Gregory Bender

Wiring diagram - relays

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

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Buy a complete relay solution to protect your starter button and headlight switch

Relays are very beneficial anytime you don't want to run a large amount of current through a switch that isn't designed to handle it. Here's how to wire a relay.

Every relay has terminals that are marked. Usually, there are either 4 or 5 terminals, with the following markings:

I think it is most useful to think of the relay as a light-duty switch that operates a heavy-duty switch. Here's how it works. When you activate a hand-operated switch (headlight switch, driving light switch, starter button, etc.), you are completing the circuit between terminals 85 and 86 in the relay. This is the light-duty switch and only requires only a very small amount of amperage to be activated. Therefore, it is very gentle on the hand-operated switch and causes very little arcing across the contacts. Now, once the circuit is complete between terminals 85 and 86, the relay operates a heavy-duty switch between terminals 30 and 87. This heavy-duty switch is able to handle a lot of amperage without the destroying the contacts (typically 20, 30, or more amps for the automotive industry). Using a relay, you are able to operate a device that draws a lot of current with a hand-operated switch designed only for low current devices.

Many modern motorcycles come equipped with relays for numerous devices, such as starters and lights. However, if you are adding additional driving lights to a modern bike, or upgrading the lights on an older bike with higher wattage bulbs, you'll want to install relays to protect your expensive hand-operated switch gear.

Dan Prunuske sells 25 amp micro relays and has a lot of good information on his website.

Here is a list of various part numbers that may help you track down a generic relay: