The attached document provides Workshop Hints for small horsepower Rolls-Royce cars – Rolls-Royce 25/30 – kindly provided by Bryan McGee. This particular document focuses on rewiring.
Last updated: February 2014
March 2014
Rolls-Royce 25/30
Rewiring- Front and Rear of a Rolls-Royce 25/30 from the fuse box.
Note to editor: Image references in red are those on the Disk
Having recently rewired a 1937 25/30 (chassis GRP29) from the fuse box on the bulkhead, both forward and to the rear, I offer these notes to others who may be contemplating a similar excercise.
Note: The wires between the fuse box and the main facia switches on my car were mainly in good condition and therefore left undisturbed. The car concerned is a four door Touring Saloon, by Thrupp and Maberly of fairly standard construction and, for obvious reasons nicknamed ‘The Green Goddess’.
Image RRrewire-01
After over 70 years of service a 25/30, in the words of a well known specialist ‘has either been rewired or needs rewiring’. The original cables were the best available at the time but after more than 7 decades the rubber insulation becomes brittle and can break down at any time which may lead, at best to a failure to proceed and at worst a fire hazard.
Image RRrewire-01 shows the condition of some of the internal wiring.
Happily, period-style multi-core copper cables, with correct colour cotton braided outer but with modern inner insulation material, are still being manufactured.
Image RRrewire-03 shows old cables entering n/s conduits.
Image RRrewire-04 shows a selection of the new braided cables as installed.
Braided cables are available in 5 sizes from 9 to 65 strands to handle from 5.75 to 35 amps. Colours for the principal routes can be selected to match those in the wiring diagram in the handbook and any extra ones to individual choice.
The advent of LED components promises to bring major benefits to serious users of vintage and post-vintage cars, since they can provide good illumination with very low power requirements thus reducing the load on the dynamo and battery. In this rewire I have, so far, only introduced limited LEDs into the ‘D’ tail lights and number plate unit.
Ross Courtney terminal fittings for the cable ends are still available and provide a near match to the originals.
Image RRrewire-05 shows a complete Ross Courtney fitting and the component parts.
Tip: Prepare a bespoke wiring diagram of each circuit of your work when completed to keep in the car’s record file.
Rewiring a Rolls-Royce product of the Thirties to an acceptable standard is a complex operation and not for the fainthearted. Merely to gain access to the conduits and cables requires a disproportionate degree of dismantling, however this provides a great opportunity to improve the condition of otherwise inaccessible areas.
Image RRrewire-06 shows a typical area which is normally covered and inaccessible.
Much of the work can be carried out by the enthusiast owner who has patience and tenacity. One may tackle a rewire in distinct stages i.e. firstly, all the cables to the front from the fuse box, horn solenoid box, fuel pumps and headlamp dipswitch secondly, the rear brake and side lights and the fuel gauge whereas the shorter and more protected wire cables from the fusebox which run separately to the main fascia switches may be in better condition and their replacement deferred to a later date. This description does not cover the latter exercise.
Part One
Front System – headlights, side lights, indicators, spot light and horns
Flexible conduits within the chassis on each side of the car, parallel to the engine bay, carry cables to the relevant headlight, horn and side lights and terminate within the relevant front ‘dumb iron’ abreast of the radiator. These cables are then threaded up into each pillar bracket for headlight and horn and below the front wing in a copper or lead tube along a stay to the side light. Access to the front end of the conduits can only be made by removing the hidden aluminium covers which shroud the dumb irons.
Image RRrewire-07 shows a dumb iron cover before removal and cleaning
Image RRrewire-08 shows a dumb iron cover lifted off.
The wings usually wholly enclose these covers and thus must be removed first.
( Note: The design may vary between different coachbuilders.)
The wings in turn can only be removed if each vertical pillar is lifted out of the tapered socket in the chassis bracket, after removal of the relevant headlamp and its associated horn.
