Earths 

A word about earths - a bad earth tends to cause an awful lot of intermittent electrical problems. Combining earths eliminates a lot of hassle - bunch all the earths in an area together and attach to a really good chassis earth. Remember that electricity has to go round in a circuit - the wires into a component must be the same size as the ones coming out of it. Since your motor sits on rubber mounts it is most important that the engine to chassis earth is at least as big as the wire going to the starter motor. In some ways two earths is a good idea, in case one breaks - you really don’t want to have your starter motor earthing thru’ your accelerator cable or temperature gauge! Don’t forget that starter motors aren’t fused and are often rated at over 1 kilowatt - that is about 1.3 horsepower - and about 75 Amps...

One word of caution about shared earths though - if the connection to the chassis is not good you will get weird things happening due to partial voltages feeding back up one circuit from another sharing the same earth. Keep that chassis earth clean and bright.

Alternator 

It is a good idea to put a fusible link on the line between the alternator and battery, and another on the feed from the battery to the car electrics. A fusible link is just like a big fuse. Do not fuse the starter motor power lead. A ‘big’ alternator is not a silly idea - if you use a Japanese Import engine it will probably be supplied with quite a hefty alternator at no extra cost to cater for all those electric gadgets that the Japanese consumer demands but we, as true sports car enthusiasts, scorn at. Hell, I don’t even have doors, let alone central locking, power windows or mirrors! So although your car’s total electrical demand is probably considerably less than the car the alternator was designed for it is quite possible you won’t use the car all that regularly (shame on you) so you may as well have it able to fully charge the battery up in record time when you do use it.

Fuses 

 

You can buy fuse boxes in varying sizes that are a much neater solution than having dozens of in-line fuses. Also it means that you can use the same style of fuse throughout your car. Hella make relay mounting blocks that mini relays plug into, so all the wiring is locked tidily in place. The blocks slot together to form banks of relays.

You can buy aftermarket integrated fuse/relay blocks which look quite smart but are fairly expensive. I have never considered using one, however, they are not a silly idea, especially if you will use most of the relays and fuses. I have always taken the following approach, which stems from having the complete EFI wiring loom including the factory fuse/relay box. If you are running an injected engine grab the under bonnet fuse/relay unit which will have all the relays you need for the engine. The one we used in the Fraser catered for the alternator fusible links, fuses and relays for the engine, electric fan, horn, headlights and a few incidental fuses, leaving only six fuses and five relays to go under the dash. Remember to place fuses and relays where they will stay dry and be accessible in case they fail.

The above circuits make up the basic groups that you must fuse so your car won't catch fire if something shorts out. The number of fuses is up to you, but the less you have the more systems you lose when one fuse goes. Not counting engine EFI system I recommend the following fuses:

• Stop (Permanent Power) - stop lights 
• Park (Permanent Power) - tail lights, front park lights, interior lights, number plate light, dash lights (via dimmer if so desired) 
• Hazard/Horn/Indicators (Permanent Power) - obvious, but you need a cunning trick to prevent indicators going when ignition is off - I will explain a little later (although it depends a bit on the hazard switch and flasher unit). 
• Left/Right Headlights (Permanent Power) - Strongly recommend separate fuses left and right. 
• Wash/Wipe (Run) - self explanatory 
• Heater (Run) 
• Gauge (Run) - gauges, warning lights, reverse lights 
• Engine (Run) - ignition system, fuel pump, radiator fan? (could be on separate fuse) 
• Accessory (Accessory) - radio 

The starter motor solenoid circuit is not fused as it is only momentarily in use. That amounts to ten fuses. The next trick is to figure out where to put them. I have my headlight fuses under the bonnet to reduce the length of wire required (which makes things tidier and reduces voltage drop), but it is up to you. You need to place the fuses as close as possible in the circuit to the battery to minimise the length of unfused wire. This depends on the battery location and it may be better to run one big feed from the battery to the dash area that can then split into the power feeds to the various fuses via the ignition switch.