2CV dim-dip system removal creit

Credit for the original solution of the dim-dip removal goes to John Wood:

Back in Feb 1995 I wrote to the editor (then Bev Abbot) regarding light switches getting hot, which had been of concern to many drivers of late model cars at that time.

I had noticed my own switch getting quite warm, particularly at the connector where a Mauve wire was attached and decided to find out why this was happening and if I could do anything to cure this problem.

I had just got a new edition of Haynes which had details of the Dim – Dip system which Citroen had cobbled together in order to comply with new regs in UK and maybe in other countries. After studying the new circuit I found that the Mauve wire was carrying all of the current to the lights unlike in earlier models, without Dim – Dip, where the load was shared between two switch terminals and two wires.

I decided to ditch Dim – Dip and return the circuit to standard and set about studying the circuit. After a bit more puzzling I discovered that it was possible to achieve my aim by the deceptively simple method of disconnecting the relays and using a ‘jumper lead’ to bridge connectors 1 and 5 of the plug which has 5 wires going to it. The Dim – Dip Resistor which is mounted on the front cross member of the chassis can also be removed as can the Diode which can be found tied to the Flasher unit under the parcel shelf although this is not essential as they are no longer in the circuit once the relays are removed.

The relays are installed to make the Dim – Dip system work. However, the system is flawed in it’s design, causing the overheating at the switch terminal. Removing the relays enables my method of using a jumper lead to return the circuit to standard to be employed.

Removing a 2CV’s dim-dip system (long version)

With the dim-dip system functionally deactivated and the redundant components removed the final stage was to clean up the wiring loom.

The easiest part was removing the resistor wiring, this was two wires that originated from the joint where the nearside headlight loom connectors emerge.  I cut the wires back to about a centimetre from the loom and put a short section of heat shrink over the exposed ends to tidy them up.

2CV dim-dip resistor removal

The relays were a bit more complicated as two wires needed joining and the rest removing.  To make sure I didn’t remove the wrong wires I started by joining the two wires with a lineman splice and then solder before wrapping up with insulating tape.

2CV dim-dip relay removal

The rest of the wires were then taken back to the loom and covered in heat shrink as above.  (There is also a fly lead that connects the two relays to each other which comes away with them when the rest of the wires are cut.)

With everything neatly tied back there is very little evidence of the dim-dip system left.

Other posts in this series

  1. 2CV dim-dip system overview
  2. Removal (quick version)
  3. Removal (medium version)
  4. Full removal

Removing a 2CV’s dim-dip system (medium version)

With the dim-dip system having been functionally deactivated by removing the relays, I now turned to removing the remaining components: the diode and the resistor.

Diode

The diode was housed in a black plastic case cable tied to the flasher unit under the dash.  Given a diode is effectively a one way valve for electricity it says something about the whole dim-dip setup that the connectors on either end were both yellow with a green wire.

2CV dim dip diode in-situ

Removing this was pretty simple: cut the cable tie, unplug the connectors and stash them away under the dashboard.

Resistor

The resistor was mounted on the near-side of the chassis front rail, behind the bumper.  This is presumably so the airflow will keep it cool but it also exposes it to the worst of the elements.  As a result it was badly corroded.

Unclipping it from the chassis mount and then unplugging the connector from the wiring loom extension was enough to remove it.

2CV dim dip resistor

The wiring loom extension was tidied away and will be fully removed later.

Squeezing together the spring clip allows it to be withdrawn from the chassis.

2CV dim dip resistor mounting clip

Other posts in this series

  1. 2CV dim-dip system overview
  2. Removal (quick version)
  3. Removal (medium version)
  4. Full removal

Removing a 2CV’s dim-dip system (quick version)

At the time Judith was built there was a requirement for new cars in the UK to have a dim-dip system. This was to ensure that when driving on side lights the dip beam of the headlights was also on but at a lower intensity than normal dip beam. Whilst a 2CV’s electrics are normally very simple, the dim-dip system was a bit tortuous requiring the addition of two relays, a diode and a resistor.

2CV dim-dip system circuit diagram

[Note that the colours of the wires can vary, the colours shown in the above diagram are the colours I found on Judith which differ slightly from the colours in the Haynes Manual for 1967-1990 A-series cars and from the wiring loom I used for my Burton.]

To restore the system to original operation both relays and the resistor need removing and the wires to pins one and five of relay one need connecting.  Credit for this discovery goes to John Wood who first published it in 1995 in an article in the 2CVGB magazine.

A full fix for this would involve taking the relay wires back to the main wiring loom and finishing them off properly. This, however, will take a lot of time and require the kind of access given by taking off the wing – not really feasible at the moment.

Given the main thing to achieve is shorting pins one and five of relay one I put together a short jumper cable with two spade connectors. To err on the side of caution I used some 200A headlamp wire but, depending on the headlights you’ve got fitted, you should be able to get away with a lower rated wire.

