[67cruiser]

I have,nt got any background on relays put lately seams ive read where more and more guys are installing em on the electrical systems, without completely confusing me??? Does a relay just reduce currant flow??? Explanation of its purpose would be helpfull, should you use one somewhere in the electric fuel pump area>>???

[BILTIT]

Basically a relay is used so that a low current source is used as a switching circuit(on/off) for a high current circuit (low current switching of high current contacts). That was alittle confusing, here is a very common example with older vehicles: normally the headlights on an older vehicle are dimmer than they should be, this is due to the battery voltage having to go from battery to dash and through the light switch itself then to the lights and back to ground through old and small wires and connections. A relay is installed so that the voltage that goes through the switch now turns the relay on/off, the relay in turn is wired so that it takes battery voltage to the lights and back to ground with all new wiring and connections (and alot less of these connections). Since the relay is usually mounted near the lights themselves the amount of cable used is from the battery to the relay and then to the lights and to ground (much less than stock wiring). I usually use larger wire than the stock harness used in the vehicle to ensure adequate voltage/current. It is actually alot simpler than all this sounds but i could not get it out of my head any better than this at the time. I hope this helps.

Yes, a relay is used with an electric fuel pump so that the pump gets full battery voltage without fluctuations (other draws on the circuit). The relay is turned on/off by the ignition switch and/or oil pressure switch, the relay then delivers full batt. voltage to the pump.

[johnsma22]

A relay is basically a switch. It uses magnetism created in a coil of wire by electrical current to open and close a set or sets of contacts, making and breaking curcuits as needed. For example, in a home A/C system a relay in the condensing unit outside is "pulled in" by 24 volts when your thermostat calls for cooling and in turn closes a set of contacts connected to "line" voltage of 220 volts and turns on the compressor. In this case it allows a high voltage motor to be started with a low voltage switch. There are too many different applications of relays to list here but you get the idea.

In the fuel system of a car a relay allows you to start the fuel pump by turning on the key. The fuel pump would draw too many amps to have it directly wired into the ingintion, but the ignition can be used to "pull in" a relay that would close a set of contacts that are wired directly to the battery to start the fuel pump. Hope this helps.

Check out this link. Very basic but good info http://electronics.howstuffworks.com/relay.htmon relays

[johnsma22]

Sorry biltit,
you answered as I was typing. I guess I'm a little slow on the draw.

[BILTIT]

No prob! Different ways of explaining are always a good thing, everybody 'gets' things differently. Nice one on the ''howstuffworks''! I love that site, very informative.

[vidguy]

Good Thread. I always wondered about that as well.

[rgto273]

A little advice, when you find relays, don't take them out unless you are replacing them. I thought I could bypass my heater relay, and ended up burning half my fuses at once when my hot wiring blew.

[Robert Williams]

http://www.madelectrical.com/electri...adlights.shtml