ Sun Jun 04, 2023 8:08 pm ]
Post subject:  Re: Electrical wiring mystery
Yeah it will do that. The indicator is just an indicator, it doesn't supply a field or anything to the alternator.

Is there 12 volts on the keyed fuse as soon as the ignition is switched on? Or only if you press the brakes?
Author:  Dave Dobeson [ Sun Jun 04, 2023 8:40 pm ]
Post subject:  Re: Electrical wiring mystery
Slabber;
When the car is running, there should be 12 -14 volts on BOTH wires to the ignition light; so the light goes out. From your "symptoms", one wire (or the light socket) is earthed. It should connect back to the alternator.
(You haven't fitted a LED instead of a filament bulb, have you?!!!!!!!!!!!!!!!!! This defeats the purpose of the light)
Good Luck. Dave D
Author:  slabber [ Mon Jun 05, 2023 3:40 pm ]
Post subject:  Re: Electrical wiring mystery
Mick wrote:
Yeah it will do that. The indicator is just an indicator, it doesn't supply a field or anything to the alternator.

Is there 12 volts on the keyed fuse as soon as the ignition is switched on? Or only if you press the brakes?



Yes, 12 volts appears as soon as the ignition is switched on. Pressing brake not needed.
Author:  slabber [ Mon Jun 05, 2023 3:46 pm ]
Post subject:  Re: Electrical wiring mystery
Dave Dobeson wrote:
Slabber;
When the car is running, there should be 12 -14 volts on BOTH wires to the ignition light; so the light goes out. From your "symptoms", one wire (or the light socket) is earthed. It should connect back to the alternator.
(You haven't fitted a LED instead of a filament bulb, have you?!!!!!!!!!!!!!!!!! This defeats the purpose of the light)
Good Luck. Dave D


Haha no, no LEDs fitted.
As per Timmy201 above:
" 12v from ignition switch goes to the bulb, then to the alternator signal terminal IND
If you remove the IND wire from the alternator and ground it (key on and engine off) the bulb should light up

If it doesn’t there might be something wrong somewhere along the line"


Very useful - I tried this (earthing the IND wire) and yes, the dash Alt light glows as it should.

So I'm just not sure if this in fact confirms the line between key and alternator is operating correctly? ....
and therefore the electronics inside the Alternator is the actual problem?
Author:  Steam [ Mon Jun 05, 2023 5:49 pm ]
Post subject:  Re: Electrical wiring mystery
Sorry I am a bit late into this.
When you first turn on the ign sw there should be 12v going through the ign/alt lamp and it earths through the alt field winding which is grou ded while thw alt is NOT running, thus lighting the lamp. When the alt is running / charging the voltage regulator is supplying 12v to the ind connection thus the lamp which now has equal 12v on each side goes out.
So you need to test if at first whether the lamp is not lit due to
(a) The lamp does not have 12v from the battery. Or
(b) The lamp has 12v on both sides.
Going on the fact that you say the lamp lights when you ground the 8nd wire from the alternator then (b) is li,ely.
Confirm by testing that the ind terminal at the alternator also has 12v. (it should not but I suspect yours will)
The fact that the light illuminates after a load is put on the battery thus creating a voltge drop leads me to suspect the protection diode in the regulator is leaky and is allowing 12 through to the ind terminal until a voltage drop forces the diode to function thus blocking the 12v as it should and leaving it connected to earth until the charge commences.
A new reg should fix but it is not life threatening as it works correctly in all other respects.
I have one here which causes the ind/ alt light to pulse before starting tne engine but I havn't fixed as it all works otherwise.
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