The other evening I was driving home in my Lotus – it was cold, dark and raining, so what’s new The heater was on as were the lights and wipers. However when applying the brakes and/or turning on the indicators the wipers would slow down or stop all together. Obviously the dynamo was not capable of keeping up with the drain on the battery. Nothing for it but to fit an alternator.
Now I know you can get an alternator in a dynamo casing but times are hard so with a spare dynamo from a scrapped car and a fitting kit purchased online it was time for the changeover. I know what you are thinking ‘what about the originality of the car?’ Well that’s easy – I have changed the air filter, plugs a few times, got rid of the points and condenser for electronic ignition etc. So one more change will not hurt anyway health and safety don’t you know.
SO HOW IS IT DONE?
I know many cars in the club are positive earth so they should be changed to negative earth first. If, like me, your car is fibreglass anything not bolted to the chassis will need to be earthed.
Swap the battery terminals around by turning the battery around or fitting new cables.
Reverse the wires on the ignition coil. The ignition parts, starter motor, wiper motor and overdrive solenoid can be left alone.
You might have to reverse the connections on the heater blower depending on type of motor used. If you have an electric fan it may also spin backwards and will have to have its connections reversed.
Reverse the connections on your ammeter if one is fitted. The other gauges can be left alone.
If you have an electronic tachometer fitted you either have to replace it with a negative earth type or have it converted internally.
If you have an electric fuel pump you may have to experiment but many pumps are not sensitive to polarity. Only touch the supply wire off the terminal very briefly (to avoid a short circuit. If it works, okay, if not, reverse the connections especially if it is bolted to a fibreglass shell. If it is bolted to a steel chassis it may need to be replaced with negative-earth type.
Finally, the dynamo. Remove the smaller of the two wires (DF or field connection). Use a stout wire to briefly connect it to the positive side of the battery. Repeat this a couple of times, then reconnect the wire on to the dynamo. Job done, hopefully. Remember to take the usual precautions, not naked flames or smoking etc.