By Pete Snidal, Britbike Nut ( (C)1999

There is no aspect of the Triumph line of motorcycles as badly maligned as the "Lucas, Prince of Darkness" electrical system. Many people actually think it's bad, not knowing that the real reason we've always fondly insulted Lucas electrics is really to keep the prices down on our favourite mounts.

Guess what! The Lucas electrical system is actually a very well- thought out, quality-built selection of components, designed to be compact, efficient, and adequate for the service for which they were intended.

They were once better. Sparks for almost all British motorcycles were at one time supplied by elegant little high-tension magnetos, build by Lucas, which were incredibly reliable even when rudely mistreated. Low volts were provided by a full-on DC generator, with a floating-points mechanical voltage regulator varying field voltage according to sensed output requirements. It was an elegant system, but subject to vibration problems, (the regulator, mostly) and judging by the quality of the construction, was very expensive to build.

Also to replace. The mechanical voltage regulators had a bad habit of taking the generator with them when they went, and during the days that these bikes were available in the 2 to 300 dollar range used, a fresh generator and regulator often cost more than the motorcycle was worth to replace. There was a lot of riding sans lights in those days! And lots of cheap Britbikes with, unfortunately, no lights.

In 1953, Triumph introduced the Speed Twin with a "new" electrical system involving a crankshaft-mounted alternator, and coil ignition, using points, coil, condenser, and thus requiring no expensive magneto. Best of all, the system had no mechanical floating points regulator, and was much less susceptible to vibration and burning itself up. The extra reliability inherent in this system quickly found acceptance by the average Britbike enthusiast. This evolved, if so few changes can so be called, to the system we enjoy today. If you are having trouble with your electrical system, it will usually be found to be fairly easily and cheaply fixable.

What all this tells you is that, if you just can't get the juice you need, you can make some changes, to components newer, stronger, or both. But in most cases, troubles with insufficient output can be fixed a little more easily than this.


"If it ain't broke, don't fix it." Whoever said this was one of the wisest yet most neglected men of out time. As obvious as it seems, there are many owners of Triumphs, like everything else, who can't keep their fingers out of the works, whether or not it's required. So let's be sure you're having troubles before you fix anything. If you're not, then treat this little piece as interesting reading only. We'll look at the two major components of your electrical system: the charging system and the ignition system.

1) The Charging System

The charging system is there to keep your battery up. Since your battery is the primary source of power to everything on your bike that uses it, the charging system must be able to keep up with the demand. But keep in mind, this is on the long-term basis. Short-term demand on the battery can be greater than the alternator can supply, the remainder being supplied by the battery itself. This is why the Brits called the battery the "accumulator." It gives us a bit of cushion in cases of high demand on the system. This cushion may, in cases of extremely low system ability, extend to running the lights to get you home at night - but bear in mind that in marginal cases, you will eventually run out of juice when running with full lights. At these times, the stuttering and stammering of the motor will tell you it's time to make up your mind between lights and ignition - ignition generally wins. A Halogen light can be just enough extra to put you in this category, so be prepared to go back to the ol' tungsten if your system is marginal.


You can always tell when this isn't enough - the bike starts to stammer and stutter after a while, often losing one cylinder, at least intermittently. When you shut the lights off, the reduced draw leaves more power for the ignition system, and the bike runs better again - for awhile. In the dark. Welcome to the land of Lucas! But of course, getting into this situation isn't Lucas' fault - it's yours! And it's up to you to fix it.

So, the first fix we'll discuss is what to do in _this_ situation. Obviously, how you got there is by running your battery down - drawing more from it than the alternator can replace - until there wasn't enough left to continue. Sometimes just turning the lights off will get you home. Sometimes, you'll have to get some juice into the battery before continuing. I've been in this situation more than once, and had to bum a boost from a car owner. In extreme cases, just hooking up to the battery of a non-running car, with a piece of speaker wire, will boost enough for ten or 15 minutes of running - sans lights, of course. So you just hook 'er up, and go back and have another beer or two, by which time the bike will start, and you'll have _some_ time to make it home. Best without lights. It's better in these cases to hook up to a vehicle that's been left running - the charging system voltage is higher than that of a still battery - 13.8 Volts instead of around 12 - and your battery will charge considerably better. But 15 minutes or so of just being connected to a properly charged battery will do wonders. I make a point of including 5 or 6 feet of speaker wire in my toolkit for just this purpose. - Be REAL CAREFUL about polarity! Reverse=charging your battery will kill it dead, and probably finish off your charging system at the same time!

If you ever find yourself in this position, however, you know you've got something to fix. Let's look at how.