Rewiring provides an opportunity to include additional hidden cables to provide double dipping of both headlights, direction indicators, front and rear foglights etc.
Note: I elected to dispense with the mechanical dipping with solenoid operation and to use double filament headlamp bulbs instead. Since both filaments are so close to the focal point, the dipping is not very effective.
It also provides a good opportunity to remove the brackets and stays for the wings (fenders) which together with the stone guards can be sent away for sandblasting to bare metal, zinc and top coat powder coated. The wings, now off the car, can be readily repainted if necessary.
Image RRrewire-09 shows underside of O/S wing being repaired
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.
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 is drawn into position by a castle nut below and secured by a 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 are then nearly always called for:
However, first try the following:
Invert the castle nut to protect the threaded stub.
Place a bottle jack under the threaded end of the pillar 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 very drastic treatment to free the taper location of the pillars from their chassis mounted brackets. Copperslip was clearly not used on the original build.
Tip: Fire extinguishers and buckets of water should be kept on hand.
Image RRrewire-10 & RRrewire-11
On my Thrupp and Maberly the front wings extend over the covers shrouding the 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.
Image RRrewire-12 shows pillar refurbished by sandblasting and powdercoating.
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 RRrewire-13 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 Fuse box and Regulator assy.
To gain access to the rear of the fuse box it needs to be pulled away from the bulkhead.
It is held in position by three studs which are held by ¼” BSF nuts, accessible above the foot pedals within the drivers area.
Image RRrewire-14 shows the fuse box moved partially away from the bulkhead.
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 RRrewire-15 shows old wires from behind starter solenoid.
Image RRrewire-16 shows the new cables before completing the refitting of the aluminium trunking covers
Aluminium trunking
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. Image RRrewire-17
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.
Image RRrewire-18 and Image RRrewire-19
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.
Image RRrewire-20 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 RRrewire-21 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 RRrewire-22 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.
See Image RRrewire-23
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.
Image RRrewire-24 shows the O/S front dumb iron being treated for surface rust.
Image RRrewire-25 shows the O/S front chassis area after treating with Waxoyl.
Image RRrewire-26 shows the new cables emerging from the conduit.
Image RRrewire-27 shows a set of wing stays after sandblasting and powder coating
Image RRrewire-28 shows the wing stays refitted to the chassis.
Once the wing has been refitted with new stainless fasteners where possible and the inner edge with wing piping, the headlamp support pillar can be refitted.
A gasket should be cut for the mating faces. The tapered surfaces of the pillar must be clean and coated with ‘copperslip’ to ensure ease of disassembly in future. The cables for dipped and main beam, horn and earth all need to be 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.
Image RRrewire-29 shows a pillar with its new cables awaiting re installation.
Part Two
Rear of Car
The rewire of the rear of the car is somewhat simpler and just needs perseverance.
Most of the cables serving the rear of the car, the supply from the battery and rear body internals run in conduits within the nearside (left) chassis member. The wiring added by the coachbuilders are sometimes quite difficult to access and, due to the careful fixing methods used, difficult to remove without disturbing the headlining etc.
Firstly remove all floorboards and the passenger front seat as well as the boot (trunk) floor to maximise access to the working area.
The chassis members are likely to have accumulated oily dirt over the decades such that a thorough clean with ‘Gunk’ or similar is recommended before starting on dismantling.
It is highly unlikely that it will be possible to withdraw existing wiring in situ and thus it will be necessary to sever the wires as they enter and leave the flexible conduits and then prise the conduits away from their brackets and remove from the car. The cables can then generally be pulled out and the conduits degreased and rust proofed.
Battery Cable
The original cable is likely to have deteriorated and is worth replacing with a new one with PVC insulation.
Two sizes are commonly available: 37/0.9 rated for 170 Amps and 61/0.90 rated for 300 Amps. Both types are also available for the ‘purists’ with braided cover but at extra cost.
