I'm in the process of doing some rewiring of my led fogs and light bar. I'm also about to add led back ups, and I just finished wiring a lighted USB port. I am using mictuning switches:



I was using a per wired harness with relay from them, but wasn't to happy with really how messy it was, especially since I had two harnesses for the current lights and one more to come for the backups.

Truck is a 2008 F150 XLT 5.4L

1. I ran the USB outlet by using an add-a-fuse to fuse F18 (10A, Electrochromatic mirror, Compass, Reverse Sensing System), running the wire behind the dash and to the outlet. I grounded through the firewall to the inner fender well just in front of the intake location (there is an existing ground there from a fuse block). I assume this is all ok, the fuse I added on is switched power like I wanted, the USB port is rated at 3.1A.

2. I redid my fog light wiring. Cut off all wiring and harnesses. Grounded the two lights directly to the frame. Ran both positive leads through firewall to the switch. Switch is grounded, too. Power comes from another add-a-fuse on fuse F32 (15A, Vapor management system, A/C clutch relay, Mass Airflow Sensor, Variable Cam Timing, etc). I'm running 14awg wire for the lights, and the draw is about 24Watts, so I think I'm in the neighborhood of 2Amps. The fuse here (F32) is switched, also. Does this all seem ok? I did away with the relay when I realized my draw was so low. Is this ok for low amperage LEDs like fogs and backups, about 2-3amps?

That and I'm not entirely sure how I'd run the relay from switched power? I will need to for the light bar (about 25amps). Would I run a positive lead from the battery with a fuse to relay (blade 30), ground blade 85, run a positive lead from blade 87 to the lights, and then blade 86? Would that go to the pin on the switch that would normally connect to the lights? The switch is a 5 pin (for back lighting) so there are 2 ground, 2 to battery (or inline fused source) and 1 pin to lights. So again, blade 86 of the relay to the light pin, and the pin that is for the supply would go to my switched power source? I do intend to clean up further down the road using a switched fuse block, but for now this is what I got. Thanks for any advice and help in clarifying if I've got it or not.

 

I found this gem, would this work for me where blade 86 would go to the pin on the switch that normally goes to lighting, and the 12vdc pin on the switch goes to the switched power? Also, the switches are rated at 20amp, so that's another reason I question the need for a relay on a light drawing 2-3 amps using a 10amp fuse with a 20amp switch. Is this correct?

http://www.offroaders.com/info/tech-...ay-diagram.gif

*EDIT*. I've done quite a bit of searching, and just revisited several sites including a Wrangler forum and Pirate4x4. For every 1 person saying they always run a relay, there are 10 or more that say on such a low draw, coming from a power source with fuse, a switch that is rated to easily handle no more than 75% of the constant amperage rating (I'm at 2-3 amps on a 20 amp switch, 10%), a relay is an unnecessary repetitive addition. Of course my light bar will still get the relay.

 

So something went very wrong last night. I decided to add a relay to the fogs. I used the 5 pin switch, jumped 8 & 7 to ground, 2 & 6 to my switched source (fuse 32, vapor management, etc.) and 3 to relay pin 86. Then relay pin 30 to battery with fuse, pin 85 to ground and pin 87 to lights. As I'm driving it gets dark, I put on my headlights and immediately I see the electrical system gauge start to drop, dash lights dim, rpms start to rev up without shifting, airbag light comes on and I hear a very loud rapid ticking. Then everything dies. I disconnect the fogs, pull the fuse for the relay and unplug the add a fuse and install just the regular fuse. Essentially the lights, switches and relay are completely disconnected. Try to start and get rapid ticking, no turnover, no starter even. I get a jump and the truck starts right up Kama I go to put on the headlights and I start seeing the Gage drop again to a point where everything dies. So I get one more jump, leave the lights off and drive home no problem. To me it sounds like there is a short somewhere comma or could I have fried a relay for the headlights? I can't seem to figure out what went wrong because everything was wired according to the cut sheets and I checked all connections and they were fine. What is confusing is if you do a search on 5 pin led switches, there are about four or five different ways to wire them depending on what you want. I guess my big question is I can ground all the switches together, but can they get the12volt accessory power from the same source and jump all those together or do they need to be individual? I know the number 3 pin on each switch needs to go individually to its own relay.

