Fog Lamps

 One of my rear fog lamps had snapped off and was hanging by the wire. I dont recall any incident that could account for this, but they are vulnerable hanging below the car and exposed to spray and weather. Mine was probably broken in the process of removing the car cover so  I'll need to be more careful in future.

My remaining fog lamp

 However this also underlies the main cause of the weakness as the need for corrosion resistance means that these lamps (Lucas 921) have plastic bodies. Some have a chrome-like finish, but are still plastic underneath. They tend to crack around the mounting point where they vibrate. This is compounded by what I'm calling bad design as well. The lights are mounted by a single captive bolt protruding through the back of the lamp. The stud then passes through the mounting bracket (rubber washer mount) and is secured with a nut and washers. This arrangement is fine for securing a new lamp, but the securing nut is exposed to the elements and its bound to corrode. It WILL weld itself solidly to the stud. This means that if you try to undo the nut, the whole lamp will simply rotate. The natural response to this is to hold the lamp as you unscrew the nut... DO NOT DO THIS. The bolt head is captive inside the lamp, but the lamp is plastic so its only weakly held between moulded plastic lugs inside the lamp body. Holding the lamp and then turning the nut means the whole bolt will rotate inside the lamp and its head will mash the plastic mouldings inside the case and probably crack it! 

Intact foglamp before removal- note the bulb contact wire (Gr/R) penetrating the case and the earth contact (top left) attached to the mounting bolt.

In my case the lamp had broken and was no longer attached to the body bracket - I cut the wires to release it- note the earth contact- from rear of fog lamp.

If you need to remove an old lamp (that is actually still mounted to the body) proceed as follows: Remove the 2 screws securing the reflector and remove it- care with rubber seal. Note the two rubber washers that cushion the screw holes.

Ease the green/black wire passing through the body of the lamp through its grommet and further into the lamp. You can then slip the white bulb holder forwards and out of its grooves. This is necessary before removing or fitting a bulb as there isn't enough room inside the lamp to do this. Remove the bulb.

Bulb holder slipped right off. Note rear bulb body contact below nut.

You will then have access to the bolt head in its moulded recess. There should be enough room to slip a small socket (1/4" drive) on an extension onto the nut, but as this is recessed it can be awkward. A slim box spanner might be more successful? In my case the rubber mounting washer behind the lamp had disintegrated and I could pull the remnants out. This gave the mounting bolt some movement and I could pop the bolt head up inside the lamp by pressing it in from the rear. Using a third hand grip the rear nut with a ring spanner and unscrew the bolt using the two spanners against each other. This is awkward, but should avoid damaging the lamp.  

Note the shake proof and flat washer fitted to the rear of the lamp and the electrical earthing wire. The bulb body contact inside the lamp will come out with the bolt, note how this should be fitted (protrusion forward and uppermost). One of my lamps also had a square copper reinforcing plate under this contact but I don't know if this should always be present.

Inside of lamp.. all fittings removed. Note moulded plastic lugs far too weak to to hold the bolt head

When refitting fit the lamp before replacing the bulb. Clean up the mounting bracket and treat it and the contacts to some dielectric grease. Put some corrosion-block or copper grease on the mounting threads. Use a new rubber washer and refit the lamp; the order is (from the car towards the lamp); Nut, shake-proof washer, flat washer, (mounting bracket), earth tag, rubber washer, (lamp body), internal contact, bolt head.  Fit a new bulb and slip the white holder onto its contacts. Pull the excess wire out of the lamp through the grommet.

Fog lamp refitted

Refit the red lens and don't forget the rubber seal and the two thin rubber washers on the screw holes.