First, check your charging system voltage. Before starting the bike, check your battery voltage with a voltmeter. Then, start the bike up, and check it again, with the engine running at about 1500 rpm, and the lights off. This is the charging voltage, and it should be higher than the basic battery voltage. 13.8 would be nice, but in the real world, even 12.8 is decent. Any less than that, and you know your battery's never going to get a decent charge. Now, turn the lights on, and check it again. If the voltage drops below 12 here, you know that your battery's going to be in a state of net discharge when you're running with full lights.

Another consideration here is Just how good is your battery? Since we don't use our battery for starting, it can be in pretty bad shape without giving any indication. Check the connections, and the fluid level. Top up with distilled water if necessary, and allow to stand awhile before charging. Put a small trickle charger on it overnight, and then the next day, connect a taillight to it and see how long it takes to run it down. Since the original Brit specs called for keeping parking lights on overnight, you can expect a good battery to keep the light burning for 10 or 12 hours. I wouldn't run it right down, but if on checking after only a couple of hours, you find it's no longer burning, hike off to your local KMart and git you a fresh one - the Tri battery is a fairly common one, and most places that sell MC batteries stock it. Then let's continue with checking the charging system.


If full lights is pulling you down below charging voltage, you might consider installing a lower-draw "running light" for daytime use. I use a standard bullet-shaped clearance light mounted just under my headlight for daytime running. This way, I know that I'm getting a net charge into the battery during daytime running, so when I need that high beam halogen at night, I'm starting with a full bank account.

Another obvious improvement is simply cleaning and tightening all your connections in the charging system. Locate the connectors from the alternator wires as they leave the primary chaincase. Pull these apart and inspect them for shiny. Clean them as lightly as possible, since they're cadmium plated and you don't want to take off the plating if you can help it. Don't forget also to clean the insides of the tubular coupling sleeves - 8 surfaces altogether. Then do the same for the spade connectors to the rectifier. Be sure also to clean the rectifier's mount to ground. In fact, there's nothing wrong with borrowing a page from J.A. Pan & Co. here, and running a second red ground wire between your major components - from the rectifier mounting bolt to the battery positive terminal, instead of relying on the chassis to carry the current. Copper is always a better conductor than steel, anyway.

If charging is a problem for you, you may want to replace your probably-dried-out selenium rectifier with a Radio Shack replacement. Bridge rectifiers being a common element in electronics, RS supplies a 10 and 20 Amp replacement in modern solid-state silicon version for less than a 10 dollar bill. Be sure to mount it so that it can bleed the heat it produces into an aluminum plate which you cleverly build as a mount. The earlier RS bridges had spade connections, but the later ones seem to be straight wires, so you'll have to solder the wires on. The terminals are marked + for the one you'll ground, - for the one you'll connect to the battery -, and the ones marked AC may be connected either way to the output from the alternator. Also, be sure to "heat sink" the heat from the soldering iron by using your third hand to clamp a pair of needle nose pliers to the component side of the soldering site. Once you're done, you'll likely find that this little improvement makes quite a difference.

If your system voltage is still low after all this, you may want to try disconnecting your Zener diode. The purpose of this baby is .... wait for it ....... to _dispose_ of excess voltage, so that your charging system won't overcharge your battery, burn out your lights, etc. Although hilariously funny to those who find themselves without the juice to get home on dark nights, this is actually a truth for some. I've had batteries boil with the Zener disconnected, even with the lights full on, so be sure to check your charging voltage after you've replaced the diode, and find out if you need to disconnect the Zener. Theoretically, it shouldn't draw any current at all below it's "knee voltage" of 13.8 or so. The more savvy may want to put an ammeter in the circuit to the Zener, and see if there's any current draw below this voltage.

There is also a solid-state device on the market called a Typmanium voltage regulator. It's actually a regulator/rectifier replacement, modern electronics, and is an excellent thing to use if the simpler process described above runs into snags, such as if you need a new Zener. Here's the British Cylcle Supply listing:

332-104/A         TympaniumPowerControl uni EA           75.40

(prices are in $Cdn. I hope I'm not pushing BCS down anyone's throat; it's just that I happen to have a copy of their price list in this box, so they get the mention. There are other good places to get parts as well - see our links page at the egroups tri-twins site
Click here to go there


If you still can't get enough volts up to keep your battery charging, it may be time to replace your stator and/or rotor in alternatorland. The magnetism can go in the rotor, and small shorts can cut out some of the windings in the stator. Here's a list of prices once again from BCS:

391-47205         stator,2 wire,RM21,std.12 EA          158.50

391-47204         stator,3 wire,RM19,120 Wa EA          173.50

391-47244         stator,3Phase,180 Watt    EA          162.54

391-47252         stator,3ph,'79&80 Tri ks  EA          172.54

391-47197         stator,5 wire,RM19,for ET EA            0.00

391-47105         stator,RM13 alt,3 wire    EA          135.00

391-465998        stator,RM14               EA            0.00

391-47127         stator,RM15 alt,3 wire    EA          150.63

391-47209         stator,RM20,early Triples EA          147.42

391-47194         stator,sing.phase,180Watt EA          219.40

391-47239         stator,sing.phase,180Watt EA          182.07

There were also some rotor changes over the years:

