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Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by tecton, Jun 13, 2003.
id like to know to..i know you can buy them in kits with al lthe wiring cuase im going to be puting some lights on my roll bar and push bar when i get it.
get a switch
get a 30a relay
get some wire
your done, lol
i just want to make sure
Looks good to me.
Don't forget to put a fuse in there.
forgot about that
15amp fuse sits inline from the battery
wait a second, lol
should that be a 30amp fuse?
relay is 30amp...mabye thats why i keep blowin fuses, hahaha
Most people do not switch on the ground side. Most people put the switch on the pos side.
What wattage of lights are you running?
its the hole on the relay for the switch
they are 100w
gonna get 150 white bulbs soon tho
but its 100 now, and if it matters....going to be 150
Uh, yes it matters if you keep blowing fuses. If you're using 2 100 watt bulbs it's drawing 16.7 amps. If you're going to be running 2 150 bulbs it'll be drawing 25 amps. I'd use a 30 amp fuse.
use the proper wiring for 30a anyways. I'd swich on the positive, not the negative, since your truck is negatively ground. And of course, dont forget to give your lights a good ground, if your hooking it up that way. I personally like using a full negative return line.
Here you go:
And make sure all the wiring can handle current equal or greater than the fuse. ie don't use 30amp wire with a 35amp fuse, the wire will burn up before the fuse if there is a short.
NOT trying to hijack here, but what exactly is the point of a relay? if u have a fuse in the line, and a switch... why do u need anything else? other than get a lot of wires attached to it, what *exactly* does a relay do? this has always confused me...
To my understanding, a relay governs the flow (amount) of current....all a fuse does is protect it from to much. Now i'm sure if i'm wrong, i will be set straight /forums/images/graemlins/thumb.gif
A relay is basically a heavy duty switch that is controlled by a small magnetic coil. When activated, the magnetic coil in the relay "flips" the switch on. The coil and the switch are electrically isolated from each other. In this case, the relay is used to keep the high current wiring for the lights outside of the cab. Also, the coil side of the relay only needs about 0.1 amps to turn the relay on, so you don't need a heavy duty switch in the cab, you can use nearly any switch. There are hundreds more uses for relays, this is just one that is usually done for safety and the convenience of not having to run a large gauge wire through the firewall or wherever.
Basically so you aren't tryin to push the thirty amps through the switch. Relays are designed to handle the jolt. Most automotive electric switches aren't.
oh ok, that makes sense. Someday I'll have to have a trick custom dash like SW does in the green jimmy... lots of switches n stuff. lights are pretty much the last thing on my list tho.. i dont wheel in the dark. lol!
i do, and i freak about lights...ive gone through like 4 pair before i foudn these
if i need to land a plane, or spot aliens or strippers in the dark...im coverd
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but what exactly is the point of a relay?
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A relay allows a small current to control a large current. The small current is all that's required to energize the coil inside the relay. The coil is wrapped around an iron core, which becomes an electromagnet when voltage is applied to the coil. This magnetic field then pulls the contacts for the high-current portion of the relay into the closed position (and actually opens the normally-closed side of the relay, but that's for another time... /forums/images/graemlins/wink.gif ) which now completes the high current side of the circuit, sending voltage to your lights (in this case).
In electrical wiring, resistance is the enemy. In a 12 volt system, just one or two ohms of resistance can create a noticable voltage drop in the circuit (which means dimmer lights in this instance). If you route power from the battery, across the engine bay, through the firewall, to the switch, then all the way back to the lights, you have a lot of wire between the power source and the lights (and you have to use a really beefy switch to handle the high current). Longer wire = higher resistance. /forums/images/graemlins/frown.gif Not to mention you now have some fat wires stuffed up under the dash. This becomes a real problem if you're running mulitple sets of lights.
The relay is mounted under the hood and now power goes from the battery, to the relay, and then directly to your lights. You have a much shorter current path and less resistance in the path, due to the shorter wire between the battery and the lights. /forums/images/graemlins/cool.gif You can run very small wires to the switch on the dash, as that part of the circuit is VERY low current. (On newer vehicles, where the computer controls things, a single transistor is all that completes the circuit for things like fan relays, fuel pump relays, MAF relays, etc. When the computer commands one of them to turn on, a transistor switches on and completes the circuit to ground for the coil in the particular relay.) /forums/images/graemlins/thumb.gif
Oh yeah, the biggest relay on your truck is the starter solenoid. /forums/images/graemlins/eek.gif GM solenoids use a beefy coil that draws 30-40 amps, since in addition to being a switch, it also has to have a strong enough magnetic field to throw the starter gear out to engage with the ring gear on the flexplate or flywheel. The relatively small amount of current that goes through the actual ignition switch is small compared to the 200+ amps that the starter draws. /forums/images/graemlins/shocked.gif Imagine if they ran the fat battery cable all the way into the cab, then through a huge switch that could handle the current required by the starter, then back to the starter... A relay is a much better solution. /forums/images/graemlins/cool.gif
/forums/images/graemlins/thumb.gif Very Nice!!! Thanks for that, I always knew that I needed them just never knew why !!! /forums/images/graemlins/rotfl.gif
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