Feb 102015

The green illumination of the dash gauges is achieved by plastic green filters within the gauges. However almost all of these filters had deteriorated due to their proximity to the incandescent bulbs. Some had actually melted due to the heat produced. I had therefore decided to ‘upgrade’ to LEDs after reading the conversion on the E-Type forum. For my conversion, I wanted to:

  • Retain having two brightness settings: Bright and Dim *
  • Switch between green and blue lighting

* – I couldn’t envisage a situation when I would want the side/head lights on but the dash not illuminated. So I have decided to drop the ability to turn off the dash illumination and have replaced the 3-way Panel switch with a 2-way switch.

Dimming the LEDs
The RGB LED strips have a common 12 volt supply and then one wire for each of the primary colours. The LEDs for a specific colour are turned on by connecting the corresponding wire to 0v, ie earth.

The amount of light produced by incandescent bulbs is linear to the current flowing through the bulb. Therefore accurate dimming of the bulbs is achieved by switching a suitably sized resistor into the circuit, in series with the bulbs.

Unfortunately this task is not as simple with LEDs. The light output for two ‘identical’ LEDs is not as predictable simply by reducing the voltage drop across them. The only reliable way to dim LEDs is rapidly switching the LED on and off. Above a certain switching frequency, the human brain cannot differentiate between when the LED is on and off. The perceived brightness is then the relative percentage of time the LED is on during one switching cycle.

Fortunately it’s possible to purchase small LED control units to perform this function. My initial trials using LEDs found that, without on/off switching, the light output was too great. Therefore two LED control units would be needed to control the brightness for both the Bright and Dim settings.

The other key difference, already mentioned, is that the 12v supply voltage is always connected. The individual LED colours are turned on by connecting their earth lead to a ‘floating earth’.

Note: this ‘earth’ is different from the car earth as when in dimming mode it will switch between 0v and 12v.

Green/Blue switching
The ability to switch between green and blue lighting would require the complete rewiring of:
i) the panel switch to select either the ‘Bright’ or ‘Dim’ earth connection from the respective LED control module (rather than provide the 12 volt supply)

ii) the spare switch to then connect the selected earth to either the green or blue lead. After a few trials, I settled on the wiring diagram shown.

Both LED control modules are connected to the loom’s Red supply wire from Fuse 5, which is disconnected from the Panel Switch, and the car’s earth. The positive LED outputs from both control modules provide the 12v supply to the RGB cable.

New wiring is then needed to between the two switches for the earth connections to either the Blue or Green LED lead. Finally the gauges and switch legend LED strip are daisy chained together with 4-core RGB cabling.

Switch Legend Strip
The switch legend is normally lit by three bulbs mounted in convex reflectors approximately 10cm in length. The green hue was achieved by a plastic green tape glued to the rear of the legend strip. However this has faded so it was now more of a mucky yellow colour. The tape was removed as the colour would now be provided by the LEDs.

Green tape provided legend colouring LED strips fitted to legend reflectors
The green colour of the backlighting was obtained by a coloured plastic strip Installation of the LEDs for the illumination of the switch legend.

{Note: the dash photo was taken midway through being cleaned/treated with Gtechniq Trim Restorer C4 – hence the half and half look!}

Dash Gauges
The seven gauges are all opened by rotating the rim until tabs on the rim align with cut-outs in the housing. This enables the rim and glass to be removed to install the LED strips.

The internals of the smaller four gauges (water temperature, oil pressure, fuel and battery) are very similar where the mechanisms are permanently secured to the housing. These mechanisms are quite delicate so the dismantling and insertion of the 10cm LED strips needed to be done with some care.

These gauges have a face plate which has to be eased away from the underlying cup, which has the gauge’s scale printed on it. A small screwdriver can then be inserted under the rim of the cup to prise it away from the housing. Once loose, it’s a matter of rotating the cup to clear the fragile needle.

Six dash gauges and clock Face plate & cup removed LED strip inserted from the rear

It’s very easy to inadvertently solder the RGB earth contacts together so it was well worth testing the operation of the LEDs before rebuilding the gauges.

The clock proved to be more difficult even though the entire clock mechanism comes out with the face. It’s slightly larger than the other gauges and so can accommodate a 15cm strip. However the clearance between the housing and the clock mechanism wasn’t sufficient due to the clear, waterproof coating. This had to be peel off to fit.

Removing the waterproofing Cabling was a tight squeeze Comparing brightness of colours

The entire mechanisms for rev counter and speedometer are also removed with the gauge face, which allows unhindered access to stick the 35cm strip to the perimeter.

Rev counter housing Cable pass through bulb opening Testing prior to rebuilding

The downside of having the ability to switch between the two colours is it requires multi-core cable and so the installation is not so discreet. Even so, it will all be hidden from view once in place.

My first attempt was to use standard RBG cables and connectors but these provide to be temperamental and unlikely to stand the test of time. I therefore changed them to larger plug and socket terminals with internal, mini spade connectors which were also held together by a clip.

