ELECTRICAL UPDATES
No need to blow a fuse, says Peter Hatfield, with old bike electrics. Try these modern modifications on your 12V British bike…
No need to blow a fuse, says Peter Hatfield, with old bike electrics. Try these modern modifications on your 12V British bike…
Ifind it strange that otherwise clever people shrink away and start mumbling into their beer when confronted with motorcycle electrics. Or they think that, somehow, old motorcycle electrical systems must necessarily be unreliable. Not so. Yes, electrics on modern machines such as certain BMWS are very complex, and I for one wouldn’t touch such systems. However, the electrical systems on our old clunkers are very straightforward, and it’s a doddle to make them both reliable and efficient.
That said, I’m no electrician, but I was a computer programmer and figuring out problems in an electrical circuit is far easier than debugging a 20,000 line program. I’ve rewired my 1968 Bonneville with a readymade loom, but was irked to have to modify it to incorporate electronic ignition and relays for the headlamp and horn. I’ve also rewired two bikes, a Trident and a Commando, from scratch and converted both to negative earth. As a consequence, I have had no electrical problems with any of those bikes.
If you see a pair of wires twisted together, with a blob of solder for good measure, and all wrapped in insulating tape, then you know you’ve come across the work of the artful botcher; also, you’ll know it’s time to do something about it.
BATTERY
The battery is the heart of your electrical system, unless you have a capacitor-based set-up. There’s little point in scrimping on a battery, given its importance. Maintenancewise, it’s worthwhile checking the voltage occasionally, with a good battery showing 12.8V at rest. If it’s significantly less, then it’s time to replace it. I replaced one of my batteries after seven years’ service, even though it was showing a reasonable voltage, and used it as a convenient 12V testing source thereafter – it failed totally six months later.
Back in the day, lead / acid was the technology, but I wouldn’t use it today. I have the acid stains on a silencer to tell me that I don’t need this problem. Also, such batteries need to be topped up with distilled water occasionally. No, my battery of choice is based on absorbed glass mat (AGM) technology, where the acid is replaced by soaked matting, and my preferred brand is Motobatt. The MB9U replaces the original Lucas PUZ5A used on most latter-day British bikes. They’re yellow and ugly, but they have a number of major advantages.
AGM batteries do not lose their charge as rapidly as lead / acid. They don’t leak, and are maintenance-free apart from the occasional charge. Most Motobatt units have four terminals, so orientation is never a problem, and the additional terminals can be used to power accessories or for a battery tender lead.
Despite a lower rate of discharge, I always use a battery tender, my preferred brand being CTEK. I like the waterproof connectors, with my fused battery tender lead doubling up as a power supply for heated gloves. What if you have no electricity in the shed? No problem – just purchase a cheap solarpowered tender suitable for 12V.
SINGLE POINT EARTH
The concept behind using the frame, or other metal object already on the motorcycle, as an earth (‘ground’ for our US cousins) is fairly simple: it uses less cable. However, there are many pitfalls to which many of us can attest, not the least of which is corrosion around those points to earth. Such problems lead to dodgy electrics which are often annoyingly intermittent.
The solution to this problem is just as simple: dump it. Yes, forgot the whole idea of using an earth as such, even though the title of this topic is contrarily called single point earth (SPE) – just roll with it. In my opinion, this is the single most important update you can make to the electrics on your machine. The ethos behind this idea is straightforward: all circuits go from the battery to the component, and back to the battery, apart from the sparking plugs which use the engine block as an earth.
Where’s the best place to start? Find an unused lug near the battery. On Triumphs, an ideal place that I use is the old rectifier mount – it’s right near the battery, and is just the right size for an M6 bolt that will be the attachment point for all the old earth wires. If you’re still using that stone-age piece of technology that is the rectifier, or if there is no suitable lug, fabricate a piece of stainless steel strip with a 6mm hole at each end, and fasten it to the frame at one end, with an M6 bolt at the other. Always use a stainless steel bolt, as it won’t rust – we don’t want to cause problems a few years down the line.
Why M6? you might ask. That was the size of the old standard 0BA ring terminal, which has just been renamed M6 for the modern age; plus ça change… That done, crimp a couple of ring terminals to a piece of 3mm² (~ 13 AWG) thin-wall cable, and connect one end to the battery and the other to the SPE. With the SPE in situ, locate all the old earth connections, remove them, and reattach to the SPE. If need be, extend old cables by crimping on a length of new cable along with a new ring terminal.
The headlamp shell may also need attention. If yours has a decent earth lead, make sure it now goes to the SPE. If not, run a new cable from the headlamp shell to the SPE, as the greased steering head bearings will not make a good electrical connection to earth. Also, you may have many components in there that require an earth, so in the headlamp shell I create a mini SPE, which in turn is connected to the main SPE.
