When any of you do major electrical work like adding all these aftermarket lights, where do you generally mount your relays for them?

Also, how does one figure how many amp relay you should use?

Finally, did most of you pick up your wiring knowledge from others as I am attempting to do and just go at it the best that you can?

 

Relays, relays? Just kidding. Mounting is very application dependent, as well as the manner in which you wire, but generally, I put relays near the power source (under the hood, next to the main alternator wiring) to avoid long runs of power wire.

Virtually all auto relays that you buy (4 or 5 pin) are set at 30 amps, not much to compute. But if you are adding say... 4 spotlights at 55 watts each, then you are adding a total of 220 watts. Divide by 12 volts to get amps which is 18.22 amps so you would want a 20 amp fuse in the circuit.

Electrical knowledge comes from futzing around and from asking others... best you can ever hope for is to run into someone who has done a bunch of it... second best is this board... seems like no matter what it is, someone has done it.

 

Some simple rules for DC power.

Ohm's law
V=IR

V= voltage
I= current (amps)
R= Resistance

A "Watt" is a "Volt X Amp". Like beastrider said, Amps=(watt/volt).

Been a while since I've looked at my EE books...

 

BeastRider,

Well, you probably being familiar with the way Ford runs the wiring now days on their trucks brings me another question to mind.

You probably know that the positive coming off of the alternator runs to some device(looks like a rubber coated spur with three screws on it) and off of that device connects to the battery and other items. Then the main fuse box is over in the corner on the drivers side.

Knowing this, where would you probably locate your relays in this engine compartment? On the firewall where the positive comes off of the alternator or near the main fuse and relay box?

Thanks for bearing with me.

 

I've got pictures of where I mounted my relays in my explorer here:
http://bart.is-s.com/~explorers/madams/PIAA/piaas.html

 

Thefoyboy,

If you haven't already - check out this site http://lighting.mbz.org/.

Bob

 

Swamp,

Thanks for the reply and yes I have been to that site. It is very useful on how to wire which, thanks to that site, I know understand. The questions that site didn't answer for me, though, were the very ones I asked. Like where to mount the relays and where to draw the power to that Matt has graciously given me an idea on how to do now with his photos.

My questions are typically about location and mounting style and connection. I can figure out the basic schematics, but its always the finding of the right wires to tie into, where to locate new wires and relays, and how to do most of this without having a major meltdown of my trucks electrical wiring.

 

TheFoyBoy -- Mount your relays as close to the lights as possible.

Run 10 gauge wire the longer distance ... and 12 gauge wire the shorter distance. (10 ga. is much larger than 12 ga. - 18 ga. is your original, light duty, OEM wiring harness.)

I used two heavy duty 9007 Sockets, pre-wired with 12 ga. wire, to handle the amperage necessry to run 100/85 watt headlight bulbs.

When finished, the OEM 18 gauge wiring, to your headlights, will only be used to "trigger" the relays. The relays will then transmit all of the amperage directly to your lights. (Instead of routing all that amperage through your light-duty Light-Switch and Bright/Dim switch.)

Run two heavy (10 gauge) wires from, and back to, the power source. (From the Positive post on your battery to your relays, and back to the Negative post on your battery.) If you want to do it Daniel Stern's way, you can come off of the Alternator for the positive leg ... and back to the battery Neg. to ground your relays. The main thing to understand is that the reason for 10 gauge wire is because this will be the longest run in the relay system. The shortest run (from the relays to the lights) can use smaller 12 ga. wire.) Bigger wire and shorter runs are better when it comes to losses in amperage.

Ideally, the distance from the relays to the lights is just a few inches. The closer to the light, the better. In the case of headlights; A short distance to one light and a little longer distance to the other light. Or, you could mount the relays near the center in front of the radiator. (One for the brights and one for the dims.)

To "trigger" your relays, take both sets of the DIM headlight wires and re-route them to the relays. The dim wires go to the relay that will actuate your DIM lights. One bright wire goes to the relay that will actuate your BRIGHT lights.) The reason to use both DIM wires is because your DIMS are on two seperate fused circuits. If one fuse blows, the other one will still actuate your dims relay. There is only one fuse for your brights, so it doesn't matter which bright light wire you use.

Now, the only load your OEM wiring harness will have is a few "millivolts" to turn your new relays on and off.

To answer to your question: Mount your relays as close to your lights as is practical. Find a good mounting place in front of the radiator.

Hope this has been helpful.

 

My preference is to use the big screw block on the firewall which then goes to the battery etc. Reason: it is a convenient place and easy to reach to tap into 12 volt power with an inline fuse assembly and it keeps from cluttering up the front end of the engine compartment. It is also near the firewall, and thus, relatively easy to fasten relays, wires, etc.

I don't like the alternator hookup because I'm not much on running more loose wires around the engine. I'm not much on the fuse box side because it is already cluttered with the wiring harness. I suppose if you know how to take the fuse block/box apart to connect to exactly what you need, this might be a good place, but I don't have that skill.

Having said that, my power connects have been for stuff that I mounted on my bed cover... lights and electric locks. I think the key is to plan where to run the heavy duty wires for whatever it is you are doing and to try to minimize their length... with 10 gauge you really don't have to be too **** about this, though. YMMV.

 

Beast and Bill,


Thanks for the replies. They definitely have given me something to cogitate on.

I think my only real concern here is when I have to mess with existing wiring in the vehicle. Two ways where this would come about. One is wiring underbody lighting and then tying it into the dome lighting so that it only comes on when the domes are triggered. The second is rewiring the headlight harnesses for more power carrying capacity.

