VW Vortex - Volkswagen Forum banner

Is there any difference between an LED testlight and a normal bulb one - READ !

923 Views 3 Replies 4 Participants Last post by  jorge r
I'm thinking a test light is a test light is a test light. However, I don't know everything so in this case maybe it needs to be an LED testlight. The VR won't catch when I crank it so I'm trouble shooting with my trusty bentley. I just finished testing for "ground signal" on the harness for the coilpack. The Bentley calls for using an LED testlight. I only have a bulb powered one and the light doesn't come on when it should , is that because its not an LED ?
1 - 4 of 4 Posts
Re: Is there any difference between an LED testlight and a normal bulb one - READ ! (Lexi)

go to radio shack, buy just one LED bulb, and use the small wire leads to test the circuit you are trying.
their is a BIG difference between a light bulb, and a Light Emitting Diode. first of all, a diode only lets power go thru one direction. its like an electrical one way check valve. secondly, a LED consumes very little watts. i am sure there is a reason the book told you to use a LED over a regular bulb.
good luck.
Re: Is there any difference between an LED testlight and a normal bulb one - READ ! (g60-inside)

Also, the resistance value (ohms) is quite different between LED's and "regular" bulbs.
Some circuit testing needs the eazy current flow an LED would offer. Some need the higher resistance an incandesent bulb has. (such as an older turn signal flasher relay)
In your case, there may not be enough current in the circuit to illuminate the bulb, even if the circuit is live. The LED would light at a MUCH lower current.

Modified by Charles R at 11:23 PM 6-29-2003
Re: Is there any difference between an LED testlight and a normal bulb one - READ ! (Lexi)

An led reacts intatly while a tungsteng or incandescent bulb takes a moment to light up. A fuel injector signal in miliseconds will not light up a tungsteng bulb. A signal to the ignition coil is also in miliseconds and wont light the tungsten bulb.
The led is a diode, it conduct current one way and not the other, unless you have a two color led, it lights up one color with one polarity and another color when polarity is reversed. The led is electricaly rated in milliamps it can conduct, usualy 40-60 miliamps. A diode being like a conductor, no resistance, needs a resistor for it to work before it burns up. Electrical formula states that Volts over Resistance equals Amperes, so a 300 or 400 ohm resistor is needed connected in series with a diode in a 12 volts system (formula:12v/300ohms=0.040amps). This led lamp can be used to test power from the ECM without overloading the ECM and shorting its sensitive circuits.
A regular tungsten lamp or test lamp say rated at 4 watt would consume 1/3 ampere or 10 times the amperes an led lamp consumes. Using this test lamp on the ECM risks oveloading the circuit being tested and burning it up in the ECM.
I just purchased a test light that insted of using a conventional light bulb, it uses an led, it is the cliplead/icepick type, light green and yellow, depends on polarity connection, cool item by my thoughts.
See less See more
1 - 4 of 4 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.