Triumph Club – Vintage Triumph Register » Page not found

Lucas Electrics?

Sorry, we couldn't find this page :(

Electrical Instructions for Replacing the Generator with a GM Alternator in a TR4

by Dan Masters,

Important Note: this entire article assumes a previous conversion to negative ground!

Method One (Utilizing existing wiring)

You are finished!

There are two things, however, to be aware of:

  1. Triumph did funny things when they built these cars, so your car might not match the configuration above, and it may well have been modified by a previous owner.
  2. You now have an alternator capable of more than twice the output of your old generator, but the wiring capacity has not changed. If you add heavy loads, driving lights, high power stereo, etc, you can exceed the capacity of the wires. Also, If you let the battery discharge completely, the alternator can possibly recharge with enough current to overload the wires. If your battery is completely discharged, recharge it with a charger rather than push starting the car and letting the alternator recharge it. If you must do this, keep a close watch on the ammeter, checking for overcharging. Under all other usages, the wiring should not present a problem. The main advantage of the higher output is the ability to provide a higher charge rate at low RPM and idle. The standard loads on the TR4 do not require a higher charge current at normal engine speeds, so the alternator will not be called on to provide enough current to overload the wires.

Method Two (Upgraded wiring)

If you wish to upgrade the wiring to take advantage of the higher output, it is really quite simple.

As above, except:

Cut off both ends of the large Brown/Yellow wire - at the old generator and at the control box - as close to the wire harness wrapping as possible (or, unwrap the harness, and remove the wire all-together). Connect the Brown/Blue and the Brown /White wires together at the control box.

Instead of connecting the large Brown/Yellow wire to the new alternator, add a new wire of at least 10 Ga (8 Ga preferred). Connect one end to the screw terminal at the alternator, and the other end to the terminal on the starter solenoid where the main cable from the battery and the two Brown wires are now connected. Leave the existing wires at the solenoid connected. Very carefully route this new wire alongside the existing wiring harness, and use cable ties liberally for support.

Now, the alternator can provide full charging current without worrying about burning up the wiring.

There is one downside to this approach: The charge indicating light will work as before, but the ammeter will only read discharge. It will register the current being drawn by the various loads on the car, but will not indicate if the alternator is charging.

If you wish to add extra loads, such as a high power sound system, connect them directly to the battery, properly fused, of course. Loads connected directly to the battery will not be indicated on the ammeter.


There are several other ways to do the replacement. For example, you may wish to use a larger range ammeter, or you may wish to replace the ammeter with a voltmeter. If so, contact me with your preferences, and I will try to provide the appropriate instructions.

You may also choose to use a different alternator , rather than the GM unit. If so, it will be wired very similarly to the above, only the connections at the alternator itself will be different.


Entire contents copyright 1995-2005 Vintage Triumph Register. It is unlawful to reproduce, transmit, either in analog or digital form, any content contained herein. With some restrictions, VTR chapters and zones may utilize this site's content. Click here for details.

Questions or comments about this site? Please email