Td5 D2 electrics - Reverse Light Switch

Operation of the reversing lights is not part of the annual UK MOT test. (update: since May 2018 they are!) Any failure in their illumination is only really noticed when reversing in the dark and usually at a time when you could really benefit from their use.

For a long time, I have often felt that the main use of reversing lights on any vehicle is to alert other road users to the fact that the vehicle is reversing. I mean unless you fit a custom spotlight, the relative low power (usually 21w) of the reverse bulbs is not enough to 'light the way' as it were.

And so it was with myself and HX. It was only when my daily parking routine changed and I found myself regularly reverse parking at night onto a paved drive between gateposts and up to a brick wall that I noticed that the reverse lights would 'flicker' on and off seemingly of their own will!

The operation of the reversing lights is governed by a spring loaded manual plunger type switch mounted high up on the main gearbox casing close to the main gear lever. Here is a photo of it...

When reverse is selected with the gear lever, contact is made with the plunger by an internal extension on the lower gear lever and the plunger is physically pushed in causing the circuit to close and the bulbs to illuminate. 

When the gear lever deselects reverse, the switch plunger is released, the circuit is broken and the bulbs extinguish. All very automatic and maintenance free... until the problems start.

Diagnosis of any problem is easy enough. It's either faulty bulbs, wiring issues or freeplay wear in the ridiculously tucked away, awkward and inaccessible plunger switch.. Guess which one it was.?

The best way to check their operation is to place the gearbox into reverse and get an assistant to observe the operation of the rear reversing lights. It is possible to do this solo, the vehicle ignition needs to be 'on' but the engine must be stationary.

It was observed that both reverse lights would illuminate when the gear lever was moved to select 'reverse'. However, once selected, the inherent springing in the gear linkage and the reverse switch itself combined with any free-play will cause the reverse lights to extinguish as the pressure on the engaged reverse switch lessens.

Moving the gear lever from side to side when reverse is engaged caused the lights to flicker on and off and clearly points to wear in the reverse switch. If some sideways hand pressure was maintained on the gear stick the reverse lights would stay illuminated.

This turns out to be a common problem with the Td5 engine or rather more specifically, the R830 gearbox. A new reverse switch is cheap and easily available. However, it's removal and replacement could truly be a real pain in the neck...

REMOVAL / REPLACEMENT.

Research on the Internet threw up a little homemade video from some guy in New Zealand dealing specifically with the same problem and the removal of the gearbox mounted switch. Easily one of the best instructional vids I've ever seen. He had some kind of a body camera mounted on him as he crawled underneath. There was a real claustrophobic 'get out and get under' feel to it. He ended up having to modify a 19mm spanner in order for it to fit into the restrictive and very confined space between the fitted gearbox and the transmission tunnel.

The inherent ground clearance of the body makes the job possible with all the wheels on the ground, but getting 'eyes on the prize' once under there is not easy.

I had to use a magnetic LED work light and carefully place small mirrors ( I recall even taping one in a suitable position ) to allow a very narrow line of sight to the component. I must admit to enjoying that aspect of the job, and once it was all set up the actual removal and replacement of the component was a doddle!!

Having diagnosed the problem as freeplay and wear in the plunger switch, the solution is two-fold. Either remove and replace the reverse switch with a new one or simply remove the thick 2mm washer between the reverse switch body and the gearbox body...

Removing the washer is the cheap fix (providing of course that it hasn't already been removed) and has the effect of bringing the plunger closer to the gear lever so that when engaged the plunger travels further back into the switch body and holds the circuit closed by applying more force to the plunger.

Either solution requires removal of the fitted reverse switch and that is were the fun really starts...

Rave has a wonderful way of making this procedure look easy. ... To get anything near the above view with it's 'open' access means taking the gearbox out!

The reverse switch body is attached by 19mm nut 'flats' formed onto its body. There is a short electrical loom emerging from the end of the switch body that goes to a nearby connector. The easiest tool to use would be a 19mm open spanner but the location and accessibility of the fitted switch really does work against that assumption. In the end I went for the following. 

Also showing the 2mm thick washer.

The solution I arrived at was to purchase a 19mm 'Crowfoot' spanner and mount it to a suitable ratchet (May also use a small extension /adapter socket). 

Even then, due to the location and angle of the 19mm flats and the proximity of nearby gearbox casing ribs, I was only able to get less then a 1/4 turn. This was sufficient to 'break' the torque and I then used a 19mm ring spanner threaded over the switch body for a couple of turns till the switch could be undone by hand and removed from Hx along with the 2mm washer/spacer.

I cleaned up the switch and tested it's continuity with a multi-meter and as there was no problem, I elected to refit the switch minus the washer and everything worked fine from then on! (Sunday 14th June 2015).

The washer that I removed was a chunky 2mm thick. I got to thinking that it really had a 'spacer' type function as it was made of aluminium, or it could well have been plastic.

THE LIGHTBULBS.

Having sorted the switch out, I decided to upgrade the reverse bulbs to LEDS. .. 

Having sourced an LED alternative it's a simple matter of swapping them over..

I removed the light unit from the rear bumper, this gave me a chance to clean it up while swapping the bulbs over. I did one side at a time and I took the opportunity to compare the LED unit to the Tungsten.

The light output was a lot brighter and 'cleaner' then the fitted tungsten 21w bulb in the other reversing light position.

The other bulb shown above is the rear fog hi-viz. I thought about replacing this also with an LED equivalent..

LED 'bulbs' offer great advantages of power saving/output and longevity over equivalent Tungsten filament bulbs. However they do bring issues of 'light-throw' and 'beam projection' particularly when fitted into reflectors designed for 'point-source' filament bulbs.