Dash lighting using SMD 3528 and SMD 5050 LEDs

Background: A couple of years ago my rheostat was burning my tachometer so I bypassed the rheostat and changed to LEDs bulbs but the light output from the LEDs was not very impressive. Since my dashboard was removed for an interior refit, I decided to try some of the newer multiple-SMD LEDs to get better results. I posted the results from my trial and error yesterday and was asked to post more details so here they are.

The speedometer, small gauges and tachometer are all backlit differently. The speedometer is lit by two T5 wedge bulbs shining directly through a close-proximity blue filter and diffracted/reflected through a clear circumferential ring onto the gauge face.

The small gauges are lit by a single BA9 bayonet bulb diffracted/reflected through a blue circumferential ring onto the gauge face.

The tachometer is lit by two BA9 bayonet bulbs shining through a close proximity blue plastic filter at the back of the housing with no circumferential ring to redirect the light onto the gauge face at the front. This explains why the tachometer is never lit very well.

Putting all the same intensity bulbs in the gauges gave an uneven output. The small gauges have the best backlighting design and the tachometer the worst. I found the light output most balanced if I used smaller SMDs in the small gauges and larger SMDs in the tachometer.

The speedo had a different issue... Mine had a clear diffraction ring and that seemed to give a different hue to that gauge. I don’t know if that was standard or not. Regardless of which T5 LED I used the colour did not match the other gauges. In the end I disassembled the speedometer and hand tinted the ring with a green/blue dry erase marker. It is not perfect so I will probably remove it and airbrush it to get a perfectly even colour output.

Finally, not all the BA9 bulbs in the dash can be replaced with LEDs. Some of the warning lights are reverse polarity. For example my oil pressure light was wired up backwards. Of course that does not make a different to an incandescent bulb but an LED being a diode won't work reversed. Some are supposed to be bi-directional but that was not what I found. Therefore for the warning lights I generally stuck with incandescent bulbs unless I could easily test the polarity was correct for the LEDs.

Finally, finally I read somewhere that using an LED in the 'G' light from the alternator might affect the alternator operation so I kept that incandescent as well.

The LEDs I used were:

Speedometer: 2 x T5 LEDs using single 5050 SMD (5050 because it is 5.0mm x 5.0mm). Bought from Ebay seller ‘cna2015’.

Small gauges: 1 x BA9 LED using 10 x 3528 SMDs (3528 because they are 3.5mm x 2.8mm). Bought from Ebay seller ‘cenn2010’.

Tachometer: 2 x BA9 LED using 5 x 5050 SMDs bought from Ebay seller ‘ceresimports08’. These are a tight fit in the bulb holder since the corners of the SMDs stick out. They do fit though but when extracting, do not twist or as they can fall out inside the tachometer requiring disassembly to extract.

Regards
David
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