A new wiring loom part 2 - Fuse holder and Relay Base

Main Aims 

- Improve reliability (existing wiring 79 years young)

- All circuits above negligible current operating via relays

- Minimise the current flowing through old switches in the dashboard

- Upgrade to modern head and spot lamps

- Reinstate Trafficators alongside new indicators

- Addition of hazard switch

- Addition of electric fan to cool engine

- Addition of electric fuel pump

- Provision of electric water pump

- Aux for USB sockets

- Additional interior light

- Upgrade from Dynamo to Alternator

- Replace starter solenoid

- Future proof with spare ways for fuses and relay

- Modern Thin wall copper cabling

- Modern fuse box and relay holder

There are many different fuse boxes available, some are pre-wired and others you build from scratch. I like the look of the MTA range of fuse boxes which are readily available in the UK. They offer a 16 way fuse holder, 4 way automotive relay base and a 7 way micro relay base. They are supplied complete completed with covers and come supplied with all the necessary connectors. They can also be connected together in any combination.

The initial draft required 1 x 16way fuse holder, 1 x 4way automotive relay and 1 x 7 way micro relay. The idea was micro relays for all the load switching and the 7 way base for the LED flasher relays.  Unfortunately the flasher relays are slightly too tall to fit with the lid so I ended up with 2 x 7 way relay base and remote mounting the flasher relays. 

I've used multiple suppliers for the re-wire including:

https://www.3waycomponents.co.uk/ - MTA Fuse Boxes

12 volt planet - Thin Wall Cable in a range of colours

Car Builder Solutions -  Wiring Accessories

https://www.3waycomponents.co.uk/ - MTA Fuse Boxes

Fuse Holder

Using a spreadsheet I listed all the circuits and divided them between the fuses based on power requirement. Some juggling required to observe the max current for 1mm or 2mm cable allowing for volt drop and heating due to bunching the cables together.  

Worth noting the numbers below are rounded up values with everything ON at the same time. In practice having measured the current with the car running the values are far lower. . 

Relays

The number is probably overkill but it does simplify the wiring and means the original switches on the dashboard and within the steering column only need to switch the current necessary to operate the relay coil. This massively reduces the load on the switches and they can happily operate for many more years. 

 
Fusebox prep

1st step was to add the feeds to the fuse holder. These are a combination of 1mm or 2mm wires. They will all need to be terminated at the supply side of the starter solenoid or battery. 

Sunbeam Talbot Ten - Adding 12v feeds to the fuse holder

The fuse holder and the relay terminals all use a similar type of crimp. 

Crimp connection to the fuse holder blade terminal