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Hello folks, still coming to the end of a very lengthy TR4 rebuild and having a problem with the charging system. I have a new loom, a new battery,  a new dynamo and a new control box but the ignition light stays on when running. I tried the old control box in case the new one was poor quality but same result. Have downloaded test information for the control box but electrics isn’t my strong point and I’m really struggling. Any thoughts please? Am in Milton Keynes just in case there’s an auto electric wizard in the area!!! Cheers, Phill

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If the wiring is correct - I would first suggest polarising the dynamo - have you done that?



Peter W

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If you have a multimeter there are some simple tests you can do.

Disconnect the brown/yellow and brown/green cables from the D and F terminals of the control box.The brown/yellow cable should have continuity to the large output connector on the dynamo. The brown/green should have continuity to the small field connector. Both should have a very low resistance to earth showing that the windings in the dynamo are OK.

Connect the wires together and connect a voltmeter from there to earth. Measure the voltage with the engine running at about 2000 - 2500revs.  There should be 14 volts or more. Don't over-rev the engine because the voltage will rise with revs and if it gets too high it might just damage some insulation. (unlikely but possible).  

If the voltage is very low there is a problem with the dynamo itself. Try flashing the field again by briefly connecting just the brown/green to 12v - a second or so is enough - then repeat the test. 

If that doesn't work there must be something wrong inside the dynamo - perhaps the brushes are not making a good contact. 

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