Wiring Vehicles - Planning Electrical Upgrades

Planning any electrical modifications or upgrades to a vehicle is the most important aspect of any wiring project, it is this stage which ensures the correct type of upgrades are thought out, and the correct materials are sourced. Many off road vehicle drivers or users who drive in hostile conditions will take the opportunity to upgrade the original wiring system to remove the compromised original wiring system, and replace it with a much higher quality system.

Consideration needs to be given to the scope of the work to be done, what is the planned work to entail, how it will be done, and will it mean removing the vehicle from the road to do all the work, or will it be done in stages.

How much can you afford is the next question, in the current climate it may be that the work will be done in phases due to financial constraints, as if most people could afford the work it would be done by a professional as expense is irrelevant.

Work can be broken down into two stages, existing wiring or electrical upgrades and accessory wiring.
Existing upgrades could be a popular headlight upgrade which means replacing poor headlight bulbs with much higher rated bulbs, so thought needs to be given to the existing components, are they up to the task, and if worn, what needs upgrading.
New installations for accessories are not so demanding, time can be taken to install new accessories in stages, and as finances or time constraints allow, wiring looms can be made over time and the accessories sourced as required.

Let’s plan a basic headlight upgrade:

Before we begin we will refer to the first section to calculate all our loads, the normal headlight loads are 55w on main beam and 65w on full beam.

Our formula is watts divided by volts to give us amps.

65 watts divided by 12V = 5.42 amps per headlight on full beam

55 watts divided by 12V= 4.58 amps per headlight on main beam.

We already know that we have one relay fitted to operate the main beam and another to operate full beam, these must have a rating of 2 X 5.42 amps for full beam and 2 X 4.58 amps for main beam for our standard headlights.

If we decide our uprated headlights are to use 80/100w bulbs we use the same formula to calculate our additional loads, these are:

100 divided by 12 = 8.33 amps per headlight on full beam.
80 divided by 12 = 6.7 amps per headlight on main beam.
This means our circuit now needs to deal with 2 X 8.33 amps for the full beam relay, and 2 X 6.7 amps for the main beam relay, and that our existing standard cable will handle 8.75 amps as it is the older standard cable and not the newer thinwall cable. This leaves us with the dilemma of should we upgrade the cables to the headlights, as we know it will be worn and suffering from corrosion, the answer would be yes.

We know our vehicle has the capacity for additional extra loads within the fusebox as a number of optional electrical accessories were available to be fitted to the vehicle, so has some spare capacity and will be fine.

Moving to our fuses we see that the standard headlights are individually fused for both main beam and high beam, so we need to look at upgrading these fuses to cope with the additional current loading, as these would easily blow as the lights are turned on. This is because the lights draw more current as they light up, this is called surge and lasts for no more than a couple of seconds, but this surge will draw more current than the standard fuse rating.

We now have the information we need for our plan, if we find the wires to the headlights and note the correct colours we can refer to our chart for the correct rating which would ideally be thinwall 32/0.20 16.5 amp as it is well in excess of our requirement. All we need to do is find this from our headlamp connecter, identify the predominant and tracer colour and measure it, we now have our cable.
Relays are fine, but could be replaced if there is any issue with them, or left if cost is a factor, and our fuses need upgrading from the original 10 amp rating to a new 15 amp rating. In addition we will need the terminals for our headlight plug, these would be un insulated female blades with a locking tab, and these are available in packs of 10.

We now have everything necessary to perform this task, and the information to price and order the required equipment to properly wire the headlights for a quality headlight bulb upgrade, this is a slightly over engineered upgrade, but one which will last. This ensures we keep the original wiring colours to ensure anyone referring to an original manufacturers wiring chart will know what they are doing in the future, should a problem arise.

Earth problems become a problem on older vehicles, this is because older vehicles wiring deteriorates, and the vehicle body is used to earth many components; as the vehicle becomes older its body deteriorates, and the vehicle is usually earthed at one point. One simple modification is to run an earth loom around the vehicle, this can be used to earth each individual panel and allow a separate earth point on the body, and additional earthing points in the vicinity of potentially problematic items of equipment.
Most battery negative terminals have an earthing braid or cable attached, these are connected to the vehicle body and the engine, and this may be done in two ways, one earth braid or cable directly from the negative terminal to a tapped hole in the vehicles body. From here another earth braid will connect to the engine block.
Other systems connect two separate cables from the battery, one will go to the tapped hole on the vehicle body, the other to the engine block.

Making an earth loom is simple, obtain a cable of the desired earth cable to match the vehicles original earth colour, this is usually black with most vehicles, with a current rating of around 25 amps, in thinwall cable this would be 28/0.30 2mm CSA. Obtain a number of un insulated ring terminals to fit 2mm CSA cable with an appropriate sized hole to fit a bolt through, and one un insulated ring terminal to fit the 2mm CSA cable with a hole suitable for connection to the battery negative terminal.
Crimp the battery terminal to the cable, if you have a soldering iron of a suitable size, solder this connection as well, only use electrical solder as other types corrode the joint over time, and connect to the battery. Run out the cable and attach it to the existing wiring loom, at a pre determined point, break the cable and attach another ring terminal by crimping and soldering, with the remaining cable, crimp and solder another end to this, where the two ring terminals meet, attach to the vehicle body. Unsure the body is clean before bolting the two rings to it, once bolted, paint the cleaned meat thoroughly and leave until it is dry, coat the now painted ring terminals with a liberal coating of petroleum jelly. Continue with the next length of cable and make joints with the vehicle body as required, ensure any electrical components such as lighting units have a ring terminal joint nearby; you now have a substantial earth loom for the vehicle with a direct path to the battery earth terminal.

Should a problem arise with a corroded earth, or a problem with an earth wire on a specific item, all that is needed is to make a new earth terminal from the affected item to a termination point in the new earth loom, ensuring a direct earth path to the battery. Many people often take the opportunity to earth every item of equipment while they are making an earth loom on older vehicles, this is a good preventative measure where older wiring is encountered, particularly on off road vehicles. Such a task is one which can be done in stages and costs very little to do, it often eliminates problems before they arise.

Planning this task is simple, all we need to identify is the quantity of cable required, always order a little more; the number and type of ring connectors we require, and a little paint, and electrical solder to complete a considerably improved earthing loom.

Back to Section 2