2CV dim-dip relay shorting jumper cable

The underside of the relay has the pins numbered and, if you clean it up and look really closely, the pins are also marked on the connector.  For the avoidance of doubt, it’s worth triple checking you have pins 1 & 5 on the relay, pins 1 & 5 on the connector and the correctly coloured wires.

2CV dim-dip relay 1 with pins 1 and 5 shorted

With both relays removed and this jumper cable in place in the block connector the entire dim-dip system is functionally deactivated.  The full removal can come at a later date.

Other posts in this series

  1. 2CV dim-dip system overview
  2. Removal (quick version)
  3. Removal (medium version)
  4. Full removal

2CV dim-dip system

The 2CV dim-sip system that was fitted as standard for a short time is a nasty hack and can cause potentially dangerous overheating of electrical components.

Credit for solving this problem goes to John Wood.

Original lighting system

In its original form, the 2CV’s headlight circuit diagram is nice and simple – each switch activates a single pair of lights.

Standard 2CV headlight circuit diagram

[I’ve simplified this diagram somewhat: the side light circuit also has the rear lights on it, the dip beam circuit has the fog-light system hanging off the side and there are some dashboard indicator lights – however, none of these are relevant in this context.]

Dim-dip system

In 1997 and 1998 2CV’s were fitted with a dim-dip system. Due to the complexities of the requirement this was achieved by the addition of two relays, a diode, a resistor and lots of extra wires to connect them all.

2CV dim-dip system circuit diagram

[The ignition system is  much more complicated than just this switch but, again, none of that is relevant in this context.]

With four switches there are theoretically 16 (24) possible states for this system but there are only three that we need to concern ourselves with:

  1. Side light switch on, ignition off:
    • relay 1 de-energised (3-4 connected)
    • relay 2 de-energised
    • side lights illuminated
    • dip beam off
  2. Side light switch on, ignition on:
    • relay 1 de-energised (3-4 connected)
    • relay 2 energised (3-5 connected)
    • side lights illuminated
    • dip beam illuminated via resistor (dim-dip)
  3. Dip beam light switch on:
    • relay 1 energised (3-5 connected)
    • relay 2 isolated
    • dip beam illuminated directly

The other states are either unreachable due to the sequential nature of the light switch (side light -> side light + dip beam)  or are rendered irrelevant by the isolation of relay 2 when the dip beam switch is on.

Whilst this arrangement does achieve the desired effect there are two significant flaws:

  1. The power for the dip beam (and fog light) are now passing through the side light switch:  this adds somewhere in the region of 100W to a circuit designed for around 30W.  Meanwhile the dip beam switch is only energising a 6W relay. This results in the light switch heating up1.
  2. The return-to-ground for relay 2 is via the main beam filament: when the ignition is on and the main beam is off this is putting 6W thorough them. This reduces the life of the main beam lights2.

In addition to these design flaws, there is the possibility of an additional flaw if the diode from the ignition fails:  In this case, when the main beam switch is on, it will allow current from the main beam circuit to power the ignition even when the main ignition switch is off.

Dim-dip removal

Given these issues the removal of the dim-dip system is advisable from a safety point of view.  From a legal (IANAL) point of view the dim-dip system was only ever required at the time of sale, it has never been an MoT requirement – even if originally fitted.

Whilst a complete removal would basically require a new wiring loom it’s relatively easy to functionally remove the system.  The majority of the original system is still in place, it’s just been re-routed through the relays.

The minimum required is to remove the two relays and connect pins 1 and 5 of relay 1.  This routes the dip beam current back through the correct switch and removes the chance of the main beam current flowing back through the ignition circuit.

2CV headlight circuit diagram with dip-dip removed

The resistor and the diode can be left in-situ since the removal of the relays isolates them.  However, for the sake of completeness it’s a good idea to remove them.

Acknowledgements

The circuit diagram is take from the Haynes manual for 1967-1990 A-series cars which, given the colour abbreviations are in French, I’m guessing has come from Citroen originals.

The instruction to connect pins 1 and 5 is taken from a 2002 guide by Mike Phelan based on an article in the 2CVGB magazine by John Wood. This is verified by my own reading of the circuit diagrams and experience with performing the operation on Judith.

Caveat lector

The colours of the wires are taken from the diagrams in the Haynes manual for 1967-1990 A-series cars and from my examination of Judith – your experience may vary.

Footnotes

  1. When I drove Judith back from York it rained most of the way so I had the lights on and I noticed the light switch was hot to the touch. ^
  2. Before leaving York we checked all the lights and they were in working order but, when I checked again after the drive back I found the near side main beam had gone. ^

Other posts in this series

  1. 2CV dim-dip system overview
  2. Removal (quick version)
  3. Removal (medium version)
  4. Full removal