by Euan McGlynn

No need to be scared of wiring any longer!! Now you have no excuse to have a wiring loom that's falling apart and a Guzzi that leaves you stranded - many thanks to Euan who has supplied this detailed and easy to follow feature on rewiring your Guzzi

This is a short article on renewing the wiring harness of your Guzzi at a fraction of the dealer cost. If you have basic DIY skills this is not beyond anyone. We will start with tools, a decent soldering gun or iron, stripping tool, side cutters, good quality solder and a multimeter are all you will need. We all know Guzzi harnesses are not the best of quality, cable available from specialist companies is both of better quality and thinner wall structure.

You can also improve on what was original equipment, this will improve your charging circuit and we all know it's pretty poor especially if you do a lot of town driving. This article will give you cable sizes and suggest improvements to ancillary equipment supplied by Bosch and CEV. However we will start with the only items you will need a Guzzi dealer to supply. As yet I have not found an alternative supplier for these parts, the main plastic plugs that locate in your headlamp (Fig1). ( click on the thumbnails for a bigger picture)


The plugs and pins both male and female are available from your dealership. All the Bosch and CEV plugs are available from any good automotive electrical suppliers. Some of you will want to stay original with your switchgear but if you want to use your bike on a regular basis I would suggest changing this, as it is easy to plug in and out there is no reason you cannot have both. If you are showing your bike you will want originality, this is coming from a V7 sport owner who recently went back to original switches for this very reason, they are crap! With the sport and 750S as they do not plug in and out too easily so this is not an option. Incidentally any Sport owners reading this I can supply original start switches, but have limited quantities. Let's get on with the technical bit.

To begin with you need to go to your local print shop and have your wiring diagram blown up, this makes things far easier to follow, you can use your old harness as a template or measure it on a bare bike, when doing this the most important measurement will be the outer PVC sleeving remember to leave length for turning your bars!

Now to cable type - there are a couple of choices here, you will find cable comes in standard and thinwall insulation, thinwall is far better for its overall weight and bulk. Apart from the insulation you will also find that it comes in different diameters for different amps carried this is for different applications, charging circuit, ignition circuit, lighting, general wiring.


16/0.20mm 11amps -

32/0.20mm 16.5 amps -

28/0.03mm 25amps -

44/0.30 33amps -

- side and taillights, horns,
general wiring

- side, tail, horns, general wiring

.- charging, ignition, battery feed

- charging, battery feed


To improve your charging circuit I suggest you use 28/0.030 - these are the cables coming out of your alternator (the three yellow wires). This should also be used for your ignition circuit and starter, improves power to starter.

For your headlight use 32/0.20 and for the rest of your wiring you can use 16/0.20. You can use 28/0.30 for all of your wiring as the larger diameter of cable assists the flow of power. I have also listed 44/0.30 this can be used in place of 28/0.30. You will need 2m of each colour, obviously you will need more of some colours that have multiple uses i.e.: Yellow.

You will also require PVC sleeving of different diameters, 12mm or 14mm for your main harness, 8mm for ancillary harnesses, 6mm and 4.5mm. The large sizes you will need 2m of the smaller 3m.

I also suggest you buy some heatshrink to terminate the ends of your harness, you will need this in several diameters. That is the wiring dealt with at the end of this article you can find a list of cable colours you will need. Remember this will have cost you a fraction of dealer prices Ŗ90.00 for a main harness, as opposed to about Ŗ30.00 which includes all the ancillary harnesses as well as the main. The next purchase will be connectors, these are the spade type female fitted to all Guzzis at the fuse box end (Fig2).

Fig. 2

I would advise against crimp type spades even with a good crimping tool these are unreliable in regular use. I would recommend solder type brass female blades 6.3mm, these come to suit two cable diameters 1-2.5mm and 2.5-6mm you will need both, you will also need blade insulators these are the plastic covers for the spade. If you go for latch type spades you can use them in your Bosch connectors this allows them to lock in. Also required are flag spades and insulators for your alternator connections (Fig3).

Fig. 3

For the regulator/ rectifier if you are using standard equipment you can buy new blank plugs from any good automotive electrical dealer. Ring terminals, for earthing and battery connection, bullet connectors for oil pressure switch, braking circuit and indicators. There are lots of good miniature multi connectors on the market have a look at your dealers, good for back lights etc.

Now to assembly - remember with wiring cleanliness is everything and water is your enemy, this is why insulation is important, good earth contacts, as most wiring problems are due to earth faults, always check the continuity with a meter, when you rewire do it all and don't scrimp, don't leave those old cables on your coils, or those old HT leads, or oxidised battery cables. These will all have an effect on performance.

When soldering make sure you silver all wires and connectors before assembly this aids contact and will save you time, don't rush and always measure twice before cutting any cable, when making your main harness take all your cables going up the sleeve and insert them into the pre-cut PVC.
It is easiest to terminate the 15-way connector first and your fuse end will just be tails with no connectors (at this stage don't forget to fit rubber boot to cover 15 way plug) once you have measured where these cables go you can cut and terminate them.

