19 replies to this topic

[floormanager]

Your voltage readings are good. They indicate the alternator is putting out sufficient voltage to charge the battery.  

 

I cannot comment about the flex circuit.

Have to say I've learnt something too!  Thank you dklawson

[Scousemouse]

 

Possible but the clue is that he is only getting 12.7V with the engine running.  The alternator is barely functioning; should be 14V on start-up.

 

 

That is true.  However, if the charge warning lamp has failed, a Lucas alternator will not start charging.  You will always see battery voltage (typically 12.5V or less).  As Ethel said, the lamp is part of the circuit that excites the alternator's stator windings.  If those windings aren't powered when the engine first starts, the alternator will not work.

 

As Ethel said, check first that the bulb is not blown.  This is a very quick test.  To repeat Ethel's advice....

Unplug the alternator. 

Make a jumper wire and insert one stripped end of the wire into the SMALL terminal in the alternator plug.  

Switch the ignition to the run position but do not start the engine.

Connect the other stripped end of the jumper wire to a bare metal earthing spot on the engine.

If the lamp illuminates, the bulb is good and you have a serious issue in the alternator.  

If the lamp does not illuminate, replace the bulb.

 

In my case I've just fitted early 3 clock center binnacle(old mini style) to a 91 Mayfair.When I turned on the ignition I was made up the ignition light on the dash lit up...but it stays on all the time while driving.Could this be because the bulb is an LED so has lower resistance thus it's continuously lit?

If so would swapping the ign bulb back to a standard bulb cure this??

[dklawson]

If you are saying that you replaced the regular incandescent charge warning lamp with an LED... then, yes, you need to put the regular incandescent bulb back in the circuit.

 

Electric current has to flow through the charge warning lamp circuit to start the alternator making electricity.  If you use just an LED, it cannot pass enough current to the alternator so it starts charging.  You will be able to drive the car for several days running on just the battery.  However, in short order the battery will run down and the engine will refuse to start.

[Ethel]

It might be the bulb holders, try swapping them around. Careful tweaking of the little contact springs or conductive tape / paint may help.

[Scousemouse]

Thanks guys,I'll let you know the outcome