how to wire a 12v light to a led circut

or would this reed relay be better? http://www./itm/0-5-Amp-SPST-Reed-Relay-at-12VDC-2160388-/150888992653?pt=LH_DefaultDomain_0&hash=item2321af4f8d

If it is brown, red, black, black then you are looking at an R of 120 ohms. I = 5/120 = ~41mA. However, like I mentioned before, and a quick Google search verified, the actual pin can only supply 25mA of current. I couldn't get the link to the SSR to load. I, personally, wouldn't use an SSR as you are trying to power a low current device. SSRs are known to have a small leakage current that may cause the light to light dimly when not in use. My recommendation would be to use a 5vdc reed relay. It has a coil that will draw minimal current and has a set of contacts that will be perfect to power your 25mA device. http://www.radioshack.com/product/index.jsp?productid=2062478Kevin Pierson

1redvert wrote: or would this reed relay be better? http://www./itm/0-5-Amp-SPST-Reed-Relay-at-12VDC-2160388-/150888992653?pt=LH_DefaultDomain_0&hash=item2321af4f8d

You need a 5vdc reed relay, but that is very, very close.Kevin Pierson

sweeet that's what I've been looking for is the right one and they have that one at my local radio shack down the street. (i live in the mountains and they never have anything i need) ok now all i have to do is replace the led with the coil of the reed switch and wire the contacts of the reed to the led strip right. I really like electronics and would love to take a class to expand my very limited knowledge...thanks for all the help

the reed relay i got says 250 ohms do you think i will need to change or remove the resistor that is before the led? or just soldier it in and not worry about it?

I'm assuming they are talking about the coil. That will give you a 20mA draw. That should be fine for your application, although it is approaching the upper limit of what the pin can safely supply. However, since it is a shift light and the actual "ON" time should be very low, it should be OK. The resistor is in line to limit current to prevent damage to the pin. When you add the resistance of the new coil in series to the existing coil it will limit current too much. You will need to remove (or bypass) the resistor on the board for that relay to work.Kevin Pierson

great thanks, thats what i was thinking as i was looking at it. I am just learning about resistors and leds because i wanted to put custom green leds in my Porsche 911 gauges. i will try and work on it later tonight and get it installed by this weekend. thanks again for all your help.

I was trawling the internet for help and i came across this thread, so i thought i would resurect it. I have just bought the same style shift light although a much updated version looking at the difference in the circuit boards.... my (probably stupid)questions are, how does this shift light work? you adjust the knob to what rpm you want the light to come on, but how does it know?? secondly, the output to power the LED (has been cut off in the pic, l/h side) is only 5v. is it possible to increase the output to 12v to power an external led that i already have, or will i just need to replace mine with 5v led's? TIA

Most modern shift lights measure frequency of either an injector or coil (or other pulsing signal that changes in a linear fashion with RPM). The pot is most likely creating a 0-5vdc signal that is going back to a processor that is converting the analog voltage to a digital representation and then comparing that value to the measured frequency. If the frequency value is lower than the voltage setpoint the light comes on. You could add a transistor inline with the output to drive your 12v LED.Kevin Pierson