Triumph TR3 drawing


TRIUMPH Contents page  > converting a TR3 from psitive to negitive earth




Triumph Changing polarity from positive to negative earth


I found converting a stock positive earth Triumph electrical system to negative earth to be surprisingly easy. This conversion allowed me to connect a radio to my electrical system.

Only three items on a stock positive earth TR3 electrical system care what the polarity of the system is, the ammeter, coil and the generator.



First I disconnected my battery cables and checked them carefully for wear. I cleaned the terminals and the cable connectors. Next I turned the battery around so that the cables would reach the proper terminals. Besides checking the battery cables and cleaning their connections at both ends, I also checked the cable between the engine and frame. This cable provides a good ground for the starter motor and the spark plugs.


The steps I took to do the conversion:

  • Disconnected and removed the battery. This was a good time to clean out and repaint the battery tray.
  • Switched the leads on the ammeter. The ammeter has two connecting clips. I Just moved the wires from one side to the other.
  • Switched the low voltage leads on the coil. I disconnected the leads, loosened the clamp on the coil holder, rotated the coil 180 degrees and reconnect the wires. That preserved the lead routing.
  • Disconnected the small wire on the generator. The connection post is labeled F or field.
  • Placed the battery back into the battery tray in the opposite direction as it was sitting. Reattached the hold down.
  • Connected the clean ground connector to the negative terminal of the battery. Note: The terminals are different sizes. You may have to replace the connectors or you may be able to open one up and close the other enough to fit.
  • Disconnect the wire at terminal "F". Take a length of insulated wire and connect one end to the battery's positive terminal. Touch the other end of the wire to the field (F) terminal of the generator a couple of times. This generally produces a spark. Remove the wire from the battery. This operation repolarizes the generator. Note: The "F" may be hard to see on the generator so you can do these steps on the wire at the voltage regulator "F" terminal.
  • Reconnected the wire I previously disconnected from the field (F) of the generator
  • Attached the battery cable leading to the starter solenoid to the positive terminal of the battery.

I was done

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