32 replies to this topic

[Bobkennedy]

Again. 1994 1275 Sprite with some erratic battery light behaviour

When first started and engine running. No battery light lit and measuring 12.9 across the battery terminals

As soon as I rev or drive the battery light illuminates, but the voltage across the battery rises to 14.5v.

It’s almost as if the battery light seems to be funcitioning in reverse.

It seems that the alternator is working ok. (It was replaced a number of years ago however has done less than 500 miles since. Just seems to be an issue with the battery light circuit.

Thanks for reading!

[Bat]

Hi,

Check main feed to alternator and the engine earth.

Then disconnect the alternator and with the ignition on the light should be off.

Next connect the thin brown and yellow wire to earth and the light should come on.

If all of the above is ok  then it's the alternator, it might be the brushes sticking.

Cheers 

[Bobkennedy]

Earth strap looks good

Can’t see any issues with the main feed to the alternator. Is there a way to test this? Surely it’s good if I’m getting charging voltage at the battery?

Disconnected alternator. Engine running. Earthed brown yellow. No light.

Plugged all back in. Same thing again.

Edited by Bobkennedy, 29 June 2018 - 07:40 PM.

[hunterg30]

You should not run the engine with the alternator diconected

[Spider]

 Earthed brown yellow. No light.
 

 

If you've done this with the Key ON (engine running or not doesn't matter), then the wiring to your lamp is 'back to front' in that it has an Earth on the other side of it where it should have a +ve feed via the key.

[Bobkennedy]

Earthed brown yellow. No light.

If you've done this with the Key ON (engine running or not doesn't matter), then the wiring to your lamp is 'back to front' in that it has an Earth on the other side of it where it should have a +ve feed via the key.

How on earth. That might take a bit of time to sort. But at least I know light on is good for the mean time LOL

Engine was running. Earthed the wire in 3 separate locations just to make sure.

[Spider]

How on earth.

 

Good question.

 

I'm now wondering if in fact there's a broken connection to do with your instruments / warning lamps and this normally +ve side is now Earthing via a the instruments and other lamps?

What type of instruments do you have (centre, twin, triples or custom) ?

 

Also, does your Oil Lamp behave normal?  That too has a +ve (normally the same one) on the other side of it.

[Bobkennedy]

Triples in front of the wheel. Recently replaced from a pair (both are acting the same)

Oil light behaves correctly

Thanks!

[weef]

You have to understand how the system works. When the ing is turned on 12v is fed to the lamp and the earth return is through the alternator, so the lamp lights. When started the voltage on the alternator side rises to 12v and as there is not volt drop across the lamp it goes out. Your problem will need to be traced using a multimeter on the small alternator wire monitoring this voltage and observing the lamp . It sounds that the vehicle wiring is correct what your description.

[Homersimpson]

Just to check, you haven't replaced the bulb with an LED one have you?  

 

As described above the system works by applying battery voltage (say 12.9V) to one side of the bulb and then connecting the other side to the alternator.  When not running the bulb earths through the alternator and lights, when you start up the alternator generates power which should also help increase the battery measured voltage (say 14v) and so the voltage on each side of the bulb is roughly equal and so it goes out.

 

LED bulbs need a lot less votlage to light and so may come on if the difference between one side and the other is slighty different due to voltage drop in the system.

 

That said 14.5V does seem quite high on the battery.

 

As mentioned above if you get a multimeter, disconnect the wire to the bulb and measure the voltage across the two point of disconnection this will give you an indication of the voltage difference, alternativly remove the bulb and measure across the connections.

[Bobkennedy]

No led bulbs.

Went out and started this evening and it appears I do not have a functioning oil light bulb. It does not light on ignition then extinguish when running. It’s just doing nothing.

So another twist cause it was definitely working.

I shall try and get out in the coming evenings to measure across the bulbs at the different ignition points to see what the change is.

[Bobkennedy]

Even more confused on this one now as it appears the oil light isnt working either. 

 

The ground seems to be good as all the rest of the clocks and the illumination for the clocks works, unless there is a separate ground for the two warning lights?

I would really like to fix this issue, but aside from that an external volt meter and oil pressure gauge may be called for.

 

Ive checked all the connections and dont see any broken tracks on the back of the clock unit.

 

 

Just to check, you haven't replaced the bulb with an LED one have you?  

 

As described above the system works by applying battery voltage (say 12.9V) to one side of the bulb and then connecting the other side to the alternator.  When not running the bulb earths through the alternator and lights, when you start up the alternator generates power which should also help increase the battery measured voltage (say 14v) and so the voltage on each side of the bulb is roughly equal and so it goes out.

 

LED bulbs need a lot less votlage to light and so may come on if the difference between one side and the other is slighty different due to voltage drop in the system.

 

That said 14.5V does seem quite high on the battery.

 

As mentioned above if you get a multimeter, disconnect the wire to the bulb and measure the voltage across the two point of disconnection this will give you an indication of the voltage difference, alternativly remove the bulb and measure across the connections.

For measuring with a volt meter, Should i be measuring from one side of the bulb to ground, and then the other, both when engine is running and also when not running? In order to measure the voltage for drop (or not as the case may be?) or am i picking that up completely wrong?

[Bat]

Hi,

The warning lights are grounded through the switch in the unit nothing else.

So the oil pressure switch grounds the bulb to make it light.

In non-technical terms the alternator does the same.

There is a diode in the alternator circuit but that won't have any bearing on the oil pressure light.

Cheers 

[Spider]

It sounds like there's a crack (or two) on the Printed Circuit on the back of the Clocks.

 

The Warning Lamps are not grounded but fed with +12V.

 

If there is a crack as suggested, they can be very very hard to see.

[Icey]

Either damage to the PCB or the pinouts are mismatched. Quick check would be to trace out the white/brown wire and see if it’s going to the oil pressure tell tale.

If that looks OK then trace the white wire as it will connect to both the oil and charge tell tales.