and back to bus problems.
Got to see the RML at last and surprise, surprise, it doesn't have a "slipping" reverse. New owner was "told this was the problem"!

When reverse is selected it selects a forward gear. We think 1s. however, all forward gears function normally.
Immediate thought was earth fault and there are a number of suspects as to where that could be. Headlight on N/S wing not working, pull-out plug has been bypassed with direct wires and bulb is 3-pin car type bulb.
N/S saloon lights don't work on both decks and one side of the conductor's switch has been replaced by a push button switch.cab dip switch doesn't come back up and jams down(this is being replaced.

Is there an easy way to establish if there is an earth fault? I heard sometime back that you can tell if there is an earth fault by holding a bulb unit with 2 wires and put one wire on the + battery and touch the body with the other, if it lights there is a fault, or is this rubbish?

I think I know the answer to this but I'll ask anyway - as the bus is set up for automatic gears, IF there isn't an earth fault, would putting in the by-pass wiring on the "Christmas tree" making it manual change make any difference?

We checked the Control panel and gear selector switch, all contacts and terminals in really good condition.

Thanks in advance

My bus number (if any): RTL 960, RM 1585, RMC 1486 and several RTs

The nearside lights on refurbished RML's only operate if the alternator is charging. Check to see if the cab fan works as it is also fed this way. There are two relays fed from the field winding. One at the rear and one at the front. If the charge light doesn't illuminate when the ignition is turned on it will almost certainly be an alternator field issue. I had this fault last week. Luckily I found the field cable had come adrift on the alternator.

Yes, you can use a lamp between the battery terminals and earth to check for earth faults. If the lamp glows there is a fault. Check for both +ve and -ve faults.

If a forward gear coil on the ep valve is to earth (with another opposite pole earth fault on the bus) then it can energise along with the reverse gear when selected. Had this on DM's in the past.

Oh and no, the old style shorting plug doesn't work with the new style gear controls. You need a different plug which shorts the lead that connects to the gear control panel.

I suspect a number of faults exist.

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

Brian

Assuming the wiring is correct on the bus the test lamp should not light. If it does then it indicates an earth fault through the body which has either a - connection to it made by someone who does not understand insulated return or an insulation break in a wiring circuit.

Not sure about the gear change problem but could be a fault in the 551 unit if it has one. Wiring it for permanent semi auto via the ' tree ' will bypass the 551 unit, however the speedometer will not work unless the feed is retained to the 551 unit to receive the transducer signal.

David/ Ed
Thank you both very much for those helpful replies I'll pass them on.

David can you explain what you mean by "There are two relays fed from the field winding" please?
I've found out that only the N/S saloon lights work and this is when the engine is off, is it possible on this bus that O/S have cut out due to alternator not charging?

My bus number (if any): RTL 960, RM 1585, RMC 1486 and several RTs

There are two small connections on the alternator which are connected across the battery switch field contact. When you isolate the battery this breaks the field winding first to stop open circuit charging which will damage the alternator. The alternator connections are marked A and WL. The +ve from the run position of the starter switch feeds the warning light. The other side of the lamp connects to the WL on the alternator. When the bus is latched in the 24v runs through the lamp and uses the alternator field as a -ve and the lamp glows. When the alternator charges the opposing 24v extinguishes the lamp. This 24v also energises two relays. One behind the panel next to the drivers seat where the old regulator was sited and another above the conductors light switches. The cab relay switches on the feed for the cab fan, the rear feeds half the lights up and down. My bus switches the nearside saloon perhaps others differ.

Thanks again David

My bus number (if any): RTL 960, RM 1585, RMC 1486 and several RTs

For the lighting issue you may find a small inline spade type fuse underneath the O/S rearmost bench seat cushion has blown or corroded. Visually it may appear fine but check by changing.

My bus number (if any): RM531

Good advice all along from above, saves me a lot of typing. I'm sure my RML lights are n/s on all the time, o/s only when charging. The blade fuse under the rear long seat usually burns out the fuse holder, I've had to replace mine twice in 8 years!

