I have an intermittent electrical fault on my RM which is very puzzling. On a number of occasions when in automatic gear change mode, the change from 2nd to 3rd and from 3rd to 4th is slightly premature i.e. occurs about 3mph before it’s supposed to. This is annoying as the vehicle is slow to pick up speed. At the same time the horn doesn’t work! The way that I can restore to normal operation is to switch the side/tail lights on and off. As soon as I do this then the horn works and the gear change is effective at the correct speed i.e about 14mph from 2nd to 3rd and 19mph from 3rd to 4th!
This fault first occurred a few years ago and then seemed to rectify itself. However, it’s recently started up again and when travelling to and from Brooklands yesterday, I had to switch on and off the side lights on a number of occasions to return to normal.
Would be interested if anyone has either experienced this or could shed any light on the problem.

My bus number (if any): RM1699, Eastbourne Regent V KHC369, and Regent III AHC442

I know nothing about electrics and thus cannot suggest a reason or cure but many years ago when taking an RM (I think it was 1871) from the Sales Department after a period of inactivity to Stamford Brook for some pre-sale work to be done on it, one unexpected job to attend to was establishing why the bus would drive in auto when the indicators were on even if the gear selector was in neutral!

My bus number (if any): RM967 (Driver/Restoration consultant)

Many thanks Graham, that's good advice. I tend not to use the auto mode as I prefer the manual over-ride, so the loss of the horn is probably the more serious issue!

My bus number (if any): RM1699, Eastbourne Regent V KHC369, and Regent III AHC442

Could be an intermittent earth problem Steve. Get a test bulb set up and put it on the + side of the battery and touch the other wire on the body. RMs don't change up at "full revs" nothing like it! You could check the connections all around the SSG and on the Christmas tree, perhaps David Colin might be able to suggest more!

My bus number (if any): RTL 960, RM 1585, RMC 1485 and several RTs

You will probably find it's water ingress into the cable insulation.

Moisture creeps so it can manifest almost anywhere and cause resistance issues in a wire.
It also causes problems at connection terminals with reactions between the conductive material and the terminal material which sometimes actually insulates rather than conducts the current.

It's a bigger problem on older preserved RMs that were not rewired but on the other hand the wiring on refurbished RMs other than the Marshall ones is appalling.

Laid up and buses just used occasionally get dogged with these issues as they get older.

David Colin is your man for all things electric.

RM1353 achieves near enough full revs changing from 2nd to 3rd in auto Brian, I should know as I drive it often enough and will be behind the wheel again tomorrow taking it for it's pre-MOT check, it's achieves just over half revs from 3rd to 4th.

My bus number (if any): RM967 (Driver/Restoration consultant)

If the original bus is a modified one with cummins etc engine, then the gear panel has been modified to the later type which switches positive from the gear selector to the control panel, and negative to the EP block. I've come across several buses in the last few years with earth faults to body s described above all with gear faults caused by corroded or chafing wires in the EP block area. In effect a positive feed always exists on the "return" side, so a "negative" wire chafing near the EP block will cause a gear to be selected.

This an then back-feed to the control panel and cause all sorts of problems.

Has the OP fitted something like a cigarette lighter socket for a satnav and connected negative to the body? As we've discussed at length on here before, the body MUST be neutral, i.e no positive or negative to the body!

The revs to road speed will depend on the engine/control panel set-up.

My bus number (if any): RML2532

I believe RM 1699 is a Leyland Roy, and your advice is good as always, I don't believe 1699 has had any major rewiring as such.
I didn't think RM can go to full revs in any gear e4ven in manual, something about a fuel pump governor cutting in? But heh what do I know....

My bus number (if any): RTL 960, RM 1585, RMC 1485 and several RTs

The 'original' CAV and SCG electrical set up also has effectively a throttle position sensor bolted to the o/s/f leg of the A frame. This is a delicate bit of kit mounted in an exposed position. While not necessarily seemingly relevant a fault with this will interfere with automatic gear changes. The loom for this will enter the cab in proximity to the lighting circuit. Dave Kreisler has the light box which plugs in to investigate problems with this. He will travel to call outs.

Many thanks for all the advice received so far.