The 37/0.90 cable type is probably more than adequate for the ‘small horsepower’ Rolls-Royce and Derby Bentleys and the heavier duty for the Phantom models.
Note: The terminal fitting at the front of the cable to locate in the starter solenoid is a special shape and should be recovered and reused.
Accessories
A circular junction box is fitted inside the chassis member below the rear seat. (in the case of a 5 seater saloon)
Image RRrewire-30 shows the circular junction box.
The coachbuilder concerned took feeds from this to his rear internal switches, interior lights and cigar lighter. The central post is an earth and the four internal terminals are all connected and fed by a live from the main fusebox. All wires from this junction box need to be replaced since they otherwise constitute a fire risk.
On my T & M body there is also a terminal block, in the circuit feeding the rear accessories, hidden behind the headlining behind the nearside rear quarter and covered by the seat back.
Image shows terminal block for distribution of interior wiring
Fuel Gauge
The Handbook provides a full section on the Smith Electric Petrol Gauge in which a wiring diagram for the connections between the tank instrument and the back of the meter on the fascia is provided. A four core cable is required but, since the current in each core is very tiny, it is possible to source a seven core cable and use only four of them.
Flashing indicators
If it is proposed to add flashing indicators and retain the trafficators in working condition, Messrs Autosparks can provide an effective circuit diagram which incorporates two flasher relays in order to operate both systems in parallel.
Rear Lights
I took the decision to remove the non-original stop/tail light units from the rear wings, which had been fitted in the ‘50s, and thus restore the wings to their original clean shape.
Image RRrewire-31 … showing 1950s light unit removed.
I then added SVC reproduction period style lamps for Stop/ Tail / Indicators onto brackets fixed to the rear bumper so that they could be readily removed at a later date, if ever required. Lucas reversing and rear fog lights are also bumper bracket mounted.
What to do with the lovely ACE number plate unit with its two ‘D’ lamps ? I elected to bring it back into effective use with minimal additional electrical load by the use of the latest LED components. The housing components were all taken back to bare metal and repainted before reassembly then new bulb holders were fixed behind the ‘D’ lenses into which LED bulbs were inserted. A strip of white LEDs was fixed behind the translucent numberplate which provides excellent back illumination for the letters and numbers.
Image RRrewire-32… showing two LED bulbs and strip behind number plate
Image RRrewire-33 … shows completed ACE unit and complementing SVC lamps.
The overall effect on the appearance looks authentic but the additional electrical current requirement, and thus load on the dynamo, is very small.
References:
Handbook of the 25-30 Car (Chapter VIII in the full edition, Chapter VII in the Condensed Edition).
Suppliers
The following are some of the available suppliers in Britain of the components required for rewiring and updating the electrical systems of these models. Suppliers of similar components are available elsewhere in the world.
– Braided cables etc – Autosparks www.autosparks.co.uk
– Halogen bulbs and holders – Paul Goff www.norbsa02.freeuk.com
– LED bulbs – www.dynamoregulatorconversions.com
– Ross-Cortney cable terminals – D.H. Day, Swindon-dhday31@hotmail.com
– Fuse carriers (flat) – Avenue Mail Order www.avenuemail.com
– Single fuse unit – Tim Hodgekiss www.vintagemotorspares.com
– Reproduction tail lights – Staffordshire Vehicle Components www.s-v-c.co.uk
– Flexible fuel hoses – Flexolite www.flexolite.co.uk
Acknowledgements
The writer wishes to acknowledge the help and advice received from Messrs Stephen Wragg and John Hibbert, fellow owners of 25 hp cars, without whose help the task could not have been undertaken.
Disclaimer
These notes have been compiled in good faith and are offered to other members for information only and they do not represent official policy of the RREC or imply any warranty whatsoever.
Bryan McGee bryan@bcmcgee.co.uk February 2014
RR.RewiringFrontandRear.08.13.doc