Both of these would be a major challenge to me because they require messing with the exisiting electrical system and and understand where and how to do that. This is unlike putting in new driving or fog lights where the wiring for these would be completely separate and independent and not require me to mess with either fusebox under the hood or the dash.

I do understand the wire gauge aspect as I did all the electrical wiring in my basement and ran 12 gauge for pretty much everything except for the 240 volt stuff that required 6 gauge.

Like I said, I think my concerns all boil down to doing projects that mess with existing truck wiring rather than all new installations that don't require you to mess with it. On the headlights I could follow the wire back to the fuse box and all, but I don't believe I'd know what to do beyond that and I consider myself to have an awful lot of common sense. As for the underbody lighting, I could wire the power to them with the relay, but I don't believe I'd know how to tire in the relay with the dome lighting to make them come on at the appropriate time.

So many questions and I feel so stupid, but what can you say when you haven't done it before.....oh well, thanks for bearing with me.

 

You're going about it the right way... by using relays and not drawing the current off the existing wiring in the truck, the few tenths of an amp it takes to run the relays is peanuts, and can easily be handled by the stock wiring.

Now, as for where to mount the relays, I put mine here...

http://communities.msn.com/GIJoeCam/...oto&PhotoID=34

http://communities.msn.com/GIJoeCam/...oto&PhotoID=33

I used the 30 amp relays fed from a Blue Sea Systems fuse block (it's a marine fuse block available at West Marine or Boat US, or just about any marine store). I drew the power off the battery side of the accessory relay right on the firewall. (This also makes a great switched power source if you need one) I couldn't find anyplace that had 5 of the same relay on the shelf, so I went with the ones I could find. For the KCs, I used the same length of wire to each light, and just looped the excess out of the way (so one light isn't brighter than the other).

For the switches, I used a small DPDT center off switch (from radio shack... don't have the part number offhand) and a dual color LED (also from Radio Shack) to indicate which power source is used.

Here's the end result:

http://communities.msn.com/GIJoeCam/...to&PhotoID=100

I can explain the switches and LEDs in more detail if you'd like...

Hope this helps...

-Joe-

 

Joe,

Continue please.....I am enjoying the knowledge I am gaining. The one thing I seem to be gathering is that when you do aftermarket lighting add ons that it is best to use a fuse block as well where you can join multiple lights off of it. Do I gather that correctly? And each individual light on that fuse block can be individually controllable, correct?


I know that there has to be a fuse between the battery and the relay, correct? How do you determine how much that fuse needs to be? Do you connect a relay for each light or each set of lights? I guess that would depend on whether or not you want each light individually controllable, correct?

Isn't the rewiring of the headlamps more complicated than this because you have to mess with the engine bay fuse box? If so, this is where my concern comes in.

If I wish to run underbody lighting, don't I basically run a 10 or 12 ga.wire to a fuse or fuse block and then to a relay(1 in this case since I want all 4 to 6 underbody lights controlled as one) for each individually controllable light I want and then maybe a wire from the relay to the dome light switch to turn it off and on or maybe a special switch if I also want to be able to control them off of a switch?

Appreciate your teaching and patience with me.

 

To "hide" my relays, I removed the large black cover over my radiator, which is held down by about 12 screws. After you have installed your relays, replace the cover and .... Viola! You have a very sanitary, hidden installation. (My truck is still under warranty and I didn't want to send up red flags for the service guys to stumble over if other electrical problems should occur.)

To build an auxiliary lighting system on your truck .. here is a partial list of local suppliers, and most of the component parts and basic wire you'll need:

You can buy basic wire, in different colors, and all the basic wiring connectors at both ACE Hardware and Radio Shack stores:

10 gauge - Buy 8 feet (ACE Hardware) in Red to run from the power souce to all of the relays in the group.
10 gauge - Buy 8 feet in Black to ground all of the relays
back to the ground side of the power souce (battery).

12 gauge - Buy 10 feet in Yellow to run from the relays to Brights
12 gauge - Buy 10 feet in Blue to run from the relays to Dims
12 gauge - Buy 10 feet in Black to run from lights back to a connection block where your 10 gauge wire goes back to battery.

18 gauge Wire (To run from your existing lights to the relays (clip your BRIGHTS (Lt. Green/Black) wire and use new wire to run back to your Brights Relay.)

Clip the DIM (Dark Blue/White) wire on BOTH lights and use both new wires to run back to the DIM relay. Both lights because each DIM light is on a separate fuse in your OEM wiring harness. If one fuse should blow, you'll still have power from the other DIM light, to trigger your relay and still have headlights.)


You'll find all of these component parts at Radio Shack. They also have basic wire on the reel:

30 Amp. Relays - Four Spade
30 Amp. In-Line Fuse Holder
30 Amp. Fuse (Box of 3)
10/12 gauge Butt-End Electrical Connectors (Pkg. of 8)
18/22 gauge Butt-End Electrical Connectors (Pkg. of 12)
10/12 gauge Ring Connectors (Pkg. of 6) Use 2 to securely fasten wires to the battery post connectors.

Female Spade Connectors (to attach wire to relay spades) (Pkg)
A. 10/12 gauge (Pkg. of 8) to connect from batter and to lights
B. 18/22 gauge (Pkg. of 12) to connect OEM "trigger" wiring Wire Fasteners and screws (to hold wiring where you want it. Shrink Wrap Tubing (to cover open wiring connections neatly)

 

Bill,

Thank you for that response. It is most helpful again. Between printing everything from you and Beast, I am developing quite a file on this stuff and hopefully will get over my trepidness about doing electrical work.

I appreciate all this and any more you can continue to offer will be greatly appreciated and filed for use.