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Working With Series Electrics

Working With Series Electrics

As owners of older Land Rovers, sooner or later we have to deal with electrical issues, coming face to face with the limitations of the original spec loom. To make things worse, invariably the loom is seldom in the same condition it was in when fitted; grafted patches, spliced in auxiliary wiring and a host of other "modifications" can contribute to the general frustration of trying to find the fault in the middle of all the queer coloured spaghetti...

Armed with a few basic tools, a circuit and a selection of basic crimps, most of the irritating faults can be dealt with easily... A meter, wire cutters, wire strippers and crimping tool to suit your replacement crimps should be essential parts of any tool kit; just twisting the wires together and schlepping insulating tape over the lump isn't gonna cut it, any more than leaving bolts done up finger tight if they're fitted at all...

A basic test meter takes all the guesswork out of assessing where problems are hiding, and can go a long way towards pin-pointing the exact nature of a fault; look for something with a display that reads both Ohms and DC Volts;

Ohms (measurement of resistance) allow you to continuity check a circuit that's disconnected from the battery; the lower the resistance along the length of a piece of wire, the better its general health. High resistances generate volt drop along their length (the wire becomes a heater) robbing power from the desired "load" at the end of the wire.

Volts will indicate the potential present (provided there IS one present) in a circuit; higher numbers (up to 13ish) are good; anything below 12 and you have issues.

The biggest advantage the Series loom has over more modern circuits is its simplicity; there's not a lot of anything in there TO go wrong in the first place, and there's a total absence of anything remotely complicated.

Two types of feed power every circuit in the vehicle, either battery or ignition live; battery live circuits can be energised irrespective of whether the ignition switch is armed; ignition live circuits de-energise with the ignition switched off. The circuit switches have to be rugged enough to handle switching full circuit loads; the near total absence of any circuit protection is a double edged sword; any fault large enough to blow the few fuses that ARE fitted is liable to cause a ton of damage before the fuse overloads. The only advantage of this is, again, simplicity. Once power leaves the switch, the next thing it should "see" is the load; any intermediate connections along the length of the circuit should, to all intents and purposes, be invisible to the circuit.

Typically, corrosion is the bug-bear of any old wiring loom; the near total absence of any ground return lines means that the body work has to fulfil this function, invariably made all the harder through the use of mild steel self tapping screws driven into soft aluminium skin causing a host of bi-metallic issues, without throwing a brass or tinned copper crimp in there for good measure. Over time, these connections corrode, adding resistance to the circuit.

Wires themselves can suffer corrosion too; the multi-core nature of wire means it's perfectly suited to drawing in water through capillary action. Pure copper is pretty resilient stuff, but over time, the impurities present in the water being absorbed will break down the copper, returning it back into its oxide state (black) or reacting to cause copper sulphate crystals (turquoise), neither of which conduct worth a damn. When stripping back an old wire to fit a new crimp to it, anything that isn't bright, shiny and salmon pink is corrosion (unless you're adding tinned copper wire) and needs to be scraped back to good clean metal before you crimp.

One other dead simple mod you can do that makes a hellova difference (double light intensity for instance) is adding PROPER ground wires, running back to either a properly bonded ground point, or better still, back to the battery.

If your loom has degraded to the point where, irrespective of how thorough you've been when re-making connections, you still see significant loss of voltage (volt drop) along the length of a wire, it's time to make a decision. You can either replace the wire and hope that fixes the problem, remove the load from the wire by using the circuit to energise a load switching relay, or replace the entire loom.

Now you're thinkin.... "hang on... relays...??? whazzatt then...???" Remember I said earlier that Series switches need to be tough enough to switch full load? With relays present in the circuit, the switches aren't subjected to a fraction of the pounding they take whenever switching full load. Instead, closing the switch energises the relay coil; a wee electro-magnet built into the relay. When energised, the coil closes the switch part of the circuit sending power to the load. Corrosion basically strips away the efficiency with which a wire can conduct current. Putting more current through a wire than it's physically capable of handling will cause the wire to overheat, increasing its resistance, which in turn will generate even more heat causing even more resistance... you can see where that ends up. By converting the original loom to switch relays rather than full loads, you all but render potential overloads of the tired loom impossible; the loads involved are just too small.

Relays can introduce significant advantages to ease of future maintenance and general safety (provided they've been properly installed). There's tons of relays available, along with proper relay holders too; the ones to select should incorporate additional fuses too, at least one fuse for every relay present. The best combined fuse / relay base modules will have pre-installed links between the fuses and relay switch pins, possibly distribution links between the fuses too which can greatly simplify the wiring you'd need to do.

So how about preserving a replacement loom for better longevity...

The worst fault of the original spec loom is it's built down to a price; Lucar connections make no provision for minimising water ingress into the wire, much less allowing safe disconnection without unduly straining the connections themselves. Invariably, trying to disconnect a Lucar bullet from its connector rips the bullet from the wire... There has to be a better way...

Water ingress can be slowed simply through sealing the gaps between the bullets and the insulation with an effective water block; clear nail varnish followed by liberal applications of petroleum gel are a reliable and cheap way to do this, the gel also doubling as a contact lubricant when you need to disconnect.

More reliability can be had by changing the male bullets for insulated bullet crimps, giving you something other than the wire to tug on when disconnecting. As mentioned previously, they can be sealed with nail varnish and gel. Protection can be farther improved by adding sleeving or adhesive heatshrink over the insulated part of the crimp, running back down the wire insulation. This extra layer serves as a strain relief for the connections, transferring mechanical loads into the length of the wire rather than focusing them into the crimped end.

A far better solution is to lose the Lucar connectors altogether, replacing them with something far better suited, but if you choose this path, you need to take all the requirements into consideration. Ideally, a good connector will keep the connections inside it free from grime and water, properly strain relieved, and be quick to disconnect.

Connections to it should require minimal tooling to facilitate easy / improvised repair that's good enough until something more permanent can be done.

Finding connectors that can handle all those requirements are pretty thin on the ground, but they're out there... just don't ask how expensive they are...
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spoken like a true spark chaser. Which is over my pay grade. Pictures really make it easy! Thanks so much.
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