In general terms it's preferable to use relays to keep the current flowing through the switches to a minimum. That's what I plan on doing once I start on my wiring.
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Use relays to power your lights, horn, or any motor like an electric fuel pump or fan. Your lights will be brighter and the motor will spin faster. Powering the ignition directly is fine. The reason to use a relay is you can use a lighter gauge wire from the component switch to the relay, and your component will be powered directly from the battery through the relay. Some components such as a fan thermal switch turns on by grounding the relay. Horns do also. It's safer to turn the component on by grounding because if there is a problem with the toggle switch, the only thing that will happen is that the component turns on. If the hot side were to switch, you might get a short to ground if the switch were to fail. Additionally, any relay that powers a motor should have an internal diode. This will prevent voltage spikes and add to longevity of the component and the relay.

 

switches and relays

What cobraDVM said . . . relays are used to switch high amperage loads like headlights, fans, horns . . . the switches are used to activate the relays and usually carry less then an amp in current. This make the back side of your dash a very low amperage area . . . you don't want to have all the load of the entire car running behind you dash, bad things happen that way.

HTH

Doc

 

Diagrams

Here are some online diagrams that use switches and relays.

Fan and Horn Diagram

Lights Diagram

There are other diagrams there, too. See the tabs at the top.

Hope this helps.

LNJ

 

Here are some online diagrams that use switches and relays.

Fan and Horn Diagram

Lights Diagram

There are other diagrams there, too. See the tabs at the top.

Hope this helps.

LNJ

Larry

In these diagrams, what does B+, S+, F+ represent?

 

wiring diagrams

Good post Larry

Thanks for the links above

 

Great post Larry and timely. Getting ready to start electrical.

 

Do most aftermarket wiring harnesses (RF, Painless, etc) come with the relays or is that something you need to add to them?

 

NICE!
I need this kinda info...dont want my roadster to be an inferno.

 

Larry, What is the B+ that is to the right of the Fan Circuit Breaker in your Fan and Horn diagram?

 

I wondered the same thing at first, but i think it is the Battery Positive Terminal.

 

B+ is battery +, and is a direct connection to the battery or a junction block that has a direct connection. It's a good idea to use a circuit breaker or fuse link on this wire.

 

Thanks. I have the 20a breaker that came from the donor power windows. Can I use that? or should it really be 10a?

 

thanks, just what i need

john

 

On adding the circuit breaker in the fan relay circuit, I am changing mine out to a fuse, and replacing the auto reset breaker that came in my thermo switch fan kit.

There was a post a couple of months back with a fire that may have been caused by one of the self reseting breakers on a fan. On a fan circuit, the breaker can open and close a number of times without notice, and without allowing for the wiring to disipate heat eventually causing a fire.

-Scott

 

Switches should never be used to control high current applications over long distances. Use relays

 

Are relays incorporated into the wire diet that Art does with a factory harness from a 4.6? Or is that something that has to be addressed independently?

 

I guess I should use a relay for heater switch??? what about wiper motor???, seat heaters??

 

Larry

The factory five heater comes with a switch capable of handling the load of the blower fan. The system was designed with the circuit in mind. I put relays in my wiper motor circuit that help with the park function, but a heavy duty switch should be able to supply the load of the wiper motor. The seat heaters I received from a forum vendor have a relay for each heater. Relays are great when needed, but remember that everything you add to the car is increasing your potential for something to break. Relays are very reliable, but don't overdue.


Jeff

 

IS the ffr wiper switch heavy duty, it looks kind of lame, If i use that then I guess should add a relay??? Cool so no relay on heater (saved $8), I'll see if my heaters came with relays, if not may add.

 

Larry, I think Silverstreak meant that the supplied heater switch was heavy duty, and that you could get a heavy duty enough switch for the wiper. I don't think he meant the switch that comes with the wiper is actually considered a heavy duty one. Least that is the way I read his post..

Of all the boats I have owned over the years, there have never been any relays used for the wiper motors, or the bilge blowers, etc., so there are definitely some good switch's available that can easily handle the amps on thir own. Having been a boater for over forty years, I have never heard of a fire in a boat, from a switch overheating.

 

bump

 

Ok so either upgrade switch or add relay??

 

what sort of switches R people using, and from where. I plann on using red covers, so I would like them to fit under there...

 

Here are some high amp toggles that will work with your switch covers.

http://www.delcity.net/store/Heavy!duty-Toggles/p_788974.a_1

 

Heavy duty toggle

This is the toggle I was talking about. http://order.waytekwire.com/productdetail2/M37/44225/TOGGLE SWITCH 3 SCREW/
It handle 50 amps. There are several styles to choose from.

 

Will the included switches in complete kit handle the load???? will they work with red covers????