 

I have no idea where you might be getting a draw from with your "fogs" disconnected.

However, as long as your switches are ONLY controlling relays and no other load, you should be able to use a single source of accessory power that can carry enough amps.

It's VERY IMPORTANT to use a large enough gauge of wire to carry the amps you'll be drawing (google wire gauge/amps chart)

If you can't locate a suitable power source, you could always run a fused lead directly from the battery to power the switches, make sure both are large enough.

 

Are you able to draw a diagram of how you have things wired?

 

I'll draw what I have done later today and upload, Patman. 1972-2003f150, I have no idea either! I'm baffled. The power for the fog switch came from fuse 32, a 15A fuse that handles vapor management, MAF sensor, VCT, etc. it's a switched source, what I wanted. That's supplied by 14g wire. The relays are powered from the battery with 12g wire with 30A inline fuses. The grounds for lights and relays and switches are all 14g wire, and the positive wires are all 14g as well. I cross referenced and found for the approximate amperage of my lights I should be fine (about 8' for each run for lightbar and fogs to relays, 6' for positive source for relays).

Again, everything is completely disconnected, the truck held a charge all day yesterday and started up, ran fine. As soon as I turned on the headlights I got a massive draw and things quickly "went haywire". When I get home today in about 10 hours I'll go out and poke around the fuses and relays and I'll get that sketch up. Thanks guys.

 

This is the gist of it. Done this way the lower light of the switch illuminates when the ignition is turned on. The upper light illuminates when you turn the switch on.

 

I think the way you have it wired the switch illumination is in series with the relay

Unless I'm reading that wrong.

You have a link to the switch you used?

 

 

You have another cheap rocker you can pop in and see if your switch is the problem?

Are you sure the switch actually output power and not output ground?


I reviewed the switch diagram and it's not very clear either. Let me draw something out and see what I can come up with

 

Sorry, that pic was blurry, try this one.

 

Thanks, Patman. I wired it just like the diagram shows, with pin 2 & 6 jumped and fed from switched 12v fuse 32. Pin 3 goes to the relay pin 86. Even if there were a problem, Everything is disconnected and I still have a draw somewhere when I turn on the headlights. I'll be home in about 2 or 3 hours and take a closer look at everything

 

To answer your question about how to wire relay with ign power

30 battery
87 output power to lights
86 ign power
85 switched ground

This is my preferred method, using multiple inputs for a single relay.

For your back up lights use your reverse power as your 86 instead of ign if you'd like

 

It's also possible your alternator took a dump and it's just a coincidence that it happened simultaneously as your install

If you have everything disconnected, and the truck is still draining I'd have the charging system tested

 

Update: got home, and even with a good charge, truck will not start on its own. It ticks and clicks. I jump it, it runs. I shut it off, try to restart, it ticks. I noticed if i turn the driving lights on the ticking stops. From the drivers seat, I first heard an audible rapid ticking from this "speaker" device on the interior firewall above and to the left of the brake pedal. Not sure what this thing is:



I then heard the rapid ticking from here at the tb. I confirmed the ticking was here with a long screwdriver.




I heard more ticking and after lots of head scratching and some cursing, realized the sound was behind the seat back.after more cursing when I couldn't find the release for the seat back right away, I finally got it off, ripped away the sound panel, and low and behold, this guy was ticking:




I checked every fuse and they were good. I tried swapping relays in the fuse panel to see if one was bad and got no change. I checked everything as best I could behind the dash at the steering column, pulled the headlights switches, checked all wires and visibly, nothing is wrong. No bare wires, nothing charred or melted or anything. I am stumped to say the least.