I can confirm that 1699 is an original and unmodified AEC (it was a Leyland when new but has an earlier body B1043).

I've had a couple of earth problems in the past that were sorted. One was traced to a wire feeding a bulb in the upper saloon and the other related to a problem with the EP block. These were resolved long before the current problem but it may well be as suggested that this is a result of another earthing issue.

Just for the record, there's a table of gear change settings on page 140 of the C&C Walker Routemaster Maintenance Manual. This confirms that the speed for the change from 2 to 3 is 12.5 Mph @1370 rpm; and from 3 to 4 it's 18.5 Mph @1335 rpm. Change down from 4 to 3 and from 3 to 2 occurs at 15 and 8.5 Mph respectively.

My bus number (if any): RM1699, Eastbourne Regent V KHC369, and Regent III AHC442

A cable chaffing to metalwork can only cause operation of an electrical item if a pre-existing fault to the body exists otherwise there will be no return path and therefore no current flow. Not an opinion, but physics. Thus if that is the cause there must be a fault somewhere else as well. Easily checked as pointed out by using a lamp between the body and the positive of the battery and then the body to negative as well. If it is a reasonably high resistance it is possible that both a negative AND positive to body fault exists which may not be sufficiently low enough to cause a bang but it will cause battery drainage and could affect circuits in the manner described. A 10 ohm resistive short via the body but ultimately across the battery will cause 2.4A to be draining from them so not too long before you have a non-start.
Individual circuits will need to be isolated to locate the problem. Oh and a lamp may not illuminate if the resistance is quite high but a voltmeter could still show a voltage present. Try both. It will indicate the severity of the fault.

As I have stated before, there is absolutely no electrical reason why a Routemaster cannot have a body return. Again physics, not my opinion. It would, however, need additional heavy cables between the battery post and all separate metallic parts that will be used for the return, but it could be done. It would not have a detrimental effect on any circuit that I can think of except possibly the gear circuit on an RML as there is a change to the original switching method but that could be overcome. Also what is to stop you having a positive earth as it was the original preference with the main reason for changing to negative earth on cars being easier/improved noise suppression which is fairly irrelevant on a Routemaster.

The main problem with any insulated return system, (Routemasters and virtually all UK buildings) is that nothing is 100% insulated. You will always have something tracking to metalwork. That is why we have to have buildings with an earth system as a form of protection and not something that we can use as a return. Now in the UK your neutral is connected to the earth somewhere between the incomer and the substation (depending on the earth system used). That could be replicated on a Routemaster where the negatives remain via insulated cables wired back to the negative terminal of the battery with the mass also connected to the negative but not actually used for return currents. No actual benefit other than guaranteed short circuit protection but nothing wrong with it either.

The above is all fairly irrelevant though because we all want to maintain the originality of the Routemaster and I can avoid a debate with the blinkered.

The issues with the Routemaster wiring is manifold but ultimately simple. Have it fully rewired. The original wiring is long past its use by date. Even the refurbished buses wiring is approaching 25 years old and they really were not done well in the first place. They were by far short of the electrical specification LT insisted I, by then a contractor and supplier of wiring harnesses, followed. They did not even comply with the refurbishment specification. I have seen harder to replace aluminium cables simply left in place and crimped to new copper wires

No one really knew how long PVC would last when it was introduced. In building wiring it began suffering some years ago as the flexibility of the insulation reduces as oils “dry up” leaving cracks and exposed conductors and building wiring by and large is not subjected to anywhere near the temperature changes, dampness, road dirt, salt, humidity and other external influences that go largely unprotected with the often primitive methods of installation found in a bus. Terminals and connections are no longer checked because few, if any, of us will carry out an equivalent to the LT rotas and the fact that there is less wear and tear on the buses with the reduced usage means that component failures are less frequent so terminals of the components are less likely to be remade off fresh. This will lead to poor connections and the faults such as those reported above.

