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?