391-465969        rotor,RM14 alt,3.250"od   EA            0.00

391-466125        rotor,alternator,2.75"od  EA           90.00

391-60600684      rotor,alternator,late,2.9 EA          194.18

As you can see, this is not a decision to be taken lightly, and you should exhaust the easier possibilities befor going here. As well, however, there is a possibility of upgrading to a more potent alternator than originally supplied. Ask your supplier for interchangability information.

2) The Ignition System

Now, let's look at the other place to fiddle - the ignition system.


Unlike the situation with the selenium rectifier described above, there is nothing particularly old-tech about the coil-and-points ignition system supplied as stock until well up into the '70's. It's a pet peeve of mine that so many people seem to think that the standard system, having in most cases worked completely satisfactorily for many years, all of a sudden has to be replaced with a tacky aftermarket alternative, just because it's solid state. In the case of the Boyer, it's also plastic. It may or may not have electo-automatic advance to replace the centrifugal advance of the standard system, and it has a few disadvantages as well. Such as the designer having taken the shortcut of making it fire both cylinders at once - one because it needs to, the other because, what the hell, it's on the exhaust stroke anyway, so who'd care? (Anybody with a little leak in a pipe who doesn't like pop-pop-bang-bloof noises on deceleration, that's who)!

It seems to me that a major consideration should be the difference in quality. After all, there is a particular old-world quality in the construction of these bikes, particularly in the pre-OIF's, and it really riles me to see people flocking to spend big bucks on replacing that lovely cadmium-plated steel and shiny machined cam, weights, etc. with a not-particularly-brilliantly-crafted piece of fiberglas and epoxy with a few hunks of solid-state sealed within.

The standard Lucas components are very nicely made, are after all the stock ones - we _are_ restorers, aren't we? - and with a mininum of maintenance, will give good service for the life of the motorcycle. Furthermore, there are a number of advantages to keeping the standard points in there where they belong:

  • - You can carry the parts you need to fix it on the road. A spare set of points is about $10.00. You should have them in stock anyway, and they take no room in the toolbox. If a coil lets go, you can get home with a car coil, so you have the necessary redundancy for any trouble on the road. A spare Boyer is, lessee......

    331-02            Boyer ign,TriBSA unitTwin EA          169.00

    so, if I have this right, the price for going to the Boyer ignition, if we're going to have on-the-road redundancy, will be $169.00 X 2, plus taxes........ pushing $400. You can have a new set of pipes for that! Or a new fuel tank almost! Two sets of points are like twenty bucks!

  • - The points are stock. The way she came. Sure, Mikuni Carbs are better, but they're not stock. That's why a lot of us stick with the Anal(s), And I question whether or not that plastic Boyer replacement is even better. Main point (heh heh!): the stock ignition system works just fine. If it doesn't, set it up properly, and it will. The only event I can imagine involving Boyer replacement would be in cases where the auto-advance unit is worn or rusted too badly to use. Lesee, here:

    391-54415746      advance unit,c.wise,5deg. EA          145.00
    391-54416405      advance unit,ccw,10degree EA            0.00
    391-54416150      advance unit,ccw,5 degree EA           85.00
    391-54418404      advance unit,ccw,5 degree EA            0.00

    Oooh! That could hurt! I'm not sure if this is the one for the Tri or not, but it gives us a rough idea. Still, personally, I'd opt for the still-cheaper and still-stock replacement. - And don't forget, you don't need an auto-advance unit! The timing that matters is when it's running, not when it's static. Set your timing for best running (ping timing's my favourite; a light's usually OK) and don't worry about retard for starting - in the days of manual advance Triumphs, even the hot T110's didn't usually need to be retarded to start. If your points are running true and not sloppy, and the cam surfaces aren't pitted, you're in good shape!

    The same applies to converting to Lucas Rita. Made later, made much tackier, not correct anyway. And even more expensive.


    So, what've we got? Basically, if you're having any electrical troubles at all, or even if you're not, a good first step is just to find and clean all the relevant connections. After that, you can begin a step-by-step programme of parts replacement, starting of course with the most easily available. (read cheapest) I won't repeat myself about the benefits of sticking to stock parts if possible (oh - I just did, didn't I?), consistent with functionality being of prime importance. I hope this little treatise will be of help to someone from time to time. And if you came across this piece from somewhere else, you may want to come and join us at the web site mentioned above.

    Keep on Trumpin'!