Firestarter
IT is a while since I last had a 24 volt FFR (Fitted For Radio) Series vehicle come into the workshop. MOD portable radio equipment has run off a 24 volt supply for decades and there are two approaches to fitting this to a Land Rover which normally has standard 12 volt vehicle electrics. The first is to separate the radio electrics from the rest of the vehicle, which is what Land Rover did with the very large number of radio-equipped Ninetys and One Tens supplied to the Ministry of Defence between 1985 and 1995. These vehicles have a large 24 volt generator bolted to the top of the timing case, and a standard 12 volt alternator to power the vehicle electrics. The FFR vehicles were supplied with an oil cooler, oil temperature gauge and hand throttle, but are otherwise mechanically identical to the GS (General Service) vehicles, and the 24 volt generator and wiring can be stripped out without consequences. The Wolf Defenders (1995 onwards) have 24 volt vehicle electrics for compatibility with the rest of the Army’s vehicle fleet (jump-starting tanks, perhaps?), but the radio system is again a standalone installation with its own generator and batteries.
Series vehicles are a different kettle of fish. The FFR vehicles use a single large generator to power the vehicle electrics and charge the radio batteries. The two systems are thoroughly integrated, with the voltage regulator contained in a mysterious metal box between the seats. All the harnesses are screened with braided metal conduit, the system was revised several times during production, and fault-finding can be tricky to say the least. Fortunately there is quite a lot of information on the Internet about these systems, but an FFR Series IIA or III can throw up some challenges, and parts availability is patchy.
The Series III 109 hard top which came into the Norfolk Garage a few weeks ago certainly had some electrical issues. Various lights out, no fuel gauge, indicator tell-tale glowing constantly, no charge warning or oil pressure light, no panel lights and, puzzlingly, an engine which continued to run when the ignition was switched off and could only be stopped by stalling it against the brakes. Lifting the bonnet I could see that someone had been there before me, with numerous non-original wires draped across the engine bay along with relays and fuse holders whose purpose was obscure.
Faced with this kind of spaghetti wiring there is only one sensible approach. Rip out absolutely everything non-standard and then see what still works. About the first thing I found was a live unfused heavy duty wire from one of the battery terminals which had been routed under the edge of the steel battery cover. This had cut through the insulation, leaving the vehicle only a coat of paint away from a wiring fire. I followed the wire forwards, duct taped along the transmission tunnel and up the bulkhead, through the instrument panel area to a relay cable-tied to the steering box. The output from the relay fed the ignition coil, and I now understood why the engine kept running with the ignition off.
Although most of the electrics on a Series FFR (lights, wipers, heater and so on) are 24 volt, the ignition system uses a 12 volt coil, with the ignition leads, coil and distributor all electrically screened. The system is fed from a ventilated metal box attached to the top of the rocker cover, which contains two large resistors to drop the coil supply voltage from 24 volts to 12. On this vehicle the screened ignition system had been replaced with a conventional one and the resistor box was missing. To replace it a 12 volt supply had been tapped from the connecting cable between the two vehicle batteries (12 volt batteries wired in series) and then fed through a relay which should have been energised from one of the ignition switched vehicle circuits. Somehow the installer had managed to feed the relay off the generator instead, so that with the engine running, when the ignition was switched off the generator output would keep the relay contacts closed until the engine was stalled, at which point they would open. I’m still not sure exactly how they managed this rather neat trick as I just pulled out all the substandard wiring without paying much attention to how it was connected.
I could have replaced the system with a slightly better engineered and less flammable version, but instead I decided to try using a 24v to 12v converter. These are readily obtainable: truckers use them to power stereo systems, portable fridges and the like. The one I chose was rated 15 amps which should be plenty, and had a common earth for the 24v and 12v circuits. That is important as the ignition system earths through the engine block and cannot readily be given its own separate earth. It fitted neatly on the bulkhead but I am not convinced it is the best system I could have chosen. It has protection circuitry which ramps up the voltage slowly (over five seconds or so) when energised and cuts the power if the input voltage drops below 18 volts. The problem is that if the batteries are a bit tired, the initial cranking voltage when the starter is engaged can drop below the threshold, and then the engine has to spin over on the starter for about five seconds before it fires up. I can foresee this causing problems in cold weather, so I might look at replacing the converter with another one. I tried a wire wound 50 watt resistor but it got very hot very quickly, and really high wattage resistors are hard to find.
The rest of the electrical problems were just a case of rectifying “repairs” which had been done to the same standard as the ignition feed circuit. The panel light harness and switch were missing: the bulb holder for the oil pressure light had been fitted to one of the panel light apertures, which meant that the speedometer was illuminated for a couple of seconds after startup. If your speedometer lights up, stop immediately to avoid damaging your engine. The glowing indicator tell-tale was simply explained: the standard bulb had been replaced with an LED lamp. I have come across this a couple of times now with indicator and charge warning lights, these should not be fitted with LED bulbs. Charge warning lights in particular are bidirectional and need current to be able to flow either way through the bulb. LEDS are light emitting diodes and the whole point of diodes is that they only allow current to flow one way. Being able to make them glow with minimal current was originally just a useful side effect. On this vehicle the charge warning bulb had been replaced with an LED – sure enough, refitting the standard bulb fixed the problem.
The fuel system still had the original twin underseat tanks with changeover switches. These use plunger switches on the changeover tap to switch the fuel gauge between tanks and can get very unreliable in old age. To my surprise the plungers were fine on this one, but the sender unit on the right hand tank was dead, and the entire wiring system had been bypassed with a direct wire from the gauge to the left-hand (empty) tank. Removing the headlights revealed another often seen bodge: the bulb connectors had been cut off and replaced with uninsulated spade terminals, connected to the bulbs in a random pattern and with the ability to short against each other as an added bonus. One of the headlights had a halogen bulb, the other tungsten. The backing bowls had long ago lost any facility to adjust the headlight aim, so I binned them.
This kind of work is very time-consuming, which is probably why I see so many older Land Rovers with dangerously bodged electrical systems. Returning this vehicle to something approaching factory standard electrics took an entire day, but at least the owner can now venture out after dark with confidence.