FH - thinking about wiring

 This is the wiring diagram we will use for the FH. It comes from Pitman - Waller doesn't show a diagram for Ariel's of this period for some reason.

We’ll need some additions to that harness of course:

• An earth cable from the rear light to a central earth point, including a connector to allow us to remove the rear part of the mudguard 
• An earth cable from the magneto to the cutout button, including a connector to allow the cutout button to be removed
• An earth cable for the headlamp
• Wires for the indicators
• A fuse

We will also rethink the 5 way connector block - it makes no sense to take the headlamp cables through it other than the main feed from the lighting switch. It’s the interface between the main harness and the instrument panel, so we can run the battery cables through it, the earths and possibly the yellow charging cable. 

Lucas started to adopt a standard approach to vehicle wiring in the 1930s, on the Austin 7. We can see that Ariel (supplied of course by Lucas ) followed this to some extent:

• Black: Anything connected to the chassis earth;
• Brown: Main battery distribution circuits, containing no fuses and no switches;
• Red: Side, tail and instrument lighting; number plate illumination;
• Blue: Headlamps;
• White: An unfused feed, live only with ignition switch on;
• Green: A fused feed, live only when the ignition switch is on;
• Yellow: Circuits involved in or related to battery charging: dynamo, voltage regulator.

Lower level identification could be done by the use of coloured sleeves, as witnessed by the original looms with my 1951 Mk1 Square Four. The standard wasn't formalised until the late 1960's released of BS AU7.

It wasn't until the 1950s that PVC began to appear in wiring looms; hitherto, cables were covered in braided cotton.

This is the original loom from my 1954 BSA Bantam, setting the scene for the FH harness. We’ll do that in PVC.