It is best to fit the individual pins first this makes soldering easier, when you have fitted these you can then mate them to the plug they do lock in so make sure they are in the right holes, your wiring diagram has a key to this. You will have to make some holes half way up your PVC sleeve for the ignition switch, coils, oil pressure, horns, don't cut this as it will tear later, burn a hole with your soldering iron it seals the edges and stops tearing. It is easier to fit the fifteen cables up the sleeve then the four for your ignition, one for horn and one for oil pressure. Don't forget take your time - lay out the harness and think about what you are doing, it is easier to label each cable colour, what it does and where it goes.

The design of the original harness does have some serious drawbacks i.e.: everything plugging into your headlight which gets the most water when travelling at speed (for those of you that go out in the rain!) not much can be done here without serious redesign, Vaseline or silicon grease are the greatest help here. Some of the ancillaries are none too clever, coils mounted in side panels, this makes for extra long HT leads, and the coils can be easily moved to under your tank (Fig4).

Fig. 4

Fig. 4a

The regulator/rectifier, I would advise changing this for a solid state combined unit, there are several choices here, Bosch make their own fitted to later BMWs, Newtronic (which I prefer) (Fig5), and Silent Hektik

Fig. 5

Not only does this save space but also these units are far more reliable the only drawback being some of them will not run the charge light. Other areas worth looking at are electronic ignition (Fig6, 6a) unit can be mounted in old coil location, several manufactures make this, again more reliable, but if it does go wrong you're stranded!!

Fig. 6

Fig. 6a

ELECTRICAL COMPONENTS - High output coils - manufacturers such as Dyna Hall or Silent Hektek, you will also find most modern bikes are fitted with them, just match up the Ohms and voltage and you're in business. Don't forget Silicon HT leads will make a difference to both standard and high output coils. A lot of owners complain of lack of output from their alternator, there is not much than can be done here without major work, you can fit the newer Saprisa unit employed by modern Guzzis or full digital charging by Silent Hektek, but increasing cable size as suggested will help, the problem is that at low revs the power output is just not there. Starter motor can be replaced for the later Valeo unit, which has a higher horsepower output than the Bosch, it is also lighter, but if your bike and electrics are set up right it should start second press. Switchgear as any Guzzi owner knows can be a bit of an Achilles heel, there are lots of alternatives both old and modern, Seventies Yamaha combined lights/horn/indictors are very good and alloy in construction the only draw back being no light flasher (Fig7), just look around and see what takes your fancy.

Fig. 7

I have recently discovered a good start/stop switch alternative, made by Domino (Fig8) it goes well with a Tomasselli throttle (Tomasselli are part of Domino), you will find it fitted to the Aprilia RSV1000. Equally Honda do a separate start/stop of good quality fitted to most of their R series - Ebay can be a good source.

Fig. 8


Most manufacturers do combined throttle/start/stop so if you fancy changing your switchgear donšt forget to take this into account when planning your layout. I hope this brief article will be of some help, if you have basic mechanical skills you can achieve this easily and improve your wiring and general electrics. As with any mechanical task check your work over test all your connections with a multimeter, check all your earths and make sure they do go to earth, most of the wiring problems I have seen with Guzzis are due to corrosion. If you have to buy tools look for a soldering iron with a fine tip this will make your joins neater, multimeters can be bought quite cheaply, shop around.

WIRING COLOURS: Yellow, red, black, brown, green, grey, blue, pink, white, orange, purple, green/black, blue/black, red/black, white/black.

The photos hopefully will encourage you to make some improvements; with a Guzzi any weight saved is a blessing so good luck. I can only supply the name of one supplier for bulk electrical goods in the UK but they are very good and I would highly recommend them;

Vehicle Wiring Products (Catalogue available). 9 Buxton Court, Manners Industrial Estate, Ilkeston, Derbyshire, DE7 8EF U.K.
Tel: 0115 930545 Fax: 01159440101


MY GUZZIS - As for the other parts you should know where to get them i.e. any good Guzzi dealer. I hope the wiring diagram is of help. I have owned Moto Guzzišs since 1978 when I bought my V7 sport when it was six years old, it was imported into Scotland from America by a mate of mine hešs regretted it ever since. In 1979 I bought my four year old burned out S3, this bike had been in a local dealers and sat in his showroom for two years before it was sold. I used to admire this bike but it was far more expensive than the Triumph's on sale and I never had the money, that's why I jumped at the chance to buy my V7 sport in '78. Little did I realise that the S3 would come into my hands, the owner had an unfortunate dropping of the bike and subsequent fire, and I still have a melted Dellorto. I have since restored both, the V7 sport in 1980 and the S3 in 1983. At the moment of writing the S3 is undergoing further work and I am also building an 1100 hybrid Tonti framed sport. The '72 V7 sport continues to evolve the last addition being an optional Guzzi screen, sourced by Teo Lammers in Nimegen Netherlands, he's a bit of a Sport fan with more sports than I have ever seen in the one place, his shop is well worth a visit. http://www.tlm.nl