Image shows a dumb iron cover before removal and cleaning

Procedure

Jack up the front of the car and secure on axle stands.

Remove the relevant front wheel and wrap the exposed greasy splined hub with a plastic bag and elastic  band or similar.
Remove the headlamp and horn concerned, having disconnected the wires, and stow safely.
Remove the under-wing stone guard to provide access to the stays.
Remove the main stay which encloses the outrigger support for the pillar bracket.
 4 – 5/16” BSF nuts to undo on the chassis.  See image DSCO5082
Remove the vertical pillar  which supports the headlamp and horn.
This pillar  locates into an outboard bracket on the chassis on a double taper and below is held in position by a castle nut and split pin.
Remove the split pin and undo the ½” BSF nut.
Strike the end of the pillar  upwards with a mallet.
Almost invariably this taper has seized and no amount of normal effort will free it.
Extreme measures may then be called for:
However first try the following:
 Invert the castle nut to protect the threaded stub.
 Place a bottle jack under the bracket and jack up until the weight of the car is taken on  this stub
 Tap the outrigger bracket housing with a mallet or hammer in the hope this will release the tapers.
 If this fails, then extreme heat may be necessary to expand the housing and free the tapers.
A conventional blow lamp may not be sufficient and the use of methylacetylene-propadiene gas (MAPPS) should be considered in order to bring the housing to red heat.
All  three cars we have recently worked on have required this drastic treatment to free the taper location of the pillars.
Tip: Fire extinguishers and buckets of water should be kept on hand.

On my Thrupp and Maberly the wings extend over the covers shrouding the front dumb irons and each is secured by three horizontal spacer rods which have slotted mushroom heads.

To remove these rods undo the ¼” BSF nuts on the outboard side of the chassis members and tap the rod ends with a mallet to free them.
The stays for supporting the wings are generally in poor shape and benefit from being sent away for sand blasting and powdercoat repainting to give a durable finish. The original bolts for fixing the wings to the running boards and to the stays etc can usually be discarded and replaced with stainless ones which will minimise preferential corrosion of the aluminium contact  parts. Mass produced 6mm and 8mm metric fasteners which are economical to source might be deemed acceptable in these unstressed and hidden applications.

Tip: Stainless threads should  be greased before tightening to avoid thread galling and possible seizing.

Chassis side members

The flat aluminium plates covering the side members should be removed to allow cleaning, derusting and waxoyl treating of the side member below.
Image shows underside of a plate.

Conduits

The flexible metal conduits may be externally sound but it is unlikely that the existing cables can be drawn out and/or new ones installed in situ. The removal of the front wings improves access to the clips to enable the removal of the conduits, having severed the wires at each end. After a thorough degrease and clean the original conduits are often suitable for reuse.

 Main Starter Switch (solenoid)

The starter solenoid located on the N/S lower bulkhead  is held by three screws accessible from the passenger footwell. Most of the cables serving the near-side of the car are routed behind this assembly which necessitates the release of it from the bulkhead to gain access for running the new cables.
Image shows old wires from behind starter solenoid.

Aluminium trunking

Image shows the new cables before completing the refitting of the aluminium trunking covers

The trunking all needs removing to access the cable runs. The cast alloy joining sections are fixed to the bulkhead with square headed bolts with 3 BA nuts

Isolating switch

If none is fitted, the rewire provides a good opportunity to fit isolating switch(es).
Firstly, a battery isolation switch can be most readily fitted below the rear seat to isolate the negative terminal of the battery from the chassis earth. A proprietary low amp in-line fuse unit, say 5amp, can also be wired between the negative battery terminal and the chassis, thus bypassing the battery isolator switch to ensure a continuous low amp supply for accessories.

Since this will not be convenient for daily use, consideration can be given to fitting another switch on the feed to the main fuse box ( fuse 8) The cable to this comes from the positive starter motor cable from the battery and emanates from the top of the Main Starter Switch (solenoid) and runs along and within the horizontal alloy trunking. If purists allow, one can drill the bulkhead to divert the new cable out above the passenger footwell, through a switch and then back into the trunking to connect with the lower terminal of fuse 8. 
If the electric clock and/or trickle charge socket is to be kept alive, they can be fed from the live side of this isolating switch via a 5amp fuse unit.
Note: Tim Hodgekiss can supply a nice period style Lucas type single fuse unit.

Note: Also visible in the picture is the end of the new fuel hose  which is resistant to attack by modern fuels and covered by braided stainless steel as made by messrs Flexolite. Since the fuel hose is above the exhaust system any leak would constitute another fire hazard.

mage shows the battery trickle charger plugged into the former cigar lighter socket.

Headlights 

25/30 models are usually supplied with Lucas P100 type headlamps. The reflector of the near side unit  pivots so that in the ‘dipped’ mode the beam of  light is directed downward. The off side unit has a fixed reflector and extinguishes when dipped. This arrangement is highly unsatisfactory for modern driving conditions. It is therefore recommended to fit both reflectors with new double contact bulb holders and double filament halogen bulbs.
Image shows the removed pivoting reflector and the new bulb holder and bulb awaiting fitting.

Front Sidelights

Some 25/30 cars are fitted with the large ‘torpedo’ sidelight housings. It is possible to convert these to carry two 9mm bulb holders, one holder to take a 23W amber bulb for direction indication and the other a 5 or 10W halogen bulb for the side light.
This obviates the need to mount  less elegant independent modern amber lamps on the bumper assembly or elsewhere. The extra cable for the indicator can be run up under the wing together with the side light supply. A common earth wire can be run from the lamp housing back to the chassis.
Image shows the pair of bulbs and holders for the O/S torpedo light housing.

Horns

The two, yellow and green,  insulated cables for the Loud and Soft horn activation run down a small bore in the steering column and then to a very inaccessible junction box within the O/S chassis frame. There they connect to the green and yellow braided (suggest 9 strand type) cables which run through conduit and trunking to the horn Relay located alongside the Regulator. From the Relay the increased current to the actual horns is carried in blue braided 14 strand cables (rated 8.75 amps).
Note: Each of the fine pvc insulated cables within the steering column cannot exceed 2.5 mm O.D. due to the space limitation.
Tip: To draw the new thin cables down the column join the end of each cable and solder the two to a single ‘pilot’ wire which can be fed down the column and by pulling it through one can draw the pair of horn wires through. In order to ease this, talcum baby powder can be sprinkled on the cables to dry lubricate their passage down the column.

Fuses

Most of the fuses are of the so-called ‘flat’ type in which the fuse wire can be readily replaced. According to the handbook, all of the fuses apart from the ‘battery emergency’ fuse are a single strand of No 30 S.W.G. copper wire. Standard domestic fuse wire, which is readily available, can be used if necessary. The dynamo field fuse is a 4.5 amp glass cartridge type. If none is available a standard domestic 5 amp fuse can be used on a temporary basis.

Reassembly

The stripping of the front of the car provides excellent access to otherwise inaccessible areas and thus a chance to clean and prepare for reassembly

A set of wing stays after sandblasting and powder coating

Once the wing has been refitted with new stainless fasteners where possible and the inner edge with wing piping, the headlamp pillar can be refitted.
A gasket should be cut for the mating faces. The tapered surfaces must be clean and coated with ‘copperslip’. The cables for dipped and main beam, horn and earth all threaded through their respective inlets and outlets. Only then can the pillar be offered through the wing aperture all the while drawing the cables taut. Once the tapers on the pillar have mated with those in the chassis bracket the ½”BSF nut and washer can be loosely tightened.