Indicators on later classic British bikes typically have only one lead, and rely on frame earthing to function. I drill a small hole in the indicator housing, wire up an earthing lead with a tiny 1/8” ring terminal, and use a self-tapping screw to secure the ring terminal, finally connecting the wire to the SPE.
As mentioned earlier, the engine does require an earth for the sparking plugs. I like to use a piece of 3mm² thin-wall cable from the head steady to the SPE, the head steady being out of the weather, and less liable to corrosion.
Finally, if you harbour any doubts as to the reasoning behind a SPE, check out the wiring diagram for a modern machine. You will notice that the earth symbol is conspicuous by its absence, or at a minimum by its dearth; nearly all circuits return to the battery via cabling.
RELAYS
What is a relay, and why would I want to use such a device on a classic bike? Essentially, a relay is an electro-mechanical device that allows you to switch a higher current using a lower current circuit. It’s useful, for example, if you want to have a higher power horn but to drive that horn you’d have to otherwise update all the wiring to take the extra current, which could mean breaking into the existing loom. By employing a relay, you can use the existing horn switch to drive the relay and re-wire the horn directly from the battery with thicker cable, running the new cable alongside the existing harness.
With some classic bikes, the wiring was not man enough for the job in the first place. That is, the manufacturer has skimped on cable, using cheaper, thinner cable than that
required, which causes greater resistance. Also, old switches may have the corrosion of ages on them, thereby causing a resistance with subsequent voltage drop. However, such cable and switches can still be used to drive a relay. As a simple experiment, take a multi-meter and measure the voltage at your headlamp bulb and at the battery. You might be surprised at the difference and how low the voltage at the bulb is, with the drop of a single Volt causing a much dimmer headlamp. To resolve this problem, use a couple of relays.
Here’s how we do it for a typical positive earth British motorcycle. First of all we’re going to need the following parts:
Two 4-pole micro relays
5’ or 1.5 metres of 2.5mm² (14 AWG) blue/yellow cable plus some short lengths of scrap
Inline 7.5 amp fuse
Terminals: female Lucar ¼” & 3/16”, ring, double female bullet, male bullets, insulating sleeves
As we’ll be stowing the relays in the relative dryness of the headlamp shell, and we need access to the electrics, the first job is to remove the headlamp from the shell. Next, run the blue/yellow cable from the battery area into the headlamp shell, terminating it with a bullet plugged into the double female bullet. Cut two 4” lengths of blue/ yellow cable, terminating each with a ¼” Lucar connector and a bullet. Don’t forget to insulate any bare terminals with an insulating sleeve before crimping it on. Connect these short lengths to both relays’ 30 terminal and to the double bullet. The idea is that the blue/yellow from the battery will power both relays in a Y-shaped configuration.
Remove the dip beam cable (blue/red) from the headlamp, and connect it to the 85 terminal of the relay with a 3/16” Lucar connector. Connect the 86 terminal to earth (+ve). Connect the 87 terminal with a short length of scrap 2.5mm² cable to the headlamp low beam where the blue/red cable used to be.
With the low beam completed, we can now turn our attention to the high beam using the second relay. Remove the main beam cable (blue/white) from the headlamp, and connect it to the 85 terminal of the second relay with a 3/16” Lucar connector. Connect the 86 terminal to earth. Connect the 87 terminal with a short length of scrap 2.5mm² cable to the headlamp high beam where the blue/white cable used to be. With the relays completed, crimp the battery end of the blue/yellow cable to one end of the inline fuse, terminate the other end with a ring terminal, and finally connect the inline fuse to the negative pole of the battery.
And that’s all there is to it, apart from checking your handiwork. Switch on the ignition and the headlamp, and you should hear a click from a relay. Low beam should be illuminated. Flip to high beam, and both relays will click (one off, one on), and high beam should be illuminated. As a final test, check the voltage at the headlamp. You should have a much higher value than before, as that old tortuous circuit of battery to glass fuse holder, ignition switch, headlamp switch, and dip/main switch has been bypassed.
It’s worth mentioning that the old circuit no longer supplies current to the headlamp, triggering as it does only the relay, and consequently the fuse on that circuit may be downgraded by approximately 5 amps (continuous). If you’re feeling flushed with success, you might also like to trigger the horn via a relay – the same principles apply.
REGULATOR / RECTIFIER
Most of the components in the charging system are now well over forty years old, and have been subject to vibration, corrosion, and just old age. Therefore, a great upgrade is to replace the stone-age selenium rectifier and Zener diode with a modern regulator / rectifier (R/R). There are many available, but the R/R I prefer for late 1960 to 70s bikes is the Sparx unit, as it looks just like the old Zener diode with its large finned heat sink, and is a direct replacement.
Not only does it look the part sitting under the headlamp, but is also located in cooling air. Don’t forget that a R/R dumps excess current by converting it to heat via a shunt, and that heat needs to be dissipated by being in cool air. I have seen folk use a Podtronics unit in the same location as the old rectifier, but there’s little by way of cooling air under the seat.
