Dashboard wiring loom - should I?

[Moeregaard]

Definitely replace the loom and fuse blocks while you're in there. I did this on my first FHC, back in 1991 (when it was "only" a 27-year-old car), and never regretted it. Your original loom may appear to be in good shape, but if you look closely you'll find areas where the insulation has become brittle, or has become damaged through chafing. Replacement just eliminates the wiring itself as a cause of electrical issues. It's not a difficult job if you take photos beforehand and work methodically during installation. Before reconnecting the battery, buzz everything out with a continuity tester to ensure that nothing is shorting to ground.

[64etype]

If you want a robust electrical system for the long term you might overlay the "Bob Skelly" redesign over the original system. It adds multiple relays and new fuse panels (in most cases superseding the originals). My expansion of his design philosophy is depicted in the photo below. At the top of the "stack" are two 40 amp fuses...one for switched (by the key), and one for un-switched (hot) circuits. Multiple relays are on the second tier, a large fuse panel is at the bottom. A second, smaller panel resides behind the false back of the glove box. The original wiring looms are unmodified. Some wires were re-purposed. A number of new load carrying wires were added. Panel switches (including the ignition switch) now control relays rather than carry component loads. A plastic loom cover protects the new fabric enclosed loom from SNG. It's all completely reversible.

[PeterCrespin]

Do the fuse blocks (clean & retension), the switch if sloppy and especially if it gets warm, and clean conntacts all round. I’d exercise the rocker switches after spraying a bit of contact cleaner through a wand from behind (which also redistributes the grease inside). Having done that, the chances are your historic Browns Lane harness will last 20 years and if it doesn’t, you’ve already done everything but the loom itself. The other hsrnesses suffer much more.