[TR] Moss LED Instrument Lights
tr3driver at ca.rr.com
Mon Apr 28 17:20:32 MDT 2014
> You CANNOT run them in the ignition because of the way that system functions.
To use an LED here, you need to add an ordinary power diode (eg 1N4004) in series with either lead to the ignition lamp. The problem is that LEDs don't like reverse voltage, but the ignition lamp gets reverse voltage every time you turn the key off. The diode is a good idea anyway, as it may help reduce run-on (with an incandescent dash lamp).
For some cars (eg 69 TR6), you also cannot use an LED for the turn signal indicator without making some wiring changes. Again, the problem is that the original wiring delivers reverse voltage to the lamp under some circumstances. In this case you'll need a full wave bridge (which is 4 diodes). Radio shack offers the NTE166 for $1.15 which should work with LEDs but might have trouble if you switch back to incandescent. Or, for a bit more money, use their 276-1181 which should work with incandescent as well.
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