Gregory Bender

Electricity usage by component

Moto Guzzi V700, V7 Special, Ambassador, 850 GT, 850 GT California, Eldorado, and 850 California Police models


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Please use this information in combination with Wire size/gauge selection for 12 volt circuits and Ohm's law calculations.

Both the Bosch and Magneti Marelli generators are rated at 300 watts at 2400 RPM. Since this is a 12 volt system, this equates to 25 amperes (300 watts ÷ 12 volts = 25 amperes). Or, since the charging system is usually charging at about 14 volts, the equation becomes: 300 watts ÷ 14 volts = 21.4 amperes. In either case, we're still dealing with about 300 watts of power. Where does all this juice go?

Electrical component Watts used with the stock civilian specification Watts used with the stock police specification Watts used with my Ambassador
4 amps max, usually 2 amps
56 watts max, usually 28 watts
28 28 28
Headlight low beam 40 40 55
Headlight high beam 45 45 60
Tail light 5 5 5
Dash illumination bulb 3 3 3
Headlight indicator bulb 3 3 3
Right rear blue light - 5 -
Left rear blue light - 5 -
Right front red light - 15 -
Left front red light - 15 -
Supplementary light (spot light?) - 15 -
Left driving light - - 55
Right driving light - - 55
Right front running light - - 23
Right rear running light - - 23
Left front running light - - 23
Left rear running light - - 23
Horn, brake light, starter, turn signals, most dash indicator bulbs, etc. I will ignore these components as usage is temporal in nature.
Total running low beam 79 134 296
Total running high beam 84 139 301

These calculations are rough and do not take all factors or electrical components into consideration (such as resistance), so these numbers are probably a little low. They are helpful, though, even given the limitations.

Two things are immediately apparent from these numbers. First, the stock system is set up with plenty of reserve, even with the police lights (although I don't know wattage usage for components such as the radio, etc.). Second, adding high wattage bulbs quickly puts my Ambassador at the limit. When the generator cannot produce enough electricity to keep up with demand, the power will be scavenged from the battery. After a while, the battery's power will be depleted and things start getting very ugly. Initially, the lights will dim. But if the situation persists, there will not even be enough power to operate the coil, and so the ignition will start cutting out.