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Electrical guides and mods

LED Heater Control Lighting

The heater control lights aren't very well lit and colour coding with LEDs isn't ideal. Let's check out the problems and alternatives.

Modification Details

Should The Heater Markers Light Up?

Yes they should but quite often the bulb blows and people question whether they illuminated before.

Where Is The Bulb?

While not immediately obvious, the bulb is actually fitted underneath the safety cluster triangle.
this guide to remove the triangle from the dash so you can access the bulb.

You will find a single BX8.4D twist fit bulb in the centre. Replace with another bulb and test.
The standard bulb is a 1.1w bulb but you can get 1.5w and 2w bulbs which will increase the brightness.

The BX8.4D bulbs are sometimes refered to as 509T or 268 in a base.

Can I Fit An LED Instead?

You certainly can and you should. It took a long time but eventually, suitable LEDs became available.

Remove the button bank, disassemble and remove the original bulb. Click here for that information.

Install the new LED making sure that the LEDs are facing side to side.

They have little wings that help hold it to the board.

However, if you are fitting an LED light of this type to a Roadster, the plastic back plate interferes with the light housing.

As you can see, it doesn't sit flat.

A light tickle with a rotary tool or a file just to open the hole up slightly is an easy fix.

Now it clears the bulb housing fine.

If you are fitting the LED to a fortwo button bank, they bulb base clear it perfectly already.

Plug the button bank back in to test. If the LED doesn't light, pull the LED section out, turn it 180 degrees and plug it back in.

Where Can I Buy These LEDs?

Either look on eBay or order them from smartmods.

The Problem With Light Guides

The initial problem is that the light guide collects light from the side of the bulb.
Standard bulbs illuminate in a very wide beam so light is collected with no problems.

A standard LED illuminates forward so the light guide has problems collecting light.
This means that the collected light is only a fraction of that produced by the LED.

Light guides are very inefficient at carrying light around corners,you can lose
30% of the light through a 90 degree bend, the light guide has two each side.

The final deflection that lights the heater controls will only use about 20% of what it is given.

Because of the pick up point of the light guide and it's inefficiency to carry light,
you can only expect to see about 2% of the light created by the LED.

Everything beyond here is old and not really relevant but I'll keep it here for reference.

So What Is The Solution?

You have a few option to take a look at:

Altered LED Designs

This is a standard LED, they often produce a narrow beam to increase the output.
When used, they usually create a bright spot with no lighting at the side.

The new style flat top LEDs create a slightly wider beam that isn't affected by the done lens.
They create a larger bright spot with no side lighting.

The heater control light guide picks up light from 2 opposite sides so the above LEDs
would not be suitable for usage in that area although some lighting may occur.

What we need is an LED that will emit some side lighting,
currently that only leaves us with the new 'inverted cone' design.

Although the inverted cone design will give better side lighting, it's not perfect.
To get the best from an LED you have to modify it yourself.

If you got a standard or flat top LED and cut a V shaped valley into the top
and then glued a tiny bit of tin foil into the V, it would reflect all the light sideways.

The EL Wire Method


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