underbonnet wiring runs

This post has been in drafts for over two years and continues from this post! Easiest to post now and alter/develop/clarify further in response to owner comments. Thanks to all who have participated with this so far…

The wiring runs changed significantly between the early 1933 cars and the later Nippy. Identification of cars is made easier by the presence of the holes on the firewall and bulkhead. Even if obscured, remains may still be seen from below the dash.

Phase 1: CF3 cut-out

Very early cars – here 178xxx – had the CF3 cut-out with 4 terminals and the early C35A dynamo with a separate resistor box on top. Characterised by separate wiring cables clipped with black bakelite flat clamps with two slot head machine screws, directly beneath and in line with the cut-out, in a row up the bulkhead from near the throttle bar.

NO round junction box visible, but one was found present UNDER the dash and used for headlight wiring. The last photos shows the bulkhead from the underside, with the arrowed route of the cable cluster coming up to the junction box. No grommet entering the rear of the O/S dash cubby hole.

This is the chassis number directly preceding the car above, showing the parallel lines of clip holes quite close to the raised section, and the remains of the separate box on the C35A :

This one is earlier than both of them – 177xxx – (but has lost its vertical gusset plates during restoration, and now has a later CFR control box):

On early cars with vertical gusset plates (here Nick Boorman’s 65 pre-restoration), the N/S headlight wiring runs through the interior under the dashboard, emerging from a grommet into the N/S engine bay. (On the right, armoured cable from the back of the car can be seen clipped in at the top of the photo, coming to the petrol gauge).

The green arrows show the double saddle clip (as per BD237 below) on the front face of the battery box with the vacuum tube; and the glint of light from strangler wire or clip hole – the cable exit would be further over to the left and a bit higher in this image.

The large grommet is shown below at the very top of the photo, with single clips present on the bulkhead face, solely for the battery cable from the starter. Offside and nearside lighting runs were in half saddle clips attached to the wing top bolts. Offside then follows black cable clamps up the firewall and through bulkhead between tool box and cut out.

Note in the picture above the earthing point is on the lower face of the bulkhead, and the main access point for wiring exiting to behind the dash is in the upper face.

Car 179xxx is directly before the alterations advice in the timeline, but Sports models may have happened slightly later, as this car starts to show an external N/S headlamp loom run:

A cutout change was made at 179368 (22nd August 1933), which equates to about EB body 70.


Phase 2: CFR cut-out – (circa) 1934 registrations onwards

The CFR cut-out now contains the resistance that was on the top of the dynamo on the earliest cars.

This ’65’, 190xxx shows a more developed loom and the wiring for the N/S headlight has come onto the front of the bulkhead, running above the tool box and down through the new horizontal gusset plate. The bakelite clips under the cutout still continue.

This car, unknown chassis (do you know of it?) but probably late 1933/early 1934 as it follows the route of the car above, but with the exception of the cutout being moved over to the right, away from the line of the original loom bridge clips:

This car 197xxx, one of the first Nippies, has evidence of the clip holes for an upper wiring run above the tool box line.

200xxx; largely unoriginal layout but evidence of top clip holes on the top face…

This 1934 car 201xxx shows the CFR, old style junction box and fuse box and also has evidence of wire clips across the top of the toolbox area.

This 1935 car 216xxx also shows an original junction box design shown in all the illustrated Austin parts lists 1934-38 parts catalogues. It was replaced by the more rounded Lucas 4J item (one seen above on the vertical face of the firewall).

This 1935 car 219xxx (below) has an unoriginal later CFR2 with 6 terminals, and the unit is slightly wider. The CFR would have sat within the right hand space of that pictured. Note the new grommet/hole for access to the back of the cubby hole, the position of a new junction box for the wiring coming from the steering wheel central functions, the earthing point (reinforced with a steel grommet) moving UP to the top face of the bulkhead, and the main hole giving access to the back of the dashboard moving DOWN to under the control box.

All three 1935 cars (the two images immediately above are the same car as the picture above both) have NO evidence of holes across the top of the toolbox area for N/S headlight wiring and have evidence of the double clip (arrowed) on the firewall for the parallel lower run with the battery lead.

The fuse box and 4 junction Lucas box were present throughout the post-65 run.

Chassis 220935 – amendment “headlamp with cable harness” April 1935

As the two 1935 cars show no upper cable run, could this Index card signify the move to a different position for the N/S headlamp shown in later cars below? Or could it have been in the next change at 230952?

Car 230xxx – top run clip holes visible in largely unscathed metalwork:

Chassis 230952 (September 1935)  – amendment “changes to CFR2 and C35M dynamo and wiring harness” 

Phase 3: CFR2 cut-out  – September 1935 (circa 1936 registrations onwards)

Chassis 236210 (December 1935; 1936 registrations) change to positive earth


This 1936 car 245xxx seem to have a lower run (in unoriginal wiring) for the N/S headlamp wiring, in parallel with the battery cable to the starter. Need to check for hole evidence in the upper area.

1936 251xxx upper route; junction box used for headlamp wiring

N/S lighting loom over the top of the toolbox

1936 252xxx upper route

1936 LHD car 255xxx evidence of upper route and/or clip holes

1937 car 265xxx – thought to be largely original as it was stored from 1954 after a crankshaft break – shows

leather loom clips on the upper bulkhead, previously found by Chris Gould on his slightly earlier car:

The oblong strip of leather is 3.4″ x 0.7″ x 1/8″. (approx 18mm wide x 3mm thick)

Secondly, the N/S lighting bundle running along the front of the bulkhead again, in parallel with the starter to battery cable and double clips:

The wiring from the steering column (4 wires in trafficator cars) is in a single 4 core cable separate from the loom. A disassembly break point is the Lucas junction box where the wires join with the loom. You can see the cut off end of the 4 core cable here:

There are no breaks in the presumed-original 1937 loom for wiring to the side/headlights (seen here with a bespoke item created by Autosparks to reproduce the Nippy loom) :

The two bound wires heading back from the top central grommet on the firewall above the toolbox are for the horn and emerged from the grommet to run along the bonnet centre support:

Open questions:

Why does this later car return to the early wiring route? We need to find other late cars.

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