LED Scanner

The only scanner wire going to the alarm should be the yellow one. The red wire should go to an unswitched +12v and the black wire to ground.

 tried that still will not work.  I put the yellow and black together.  The light will come on , but only with the button on the scanner.  Someone else with the same led.  told me they have 5 and could only get the  led to work with the black on acc, red to constant, and left the yellow off.  Meybe the yellow is no good on my scanner.  How can I check??? I went to the dealer today, but it will cost me 1.5 hour labour.  Not worth it. That is more than the scanner.

What's the scanner's make/model number?

 CLA , but I do not have a model number.  I think it musty be the yellow wire.  Like I said if I hook the red to constant 12v the yellow to ground it lites, but vary dim. (almost off) black not hooked up.  I tried this on a varying 12v dc adapter.  When I turn the swithch down it will no longer lite.  So, what do you think.  -500ma not enough.  Would a relay increase the output of the acc wire on the alarm?

To test it,hook up the yellow and black wires together to ground. If it doesn't work, then the scanner is faulty.

 It works like that, but I have to push the button on the scanner.  It will not turn on otherwise.  Is that what you mean????

Some scanners come preprogrammed with several patterns, perhaps you need to set it up. Did it come with a manual?

 no, the instructions where on the box.  But they were basic red-posotive, black-negative, yellow-alarm acc.  talked to someone with t5 of the same scanners, but they hooked theres up as follows, red-posotive, black-alarm output, and left the yellow disconnected.  He said this was the only way it would work.  Mine must be garbage.  I guess.