Need electrical help!

[Luke'sScreenName]

I need help from those of you with more knowledge than me. I can do simple wiring but bare with me as I am sure I will use incorrect terminology. I think there is a simple answer here...

I want to add a second warning light to my tractor (MX4800) that will light up when the parking brake is set. I have already done this once following another TBNers youtube video where I tapped into the circuit that activates the dash "parking brake" light. So that circuit powered the dash light and my additional LED light. The problem is the light he used (and I copied) is not bright enough for a cab-less tractor in the sun. I found a low amp LED strobe I want to replace it with. The problem is I need to alter the circuit.

The momentary switch that is depressed when the parking brake lever is set INTERUPTS the circuit when depressed. So setting the brake interrupts the circuit that was inhibiting the light being on all the time (I guess this is a safety feature?).

The problem is the original light I used was designed for motorcycles to flash when the alarm had been armed. It had THREE wires black (neg/ground), yellow, and red (I assume constant power and a "control?"). Someone can help me with the terminology but it must have and internal relay(?) that completes the circuit to power the light when the control(?) circuit is interrupted.

The light I want to install only has two wires (red and black). So I need something that I can control power to the new light by interrupting another circuit. I'm sure there is a name for this but I don't know it.

It is a 5amp circuit.

Help!

 

[s219]

You probably want a "normally closed" relay that would power open when it gets juice and then closes again when you remove juice.

 

[Luke'sScreenName]

Ok so I think what I need is a 12v SPDT relay and power the circuit off the NC pole? What amp rating should I get?

 

[s219]

I guess you'll need to know how many amps the light pulls, but I suspect it would be pretty low if it's an LED.

Also would be nice to know the current draw of the relay and the gauge of the wire on the tractor for that e-brake circuit, just to make sure the wire is going to be able to handle what the relay pulls. The relay will be powered open all the time except when the brake is on, when it will return to closed.

 

[2bON2b]

Ok so I think what I need is a 12v SPDT relay and power the circuit off the NC pole? What amp rating should I get?

The relay should be rated for load and duty cycle. If it is protected with a five amp fuse then the contacts should be rated for at least 5 amps. If it was a circuit that constantly cycled (on/off/on/off) then add %125 or %150 to the size of the relay rating. For your application of a LED lamp on a 5 amp circuit I would be ok with a 5 amp relay.

 

[Luke'sScreenName]

22ga wire I think and less than 1amp consumption (may actually be 500mA).

Common and negative/ground are the same thing for this application correct?

 

[Luke'sScreenName]

The relay should be rated for load and duty cycle. If it is protected with a five amp fuse then the contacts should be rated for at least 5 amps. If it was a circuit that constantly cycled (on/off/on/off) then add %125 or %150 to the size of the relay rating. For your application of a LED lamp on a 5 amp circuit I would be ok with a 5 amp relay.

If all I can find is a 30amp rated relay is that ok?

 

[2bON2b]

If all I can find is a 30amp rated relay is that ok?

Should be OK. Don't want to get it too big because you don't want the relay coil to overload the device that is switching it on. I guess in this case the parking brake switch.

 

[2bON2b]

22ga wire I think and less than 1amp consumption (may actually be 500mA).

Common and negative/ground are the same thing for this application correct?

Yep should be 0 volt DC. Most DC applications like this, not industrial, will use black for the "common and negative/ground" conductor

 

[Luke'sScreenName]

Ok. I was looking at the power consumpition for these things and it struck me as very small. And the resistance should actually go down with a larger amp rated relay right?

 

[Luke'sScreenName]

Thanks for the help guys! I love this forum.

 

[2bON2b]

Ok. I was looking at the power consumpition for these things and it struck me as very small. And the resistance should actually go down with a larger amp rated relay right?

It may due to conductor size that was used to make the coil. If it was listed with a 500ma current consumption then roll with it. I would.

 

[Luke'sScreenName]

Ok. I'll make a trip to O'Reillys tomorrow and see what they have.

 

[skyhook]

Here's a thought,....I don't think you need a "relay" for such a small current involved.
I don't fully understand what you want to do
Do you already have a "park brake light" now and want to install another one along side of it that is "brighter"? If thats the case, just tap your led into that circuit, red to the light you have now and ground the black wire.
When the park brake is activated, both will light up and both are protected by that 5 amp fuse.

 

[whiterose]

Are you sure you need a relay?
Relays are to switch a heavy ( ish) load controlled by a small current that works its coil. The coil switches the relay. Yes a single pole double throw can be used to work your device if it switches on or off by using the correct terminal. Either a NO - normally open/or off or the other terminal the NC one - normally closed/made/on.
See what the led strobe needs in current draw. Connect to a 12 battery directly- hopefully you'll have a multimeter set to current- start high, 10 amps and go down if needed.
If the current is say 5 amps or less you won't need a relay but may find the switch you want to use will switch off when you need it on. Or the reverse of that.
So you'll need replace that switch with a spdt one if possible. Or you'll need to use a relay to do the same job.

 

[whiterose]

Feed the coil direct from 12 v battery and see what the current it takes- Still likely low- guess 1/4 amp or less.
30 amp rating, of its contacts, will be fine.

 

[Luke'sScreenName]

Thanks whiterose but got this figured out a while back. Appreciate the effort though!

 

[Scrambler82]

lukestaffers,
Was wondering what you have done and how it turned out ?

Just for grins... there are flashing LEDs, you don't need extra pieces just the flashing LED and some wire of proper gauge, ok something, some how to mount it.

 

[Luke'sScreenName]

Yup. The flashing wasn't the problem. I needed to power the strobe when my "control" circuit was open. Hence the need for a relay. It worked! I now have an extreamly bright strobe on my dash when I set my parking break.

 

[Scrambler82]

Ok on the open circuit power.
That's where pin 87A comes in, a useful pin when needed but if not needed it can be a problem.

Sounds good, ltr.