40 SS wiring layout

From the parts book the main chassis cable harness correct for my car '40 SS is 970442 (same thru to chassis Mark IV #510412)
The main body cable harness is 990481/B (same thru from 510001. All Mk IV)
My question is would this have had the flexible steel conduit covering them as did the earlier '39 cars or not?
If I were to look for evidence of the steel conduit could I expect to find retaining clamp screw holes somewhere?.
I have this photo of an earlier car showing some of this wiring in conduit.
Would members be able to add a relevant image of their wiring.
Regards, Graham

I haven’t actually been aware of flexible steel conduits being used in the '38/39 cars.
I think your 1940 car is generally more like a MkIV than it is to the earlier cars. In the MkIV the wiring loom to the rear is largely fed through the inside of the near side chassis rail whereas in the '38/39 cars it runs externally and secured with P clips. This looked terribly vulnerable to me but I’m pretty sure it was not in conduit.

Here is a couple of frames from video that I took of the very original 1939 Swiss car that was unrestored at the time.


Also another unrestored car.


My early 38 has lots of that flexible steel conduit.
I’ll get pix tomorrow.

Left front, large conduit supplying the headlamp and sidelamp, small conduit supplying the left fog lamp and left horn. P-clip on the chassis near the front.

Right front, small rusty conduit supplying headlamp and sidelamp, which I imagine should pass through the wing support bracket, larger newer conduit supplying right fog lamp and right horn. P-clip on the chassis near the front same as the left side.

Left rear, large conduit possibly supplying rear light module in spare tire door, small conduit supplying lamp in tool tray, but they were disconnected when the car came to me so I can’t be sure yet.

My experience is that even the single wires under the bonnet { electric choke , perol pump[s], coil, etc have single wire flex conduits.
I was told the original source for this small conduit was parachute ripcord flex conduits. Whatever, it’s a bit hard to source these days…
I made the small ferrules for the ends of these. Some 1/4"brass tube in the lathe. I stuck a slightly smaller drill inside to aout 1/8"from the end and used a knurling tool to roll the end over. Actually a knurling tool that a friend had and lent to me that was smooth with no serrations.
Worked a treat and lastly cleaned up the hole in the end. On can either solder them on to the flex or JBWeld.

Hi Ed,

Have you seen this on more than one pre-war saloon? In particular have you ever seen it (where it really matters) covering the loom that runs down the under side of the chassis on the outside and only protected by being adjacent to the external welded seem!

Also, have you seen it used in MkIVs (that don’t have the external chassis run.)


OK. Think I have learnt something here.
Only from the Mark IV was the wiring run internally thru the chassis so if mine doesn’t run in the chassis it would have required this flexible steel conduit protection. Correct?
Regards, Graham.

Well the wiring looms that I have seen in
1938/39 cars have run in the inverted L shape formed by the chassis side wall and bottom seam and were unprotected (surprisingly).


The 1940 saloon we did didn’t have the wiring loom to the rear in conduits, just wiring clips along the outside of the chassis using the same holes as the petrol line clips
The wiring at the front was in conduits. To horns etc, but like earlier SSs, the loom across the front of the engine was in a conduit, behind the chassis X member just in front of the engine.
Although superficially like a Mk IV , when you went into it . not a lot was the same.

Here is my '38 wiring. Pairs of P-clips holding the wiring harness and petrol pipe.

I counted 10 of these P-clip pairs along the left hand chassis rail, and there might be one missing at the back where the rail has been replaced.

Looks like the steel conduit was only used where the wiring would be exposed to a lot of road dirt and stone damage. But it is not on the single wires to the front wing side lamps.

By contrast, my Mark V wiring has flexible plastic sleeves in these places.

Your chassis wiring looks to me to be totally original, and totally crazy. It would seem that they put metal conduits where people could see them and not where there was real danger of damage.

When many years ago I was installing my loom I discovered the crazy routing along the chassis and couldn’t believe how vulnerable it was so I ran mine through the chassis rail instead.


It would be extremely hard to guess all this stuff.
Thanks for all the time and effort in your replies and the excellent photos.
Most appreciated. Regards, Graham.

Would anyone have a wiring diagram showing, for the first time, the RJF91 control box.
Possibly the 45-46 cars.
Interested to also see which the first drawing is to show an electric clock.
Regards, Graham

The RJF91 L1 model JUNCTION BOX, Lucas Part No 337909 was fitted to 1938 3-1/2 litre Saloon, DHC and SS100 – according to my period Lucas catalogues

The 1940 saloon we did had the 8 day clock. I presume electric then came in postwar.
Originally as an everyday car, the8 day were more reliable. But you needed to be using the car regularly to wind it. At least, with no attention at al the electric was accurate twice a day.

Sorry. Forgot to mention I was referring to the 2 1/2 saloon. Messed it up again.
RJF50 L3 337709 later replaced with RJF91 L12 37046A.
Would like to see a wiring diagram for the 45-46 2 1/2 if available.
Regards, Graham

Stop press.
Just in
Scan_20181002.pdf (170.5 KB)

I think one might find that the difference was only in the fuses Possibly to do with the change to an electric clock

This appears to have happened[ the clock] at chassis number 90001-90068 and S61001 and subs.
Although at some stage the cover over the reg points was changed from brass to bakelite. The brass havin two tiny holes for a wire and lead seal… Apparetly to stop unqualified owner fiddling where they should’t. This seems to have been solved by the intervening WW2.