64 replies to this topic

[GraemeC]

Earthing the brown/yellow at the alt should not extinguish the lamp.

The lamp goes out when the alternator is charging and putting over 12V onto this wire.

[Wiggy]

As above really. The lamp is fed by 12V from behind the instrument cluster. The other wire then goes to the alternator. Before you start the car you have 12V at one side of the lamp and 0V at the other. (The alternator isn't doing anything). When the car is started and the alternator is charging, you have 12V at both sides of the lamp. There is 0 potential difference (another way of stating Voltage), so the lamp goes out.

[Tonylamb]

The big one or the small one?

[GraemeC]

Brown/yellow - there should only be one

[Tonylamb]

I was talking about crazy about Mini's comment that I should check the plain brown wire on he positive side of the solenoid for 12v.

[KTS]

Excuse the pun, but I think we're getting our wires crossed here

Cal844 response was I think to fault find a possible cause of the ignition lamp staying on (i.e no output from alternator), but if the brown/yellow wire from the alternator is not connected to the ignition lamp as it should be, then for reasons wiggy and Graeme gave above, it's not going to get you any further to solving the problem

[Tonylamb]

Pun excused LOL. I agree Im just trying to find a simple way of testing what is going on. I've done so much wiring its possible I've cocked something up. Firstly I've changed the dials behind the steering wheel for a central pod vintage style. That meant a re wire with a small loom. Then the ignition switch didn't work as a starter switch. So I replaced that with a starter button. I also used the old starter solenoid, as shown previously in this thread as a relay to go with the new starter so something there may be wrong.

To recap the red light comes on but DOES NOT go off when the engine is running. The battery isn't charging because I tested it with a multimeter at the battery. With the engine running the battery is showing 12.6v. If it was charging it would show 13 plus I'm thinking. So either I don't have something connected somewhere or its connected wrong. I understand that the circuit that runs through the dash with the red light is very important because without that wired correctly the alternator will not charge.

where should I start as far as tracing the wires back from the alternator to find the point at which problem may be occuring.

[smurfomatic]

Silly question, but are you sure the alternator actually works properly? No good chasing a wiring problem if that isn't where the fault lies.

[Tonylamb]

its a brand new alternator so i suspect the issue is in my wiring

[KTS]

As far as I'm aware the brown/yellow wire is not involved in controlling alternator output - the one that does that is (..or should be..) the brown/blue wire which should connect to the same point as the main alternator output wire (thick brown)

Have a good look at the thin brown wire you referred to earlier (post #28) and see if it does in fact have a thin blue stripe

One other thing to note is that the ignition lamp wiring is unusual (compared to all the dash lamps) as it has no earth - if you've managed to install it with an earth connection it will be permanently illuminated whilst the ignition is on. The standard ignition lamp holder caters for this, so unless you've changed/modified it, it's unlikely to be the issue.

Edited by KTS, 06 January 2019 - 02:25 PM.

[Tonylamb]

The thin brown wire does have a blue stripe. this wire is connected to the old solenoid per the pictures I posted earlier in this post. in fact the earlier post shows how the car is wired asfar as the ignition is concerned. I'm starting to think that the problem is in the newly wired dashboard.

From what I understand brown and yellow wire goes to the red ignition light. once the charge is equalised across that wire it would go out because it has 12v both sides? but if it is wired wrong the alternator would not be triggerred into charging the battery. I'm going to look back at the pics I posted of the wiring of the dashboard. I think the yellow and brown wire should go to the red light and then from the light to the voltage regulator.

This is very frustrating because I just can't work out what is wrong and car is pretty much ready for the MOT otherwise.

[GraemeC]

From what I understand brown and yellow wire goes to the red ignition light. once the charge is equalised across that wire it would go out because it has 12v both sides? but if it is wired wrong the alternator would not be triggerred into charging the battery. I'm going to look back at the pics I posted of the wiring of the dashboard. I think the yellow and brown wire should go to the red light and then from the light to the voltage regulator.

You’re correct about the operation of the lamp, but it should be connected to the yellow/brown on one side and an ignition live on the other. This could be taken from the B terminal on the voltage regulator, but not the ‘output’ side that connects to the gauges.

[Tonylamb]

looking back at the pics I took of the dash wiring the brown and yellow wire is connected to the red light and the white wire from the bulb to the B terminal on the voltage regulator. I think that is correct. Would it be better to use an alternative ignition live for this connection. If so where would it be best to take it from? I think all the white wires are connected together for the dash power. This is frustrating because i'm sure its something simple but I cant find the problem.

[Tonylamb]

I'm now a little confused.  The main wiring I have is per the attached diagram.  It all seems to work except the battery clearly isnt charging.  12.5 volts at the battery with engine running.  

 

Which wire controls the charging of the alt?  The brown and blue one at the main terminal?  Or the brown and yellow one at the indicator light?  Before I take all the dash apart will the Alt only charge if there is 12v both sides of the alt charging light??? Or is that just an indicator and the alt charges regardless if the brown and blue is connected.  Apologies if I've misunderstood but I appear to have conflicting comments.  It would seem to make sense that unless the charge light is operating correctly the alt wont charge.  If that's the case can I run a separate live to the other side of the charging light to compmete the necessary circuit.  I wonder if my temp gauge will also be affected if the wiring in the stabiliser is off or missing something.  Cheers.

Attached Files

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[Tonylamb]

I found this in another post on the forum.

 

It's true. With MOST Lucas alternators you have to have a functioning warning light or the alternator will not charge.

I'd like to make a few minor corrections to Phaeton's explanation. When you turn the ignition switch to the "run" position, current from the switch flows through the warning light to the field coils in the alternator. The "other side" of the field coils are connected to earth. When you turn switch, you are providing power to energize the alternator field coils. The warning light turns "on" because it has a path to earth through the field coils. Once the engine starts, the alternator starts producing electricity and the internal electronics "self energize" the field coils by providing voltage to the internal connection point where the charge warning light wire connects. When that happens (when the alternator brings the internal connection of the small spade lug up to charging system voltage) both sides of the warning light are "high" and there is no path to ground for the warning light... so it goes out.

If the warning lamp is missing or burned out, the field coils will not energize and therefore, the alternator never starts making electricity. OK... that said, there are many alternators that have some residual magnetism in the steel parts the field coils are on. SOME of those alternators will have enough magnetism that a really strong rev of the engine (like sudden burst of 4k RPM or more) can "kick in" the electronics and the alternator will start charging. This is the exception, not the rule, and you shouldn't count on it working every time. Another thing to keep in mind is that you cannot use an LED light (by itself) for the charge warning light. The LED will NOT let enough current flow through it. An LED will light up without allowing the field coils to energize.

You measured 12.5V with the engine running. Take the same measurement with the engine off. You should see about a 1.5V increase in the potential across the battery when the alternator is working. Most charged batteries will measure about 12.5V at rest so you should be looking for 14V or more across the battery for a working alternator to be charging.

 

​So that answers the question as to if you have to have the charging light working.  I think I need to take the dash out and see if either the bulb for the ignition light is earthed which it shouldn't be and if the wire coming from the voltage regulator is actually live with 12v which I understand it should be?  If my wiring as shown in previous post is all fine.  I think it probably is it would seem to be down to the wiring of the ignition light.  I wouldn't be surprised if the issue was there because I changed a lot of wires over from the original gauges.  Can someone point out any glaring errors in this statement or in the wiring diagram above.

 

​Thanks all.