One specific point is the various negative terminal blocks in a Routemaster. They are largely hidden and when a connection is poor, voltages will find their way through the lowest path of resistance. That is what is happening when you see indicators slow or stop when brake lights are illuminated. I suspect this is the case with 1699

Unfortunately, while a building has to be inspected periodically and at least when it changes hands, a vehicle has no such luxury. It is also one of the least important items to those that just want a good looking bus that runs and stops. To some extent it was a necessary evil even to LT. Bright red and able to stop was pretty much their mantra, until, that is, they decided anyone can paint, and another craft was despatched from the garages.

The best time to rewire a Routemaster is when the panels are off so get it done before the bus is restored, and have it done professionally, not by a bus mechanic that happens to own a crimping tool! After all, you wouldn't hire a bus from someone that hasn't been trained, would you?

Dave Kreisler and Malcolm Green are southern based and both ex LT I believe, I am in Chesterfield, will travel countrywide, also Ex LT and contrary to a report above, still have at least fifteen years before HM government will allow me to retire. Unless, of course, Tim has two friends and I have been vainly but wrongly sitting here assuming he means me.

David

My bus number (if any): M1001, RML2276, T806

Some sound advice there from David. I can add to his experience of pvc cables.

I rewired GS67 back in 1980-somthing and that wiring is showing its age with cracking cable insulation. One "nasty" was the wiring to the offside front lamps which for some reason had partly burnt through in one spot.

BEA MLL721 was rewired after it was set fire to in 1972 and though that bus has done very little work since being rebuilt (it needs doing again, but properly this time), the wiring has gone brittle.

BEA MLL738 was rewired during its rebuild back in the 1990s and though that is now back on the road, its wiring is also showing signs of wear without even being used.

I done RFW14 when that was in for rebuild and the wiring there wasn't too bad to be honest, but I didn't want to risk having to rip everything out again when wiring faults showed up. One minor problem there was the fog lamp came on at random, as did the charge light even with the fog lamp turned off. The fault was the fog lamp bulb holder being earthed and another fault in the charge circuit.

RML2532 refurbished back in the days they were being done is a mish-mash of old and new wiring, a mix of "new" wires everywhere, original wiring including the 7-core to the gearbox which caused a failure on the road with paying passengers on, and aluminium cables in places. There's also an intermittant fault with the indicators now working when the bus starts, but they work after a few minutes!

Yes, it has about 10v positive to body and I haven't found the cause yet. It causes the odd non-start but then I have the luxury of a booster pack to stick in the bus! The common fault has been the refurb wiper motors, these have been found to have negative to earth.

There's a local bus electrician round here called Martin Strange who does man-and-van work and Dave at Airlec in Rye who does a limited amount of vehicle wiring at his base in Rye.

My bus number (if any): RML2532

Hi
Can I suggest that you check that the bus is charging ie the control board is pulling in the contact properly and thus giving output.#
From memory we had a problem many years ago with RM1414 when the speedo stopped working (all still as originally built) and I am sure the horn as well.
Thanks to Tim Nicholson visiting around that time it was quickly diagnosed as being control board faulty ie not pulling in (RM1414 still has rectifiers etc on charging circuit)

If bus not charging it will explain lots of the issues esp the bit where you mention running on sidelights.

The relay for the horn is at the front by/under the nose and if older type has been superceeded to SRB210 or something, the modern ones referred to as 6RA also but there are two types as the contacts are lettered differently and if original the relay is on the negative side of the horn blower?

Hope it helps and makes sense and my memory is still reliable!

Mark

My bus number (if any): RM1414 sort of

I have seen this bus from afar and can confirm that it is a very smart looking vehicle. Also IIRC I queried on here some years ago about the purpose of an horizontal plate seen below the body skirt underneath the driver's cab step on this bus. Again IIRC Brian mentioned that this is weather protection for the rectifiers.

To diverse slightly, May's edition of classic and vintage commercials contains an article about the unfortunate loss by fire of a freshly restored vehicle. This was attributed to mice chewing through the wiring of the building within which the vehicle was kept. All was a total loss, but the vehicle was just weeks away from completion and at that moment uninsured. The article contains much valuable advice regarding classic insurance particularly about checking the details and ensuring that everything is declared.

Now to the relevance of the above paragraph. I cannot recommend strongly enough the advice given by David, that professional electrical investigation of this issue would be the best course of action.