Manulat

Just replaced the backlighting on the panel lights with LED bulbs. Some bulbs did not light up first. I check the fuse and tne panel light 7.5 amp fuse burnt. Then I turn the bulbs around to correct the polarity and reconnectd the connectors. I then put temporarily 15 amp fuse. Every thing worked fine until now. The instrument lights up on the first click but when you click it to the second and third, to use the headlight, the instrument lights and the panel backlights does not work. I already replaced the fuse with 7.5 amp (THE SPECIFIED ONE) and still the same problem. I took the panel light fuse and the instrument lights worked fine as normal but I'm not getting any panel backlightsl on the center console where the stereo, climate control and shift lever back lights are.

Can someone help me with this ??

oldskewel

iTrader: (1)

I don't know about converting to LEDs, but on my '91, here's how the panel backlighting works:

- when headlights are off and the components (climate control / radio) are on, the LCD and button-light (the green lights on the climate buttons) backlighting is on at full brightness.

- when headlights are on, ... the LCD and button-light backlighting is on at a reduced brightness level, and button backlighting (not the green lights on the climate buttons, just that the buttons light up slightly) turns on.

I assume the light output is reduced by reducing the voltage applied to the bulbs. My understanding of diodes in general (the D in LED) is that they act as an open circuit below some voltage threshold (e.g., 3.5 Volts for a white LED), then pass current with that voltage drop. A ballast resistor can be placed in series with the LED if the supply voltage is significantly higher than the nominal voltage drop. (this is all from memory of a freshman year class almost 30 years ago, so consider it general, and perhaps outdated info)

To summarize/translate, my guess is that the Lexus panel lighting dims the lights when the headlights go on, as designed, dropping the voltage to the bulbs below the LED threshold. So for a regular bulb, it dims, but for an LED, it turns off.

One thing to try is to adjust the **** for instrument panel brightness (to the lower left of the instrument panel, next to the security light on my '91). Turn it all the way clockwise until it clicks. This sets instruments and panel brightness to not dim when the headlights are on. That may rule out some things for you while you track down any other blown-fuse issues you might have.

Manulat

Looks like its acting opposite. I drove today and the lights were working but when I pass under a bridge the lights turns off and back on after passing the dark space. Then when it was completely dark (night) the lights including the instrument cluster turned off and no lights at all. I've checked all the fuses and they were all O.K. Strange!! I took the panel light fuses and the cluster lights turned on but no panel lights. Again it makes me crazy.

Manulat

Finally solved the problem. It was caused by dying battery. Replace the battery and it works perfect now with the LED bulbs. Thanks to you though OLDSKEWEL.