Battery light more revs the brighter it gets

Evening All

When I start the engine the battery light goes off and stays off until you rev the engine. The more you rev the engine the brighter the battery warning light gets.
In 3rd gear at 30mph light is on, change to 4th light goes off, until 40-45mph then into 5th the light reappears at about 50-55mph. I'm not to sure for 1st and 2nd as the speedo is pretty inaccurate up to 20mph

The battery is less than 3 month old.
Alternator was reconditioned at the same time
New fan belt fitted today.

Any help would be appreciated.

Check connections, but it sounds like a faulty alt

I've disconnected the plug in the back of the alternator and cleaned the connection's, still no joy.....

Probably new alternator needed then, had same thing on mine couple months ago. If you've got a multimeter, put it across battery you can check if alternator is charging it and then you will definitely know if is the alternator. You should get over 14v reading when you've got the revs up a bit.
Is the light out when you just have the ignition on?

get a multi meter (DC Setting)- check the battery voltage- start it up turn everything on check voltage.
Switch to ac and recheck voltage. AC ripple would be blown diode in rectifier.

Sounds like faulty regulator or diode blown in rectifier if it glows brighter and brighter

The light is on when the key is at the final stage before then engine goes on, once the engine is on the light goes out on tick over.

I will get a multi meter on it tomorrow in the day light and post the findings.

thanks

Hello, I have the exact same problem with my 1969 Series 2a with new rebuild Generator (dynamo). What did you find was the problem?

Knysna said:

Hello, I have the exact same problem with my 1969 Series 2a with new rebuild Generator (dynamo). What did you find was the problem?

Click to expand...

An Alternator and Dynamo whilst they do the same thing (produce electricity) have very little in common (they both have pulleys!). The Op's issue is probably rectifier related where as yours doesn't have one but 'could' be brush related. If its been rebuilt and isn't working properly it may be worth returning it?

The Defender is a gift that keeps on giving, I'm only laughing cos mines phucked again, best of luck

The generator was bench tested and was hoping for alternate possibility. If there are any suggestions out there, thanks in advance.

The symptoms you describe match a knackered rectifier / regulator in the alternator. Have you done any welding recently or connected the battery the wrong way at some stage?

I have a separate voltage regulator and generator set up. No welding but hook up in wrong way always maybe possible. I'm only had the truck for 6 months not sure what happened before. It does seem to work in reverse oddly.

Have you checked that the belt isn't slipping?

Try tightening it further.

On 1960's vintage motors with dynamo, the output from the dynamo was limited by voltage regulator, usually fixed on the bulkhead. A failed voltage regulator can give the symptoms described.
To show how old I am I had the same problem with an MGA in about 1970.

In order I should test fan belt tightness, dynamo brushes/commutator, then the voltage regulator

Have you actually measured the voltage to see what it does (tick over / reving / light on & off etc)?

I'll check the belt again but seemed correct before. I have measured it but I'll do some more testing and see what the results are.