Alternator Conversions

from the Expert: Dan Masters

"I will be changing the generator on my TR4A to an alternator. Which alternators have been used successfully and what size was it? What kind of mounting problems did you experience? Are you happy with the change?"


I recommend the GM/Delco unit. I have one on my TR6 (62Amp), and it only required very minor mods to make it fit. Took about an hour or two to install. The GM unit I used was a model #7127 (I have bought 3 of them, from 3 different dealers, and they all had the same model niumber, so I assume that is the GM number rather than the parts store's number). Prices for these three ran around $25 each.

If you use this unit, DO NOT use the instructions on the VTR site, unless you use the upgraded wiring method. As I posted a while back, I made an error in these instructions. I sent corrected versions to Ken Streetor to replace these, but he hasn't had time yet to post them. Below is the corrected instructions.


METHOD ONE (Utilizing existing wiring):


Look for the following wires:

Black: Remove and discard.

Smaller Brown/Yellow:

Brown/Green: Disconnect and tie together, with an insulated connector.

Larger Brown/Yellow:


Brown/Blue (2): Using a large, solder type butt connector, connect all 4 of these wires together, and insulate with heat shrink tubing. Be aware - this connection carries ALL of the current for the car, so it must be a good connection. You do not want a high resistance here. You may have to go to an electrical supply house for this type connector, rather than an auto supply store, to get one large enough to hold all 4 wires. Run two wires into one end of the connector, and the other two into the other end.

Remove the control box and, please, save for a friend who is a purist!


You will find two wires, Brown/Green and Brown/Yellow. Disconnect them from the generator and leave in place. Remove and save the generator.


On the side of the case, you will find two spade lugs recessed into the body. The lugs are identified on the body of the alternator as 1 & 2. You will need a plug (connector) for these. These plugs are readily available at an auto supply store, usually in a package hanging on the pegboard display rack in the electrical section, and usually identified as an alternator extension connector, or something similar. If not, the counter man will know what you are looking for. There will be two short wires already connected to the plug.

On the back of the case, you will find an insulated screw terminal.

Connect the Brown/Green wire to the plug wire going to the # 1 terminal, using a butt connector, or splice, solder, and insulate with heat shrink tubing. The plug is keyed, and will only go in one way. Connect the other lead from the plug (#2) to the screw terminal on the back of the alternator case, along with the larger Brown/Yellow lead from the original harness, using ring terminals.

Both the larger Brown/Yellow wire and the wire from terminal #2 connect to the screw terminal.

Disconnect the ground lead from the battery before proceeding with any electrical work, and, of course, follow all the rules of proper wiring practices. I recomend using solder connections, and covering them with heat shrink tubing, but crimp type connectors will work quite well also. You will need butt connectors for attaching to the plug wires, and a large ring connector for the screw terminal. If you would prefer not to have splices, you can remove the terminals, and the wire, from the plug. Using new terminals of the proper type, connect directly to the existing wires, and insert the terminals into the plug. New terminals can be purchased from British Wiring, (20449 Ithaca, Olympia Fields, IL 60461, 708-481-9050) and The Wire Works (167 Keystone Road, Chester, PA 19013, 800-292-1940), among others.

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 TR4A does 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.


Cut off both ends of the larger 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 two Brown/Blue and the Brown /White wires together at the control box.

Instead of connecting the larger 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 a Brown wire 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.