I’ve fitted a Sparx unit to both my 1968 Triumph Bonneville and ’74 Triumph Trident, and they have both been troublefree, giving a constant 14.4V even at idle. Unfortunately, the Sparx unit is available only for single-phase alternators, but with electrical upgrades I’ve never needed to go to the expense of a three-phase alternator.
A bonus to installing a modern R/R is that it makes conversion to negative earth much simpler. It is possible to do this conversion by replacing the +ve earth Zener diode with a -ve earth counterpart, but why bother replacing old technology with old technology? A side benefit of negative earth is that LED bulbs are far easier to source.
DAYTIME LIGHTS
Until recently, modern motorcycles were required to have headlamps on at all times, but now it’s possible to have a daytime running light (DRL) instead. If you have few milliamps to spare, and wish to be seen, then it’s a simple matter to add a DRL to your classic machine. They can be bought for a few pounds, bolted on to the lower fork yoke, and connected to the pilot light circuit. It’s as easy as that.
An alternative option to having a separate DRL is to fit a headlamp with a LED ‘angel eye’ ring around its perimeter. These are very effective, but are mostly for H4 bulb fitment, so be sure that your charging system can cope with the 55/60w current draw of an H4 bulb.
LEDS
Although very untraditional and totally non-original, LEDS still have a place on classic motorcycles. Their allure is longevity, brightness, and lower current draw. I have fitted LEDS into instrument cases, stop / tail lights, and indicators with much success. That said, there are drawbacks. LEDS that are available through automotive outlets are nearly always for negative earth – a problem with the positive earth of some of our classics. However, Paul Goff does sell positive earth LEDS to remedy that problem.
LED indicator bulbs require either resistors, if retaining the original flasher relay, or a flasher relay specifically designed for LED bulbs. I use a relay with a potentiometer to alter the flashing rate. Finally, some tail lights (eg. Lucas L917) have a vertical bulb for which an equivalent LED is unsuitable. Again, there is a solution: a LED light board. These are available commercially, or can be made very simply, as I have done using a piece of Perspex, one large LED panel and one small – there should be a picture somewhere.
The reason I made one is that vibration caused the glass bulb to part company with the cap on my Norton’s stop / tail light, leaving me with no illumination one night. Not desirable.
LED headlamps seem to be a bone of contention. I have tried LED ‘bulbs’ with little success, although Paul Goff does sell LEDS for British pre-focus headlamps that are supposed to be excellent. I have no personal experience with them, so perhaps the readers can contribute via the letters pages.
What I do have experience with is a sealed beam LED headlamp. For many this is a step too far, but it works for me and I have one on my 1974 Trident. The unit itself draws only 20 watts, or about one third that of an H4 bulb. It has a flat beam without a kick-up to the left for our left-side traffic, but I like it, and it’s far kinder on the electrical system with its single-phase alternator. Another benefit is that it comes with an integrated and very bright DRL.
One final use for LEDS is idiot lights. These are more for show than go, and those with symbols appeal to my aesthetic. On the Trident I have replaced the red, yellow and
blue idiot lights with LEDS that have an oil can in red for oil pressure warning, left / right arrows in green for indicators, and a headlamp in blue for main beam. Funky.
FUSES
Now we come to my pet peeve: a glass fuse in a plastic tube with a spring for contact. To have the whole electrical system at the mercy of this set-up is nonsensical in my opinion, and I have suffered its failure. I prefer the now standard ATO blade fuse, or its baby brother the ATM fuse. When replacing the tube with a spring,
I use a fuse box with single input bus with a LED on each fuse to indicate that it has blown – far easier for problem determination. When rewiring, I prefer a 6-or 10-way fuse box, so that each circuit has its own fuse. One word of caution: when replacing a glass fuse with a blade item, downgrade the blade fuse by half of the glass fuse’s rating: eg. replace a 30 amp glass fuse with a 15 amp blade. My understanding is that glass fuses are rated at the amperage at which they would blow, whereas blade fuses are rated at their continuous amperage.
THE END BIT
I hope you’ve found these ideas to be of some interest. They may not be for everybody and certainly would not work for someone who owns a 100 point concours d’élégance machine, but they work for me. Personally, when it comes to electrics I prefer my machines to be 100% reliable rather than 100% original.
I haven’t mentioned 6V systems, as
I have no experience of them. I’ve also omitted electronic ignition and three-phase alternators, as I feel that they are separate topics in themselves. You may not agree with my suggestions for upgrading your electrical system, or you may have better ideas yourself – let us know.
Finally, don’t forget to maintain your electrics when servicing is due.
Make sure that all connectors are secure and corrosion-free. For exposed connectors dielectric grease will prevent the ingress of water and keep corrosion at bay, although I find that a little ACF 50 will do a good job. Don’t be afraid of having a go at electrics. If you’re having problems then just think methodically like Sherlock Ohms – and know that it’s all elementary, my dear Watson…