I'm working on some wiring issues on an AEC engined RM at the moment. The problems are intermittent which makes diagnosis more difficult, just as in humans where I have more experience. On one occasion the cab heater fan didn't work, even when the the alternator is charging. Another time the side and tail lights came on dimly without being switched on. There was also an occasion when none of the gears would select despite adequate pressure and voltage. The gears have been hard wired years ago as the control unit has failed and there is no speed sensor on the gearbox. All the problems resolved themselves within minutes but the issue needs to be sorted.

In the box next to the driver's seat the wiring has been modified to incorporate a CAV 440D type voltage regulator. In this box I was surprised that someone has put an in-line fuse between the black (negative) cable from the battery and the body. It was a 3amp blade fuse and it has blown. When charging there is a voltage of 2 volts between the body and negative, 26 volts between body and positive. There is a relay behind the panel near the starting hook which cuts in when the alternator is charging.

I have heard about bizarre electrical manifestations of phantom wiring problems in RMs and I would be very grateful on any advice on how to investigate this. I'm planning to inspect all the wiring and connections I can find, starting with the panels behind and to the left of the driver's head.

Many thanks in advance.

My bus number (if any): RMs 238, 471 and 2213, GS17

It seems like someone who doesn't know what they were doing rewired it!

First to find out if the voltage regulator is compatible with the alternator. Dave at Airlec, Rye, may be the man to answer that for you in the absence of any other suggestions on here.

Quite why there's a fuse between body and battery- is a mystery. Your first list of faults suggest an earth-related problem. What other electrics have been added and earthed to the body? One of the daft ones I found on a bus in Austria was that someone had used a stop/tail twin filament bulb in the tail lamp and had earthed the positive on the bulb holder to the body which caused a lot of problems. apparently you can't get proper light bulbs in Europe.

Have you got a wiring diagram for the bus? I think you'll find basic body wiring is the same across the whole range of buses, with obvious amendments on RMCs and Things with doors and fluorescent lights, otherwise in my experience the differences are in the alternator/charger wiring, and of courtesy refurb buses which still retain the same basics for the lights..

Maybe a thorough rewire is the answer? A couple of years ago I stripped out over 50m of redundant wiring fro the cab area of RML2532! It too needs a thorough re-wire, a lot of the original wiring has mouldy insulation, dry joints where the copper wire has corroded and so on. It's a lot of work but needs doing.

But then you may be lucky and find Someone Who knows More About Wring than I do come up with an easier answer.

I have sent you an E mail Chris.

My bus number (if any): RTL 960, RM 1585, RMC 1458 and several RTs