Wiring Help - Relays

[Alien]

Wiring up some lights in the truck bed (LEDs) and under the rear bumper (aka back up lights).
The LED bed light kit came with a prewired switch that attaches to the bedside and straight forward instructions: Connect one pair of labeled wires to the other sides lights, connect other pair of labeled wires to power/ground.

I want to use the one switch to turn on the LEDS and the rear lights. Don't know what the switch is capable of, nor wanted to wire everything inline, so threw in a dual 87 relay and wired them us as shown. The LED kit had some heat shrink sheething that hides a bit of the wiring, but fairly certain it isn't a big mystery. Power to switch, switch to strip A, strip A to strip B, back to A, back to switch, switch to ground.

Note: Not trying to use the rear lights as back up lights, just as rear facing lights.

I may have the 85 and 86 hooked up opposite than shown.
http://www.fototime.com/F1932AD060FC227/standard.jpg

LED's come on with the switch, rear lights do not. Changed out the relay, same result. The relay isn't switching.

What am I doing wrong?

*edit* I know normally the switch is before the relay, but it should still work after the relay. The LEDs are the variable, but I figured they draw so little current, it shouldn't make much of a difference. Or is that exactly my problem, that the LEDs don't pull ENOUGH current to close the switch?

[Supercharged111]

I hate the numbers even though they're standardized. I had to google to give you a decent answer here. You should have an 87 and an 87A. 87A gets power when the relay coil is not energized and 87 received power when the relay coil is energized. I can see now though that you have 86 plumbed to the LEDs which is why they work. They're getting their power after the relay coil gets its power, this is wrong. 86 should lead to a toggle switch, then to ground. All your switched power should be drawn from 87 and I'm pretty sure you have no interest in using 87a at all.

[Alien]

There are dual 87 relays out there, typically used for aftermarket lights (like KC Daylighters). Both terminals get power when switched, there is no 87a on these.

The LEDS by themselves do not warrant going thru a relay. Here's the LED kit. See how nice and prewired it is.
http://www.fototime.com/E81367141E55C09/standard.jpg

That said, I know I could completely rewire the LEDs and switch as stated. Was really hoping to keep the kit intact.

Just read it's not amps that switches a relay, it's volts. If my theory that the LEDs alone are not drawing enough power, I'm now thinking I may just need to add a resistor to the circuit, between the 86 and sheeting or the sheeting and ground. However, I know LEDs require a certain resistor themselves to work in a 12V system, soooo, while that might get the back lights to work, it may disable the LEDs.... and now my head hurts.

[Pranav]

I really have no idea what's going on with that diagram.

My tonneau LED and back up light wiring setup is pretty simple.

I run a constant hot wire from a dedicated fuse box all the way to the LED strip. LED ground is tied to a grounding switch just inside of my taillight. I can leave it on for days and not worry about draining the battery with all 0.3A of consumption.

For the backup light, I have a 3 position (on-off-on) backlight (when on) SPDT switch on my dash. One side of the switch is tapped into my running light on circuit, the other side into my reverse light circuit (both locations under dash). The switch then powers a wired going to the dedicated fuse/relay box under the hood, which then runs the hot wire all the way to the bumper light. I leave my rear light switch in the backup position so that it turns on when I back up, makes seeing EVERYTHING with the backup camera easy. If I'm hooking the trailer up at night I flip it up the other way so I can walk out back and see what I'm doing.

I recommend getting a small fuse/relay box and putting it under the hood. I run my under hood light, tonneau light, bed cigarette plug, and air compressor off of it, which then has its own 6GA cable going straight to the battery.

[Alien]

Yeah, so you have two independent circuits, one for bed lights, one for rear lights.