RGB connectors were unreliable Blue illumination without dimming Switched to green illumination

The other LED lighting was to illuminated the boot when the bootlid was opened. Two 25cm pure white LED strips were stuck to the underside of the tonneau top panel. Power was provided by running a wire from the permanent Brown fuse terminals and switched by a micro switch attached to the boot hinge.

Would I do the same upgrade again? Definitely not! Possibly just installing a single colour LED strip but the ability to switch between green and blue lighting resulted in unnecessary complexity. Just because it can be done, doesn’t mean it should be done!

 Posted by at 8:43 am
Feb 012013

The map light on the underside of the dash isn’t that bright and so is being replaced by a string of three pure white LED strips; two outer 15cm lengths and a central 10cm length.

I added the middle length in an attempt to make sure the central area, where the standard bulb fitting is located, had equal illumination. The strips are backed with a 3M adhesive tape so it is simply a matter of removing the backing, pressing into place and connecting to the wiring loom via bullet connections.

Heatshrink tubing was used to tidy up the connections between the three strips and hide my dodgy soldering. All that remained was to temporarily fit the dash top to test.

Testing of the Map Light

The minimum order for the pure white LED strip was 2 metres so I had more than 1.5m left over. It seemed a waste not to use it so I looked to see if it could be used ‘tastefully’ elsewhere but was mindful of avoiding making the car look like a victim of a fight with the Halfords aftermarket department!!

A discreet light in the boot, operated when the bootlid is opened, will be covered at a later stage ….

Jan 012013

The backlighting of the dash gauges is provided by incandescent bulbs inserted into the rear of the gauges and is fairly poor by modern standards. The green hue of the backlighting is achieved by coloured plastic covers within the gauges and green plastic tape behind the switch legend strip. However the heat produced by the bulbs had melted several of the covers.

The backlighting can also be set to Bright, Dim or Off via the 3-way Panel Switch. The light produced by these bulbs is almost linear to the applied voltage. When bright is selected, 12 volts is applied across the bulb terminals. While switching to Dim introduces a resistor in series with the bulb. This produces a voltage drop across the resistor and therefore the voltage applied to the bulb and the emitted light is reduced.

One popular ‘upgrade’ is to replace the bulbs by LED strips mounted around the perimeter of the inside of the gauges. LED strips are available either containing a single LED colour group (eg white, red, green, blue, yellow) or all three of the additive primary colours; red, green and blue.

The latter, for obvious reasons referred to as RGB LED strips, can output different light colours by adjusting the relative intensity of each LED colour group. The LED strips also have the advantage that they are more efficient and do not generate a large amount of heat.

The upgrade is well documented in Stéphane’s guide on the E-Type forum. One of the members had tried the upgrade with blue LEDs and I thought this would suit my car, being Opalescent Dark Blue, but I was undecided whether I wanted to lose the original green.

I couldn’t decide which I preferred so I investigated the possibility of being able to switch between the two. In the end I decided to use the RGB LED strips and somehow try to use the spare dash switch (used for the heated rear window on the FHC) to toggle between green and blue. This would lead to numerous problems that would only become apparent as work progressed.

The LED strips currently on offer vary in the number of LEDs per metre; typically 15, 30 or 60 LEDs per metre but also in the strip width; either 8mm (3528 chipset) or 10mm (5050 chipset) and with or without waterproof covering. The aim was to increase the brightness of the backlighting but with the constraint of space within the gauges. So I thought the thinner strips with the waterproof option would be sensible, so I ordered the following:

  • 2 metres (min order) of 3528 Pure White 60 LEDs/m – for the dash map light
  • 5 metres of 3528 RGB 60 LEDs/m – for the gauges

The strips with 60 LEDs per metre can be cut every three LEDs, ie every 5cm. This was ideal as the inner circumference of the smaller gauges would allow a 10cm strip. However the first problem came to light, excuse the pun, when I tested the 3528 RGB strip. This chipset used has one LED for each of the three primary colours in a 5cm strip. When either blue or green is selected, only one of the three LEDs was illuminated. So in the 10cm strip possible, lighting would only be provided by two LEDs – hardly an improvement!

After a few calls to suppliers, it became clear that I needed the wider 10mm strips for the multi-colour option. Each LED in the 5050 chipset is effectively made up of three LEDS; one for each of the red, green and blue colours. So all six LEDs in the 10cm strip would provide light. If the additional width caused a problem I would give up on being able to switch colours and revert back to a single coloured 8mm strip.

While I was planning how to incorporate the upgrade into the existing switch layout I noticed something really odd in the wiring diagrams which I couldn’t understand. The power for the dash illumination is only provided when either the side or main headlights are on. This made perfect sense – if it’s dark enough to need lights then you’d always want to illuminate the gauges. So why did the Panel switch have three settings: Bright, Dim and Off? Why on earth would you ever want to have the side/head lights on and not the dash?

I started to doubt the wiring diagram and so posted the question on the forum. Apparently in the 60s it was a legal requirement when parking at night to have the side lights on. In which case the dash illumination was turned off to conserve the battery. I don’t think I’ll ever need his feature so I’m considering swapping to a two state Panel switch – Bright and Dim.

With the planning done, the next step was to start to dismantle the gauges ….