I had the rear lights wired pretty much the same way as yours on my Ranger. On on demand, on with reverse lights, or off (if tailgate was on/up). Switch triggered a relay mounted behind a taillight. (I hope/assume your rear lights are on a relay. If supply power is going thru the switch, that's a quick way to burn up the switch unless it's rated for the amps.) Power supplied by a fuse block under a kick panel for all my accessories (rear lights, CB, brake controller, 12v auxiliary power outlet in bed)
http://www.fototime.com/0E8D210C35C3C9D/standard.jpg

Decided this time I didn't want a switch in the cab, and willing to lose 'on with reverse'. Just wanted a switch by the bed. One switch to rule them all. Not planning on all the gadgety stuff on this truck to warrant an additional fuse block.

Doing some digging, looks like the voltage to activate the relay is 8V to 9V. Voltage across the LEDs is 3V to 5V. So for a this 12V circuit, the LED's are leaving only 7V-9V to trip the relay, right on the cusp.

[Fbody383]

Remember a relay is just an electrically controlled remote switch. I can't see your pictures at the office. When you supply 12v to the coil side of the relay it closes the switched side.

If you have 12v rated LEDs you're probably fine and don't need a current limiting resistor for them. You'll see the fuses in the attached diagram - one to protect the switch and one to protect the relay. Obviously one switch could control multiple relays (And, one relay can switch a lot of devices up to it's load rating)

[Storm Trooper]

Wiring up some lights in the truck bed (LEDs) and under the rear bumper (aka back up lights).
The LED bed light kit came with a prewired switch that attaches to the bedside and straight forward instructions: Connect one pair of labeled wires to the other sides lights, connect other pair of labeled wires to power/ground.

I want to use the one switch to turn on the LEDS and the rear lights. Don't know what the switch is capable of, nor wanted to wire everything inline, so threw in a dual 87 relay and wired them us as shown. The LED kit had some heat shrink sheething that hides a bit of the wiring, but fairly certain it isn't a big mystery. Power to switch, switch to strip A, strip A to strip B, back to A, back to switch, switch to ground.

Note: Not trying to use the rear lights as back up lights, just as rear facing lights.

I may have the 85 and 86 hooked up opposite than shown.
http://www.fototime.com/F1932AD060FC227/standard.jpg

LED's come on with the switch, rear lights do not. Changed out the relay, same result. The relay isn't switching.

What am I doing wrong?

*edit* I know normally the switch is before the relay, but it should still work after the relay. The LEDs are the variable, but I figured they draw so little current, it shouldn't make much of a difference. Or is that exactly my problem, that the LEDs don't pull ENOUGH current to close the switch?

You need a ground on 86

[Supercharged111]

. . . I can see now though that you have 86 plumbed to the LEDs which is why they work. They're getting their power after the relay coil gets its power, this is wrong. 86 should lead to a toggle switch, then to ground. All your switched power should be drawn from 87. . .




You need a ground on 86.

[Storm Trooper]

.

Yea what he said!

[Alien]

You need a ground on 86
Yes and no. The ground IS there. It just goes thru the LED's first.

I've figured out the diagram I have would work if either a) the relay triggered at a lower voltage than 8V-9V or b) the LED's had less than a 3V voltage drop or c) the relay triggered with amps instead of volts.
That's why it's not working, not simply because the 86 doesn't go straight to (switch then) ground.

So yes, it looks like I'll be rewiring it.

[Fbody383]

Yes and no. The ground IS there. It just goes thru the LED's first. But voltage drop across the LEDs. Should not be any "load" in the switch circuit.

[Alien]

Yup tho still not an absolute statement. The load just needs to be less than 2V :)

My first mistake was thinking the relay was triggered by amps. Once that got corrected in my head, messed up by thinking that since the LEDs draw low amps (which I assumed as "load"), so they must have a low voltage drop also, and I could get away with using them as the switch circuit. Once I found the relay needs 8-9 volts to trip (wouldn't have guessed it would be that high) and the LEDs themselves are 3V-5V, then it made sense why it didn't work.

I would have gotten away with it if it wasn't for you meddling kids!

[Supercharged111]

I see what you're saying now about voltage vs amperage because they're wired in series, but the relay coil is not meant to carry any sort of load. You should not be powering anything off of 86.