The 551 panels are getting unreliable, I've replaced 4 in the last 18 months, usually dry joints and defective NATO connectors.

do the mod on the Christmas tree to see if that solves the problem, if it does, get the panel checked out at PSV electrical, Hoddesdon.

My bus number (if any): RML2532

Thanks Steve/Roy.
Bypassing the Christmas tree to enable semi auto operation as a "cure" was suggested to me by someone who'd read about it, but I can't see how would that have any effect on reverse not working given that reverse is a "selected" gear.

It now transpires the previous owner could get reverse but it was slipping. The selection of reverse getting a forward gear is a new phenomenon! Also the switch under the stairs for the O/S saloon lights has been replaced with a push button switch.

We are going to start with the earth test, look at the bodged N/S headlight connector, light switch and the dip switch which appears stuck. We'll also look at the fuse under the bench seat and take it from there.

Thanks again.

My bus number (if any): RTL 960, RM 1585, RMC 1486 and several RTs

Following on from the information David has given regarding the relay for the heater fan motor, this was necessary to ensure that drivers did not drain the batteries by leaving the heater fan running after engine switch off.

That's interesting Roy, I have always had my reservations about these so called military spec units. I have always understood that many electronic components degrade with age, and if these units are beginning to fail on a fairly regular basis then perhaps more buses will be converted to permanent semi auto mode. From my own experience I preferred manual gear selection, however that is only from an enjoyment perspective and not if I was driving professionally.

Good decision brian. Exactly the right thing to do. Earth fault first followed by the other known faults. Not sure about the fuse. Not shown on the refurb drawing. If it is there it would be taking the whole lighting load. Cummins drawing shows nearside lights switch off. The interior advert and cab heater was also fed this way on original RM buses.

Roy. You surprise me. That is a unit changers methodology. Why not change the gearbox first and be done with it! Still, glad I could save you time typing.

Brian.
I will say that it can be a long and daunting task chasing earth faults. For a start it could be accumulative. Several highish resistance faults that become an overall low resistance fault. Watch the lamp as it may dim slightly when a circuit or component is disconnected and would indicate that circuit to be contributory but not the main or only problem. Steve griffin may remember better than me likely places to look for

The Christmas tree bypass would prove

a) selection from the gear selector to the gearbox is correct; you should be able to get all forward gears individually; you should get reverse when reverse is selected;

b) if you get more than one gear selected, the fault is in the wiring from the selector to the gearbox, usually the 7 core cable chaffed where it enters the EP block;

c) if that isn't the problem, check you are getting air to reverse when reverse is selected;

d) if none of those, the problem is in the control box;

e) if there's still no reverse movement, reverse gear brake band may have been worn out. This is very unlikely to happen in normal service as reverse is rarely used and could indicate two gear selection, so back to the earth fault scenario. You will need to gear the gearbox rebuilt.

I usually have one in stock ready to go on an exchange basis as other suppliers may have.

edited to add if reverse gear doesn't work the bus will naturally creep forward due to the natural movement of the gear train even in neutral.

My bus number (if any): RML2532

Hi Ed. hadn't noticed your post. Military spec connectors are about as good as you can get but at extra low voltages gold contacts should be used. The 24v higher current circuits will generally be fine but signal voltages will suffer from corrosion with tinned copper connections. It doesn't help that our buses don't see the use they once had often sitting in damp conditions for long periods with no maintenance. Relays can also suffer at low voltage and current use.

Normally perhaps but in this case not correct and for someone that has regularly stated earth faults to beg such a big problem AND how the switching arrangement changes from negative to positive when the panel is bypassed I'm amazed you cannot see it could result in everything working correctly only for the same problem to return after paying for a new panel.
This is why skilled electricians were employed by LT rather than allowing BM's or bus drivers to carry out electrical work.

I should have said earlier, It's got an IVECO engine, don't know if that changes anything re the saloon lighting.

We checked the gear selector switch in front of the steering wheel and it's in really good condition and the selector functions properly, The Control Panel above the driver's head is also in excellent condition with no loose connections and terminals.

They are keen to try this bypass to see if that will cure it, but I could not see how changing from automatic mode to semi would help, the reverse still having to be manually selected in wither mode. But, I'm only a bodymaker :-)

My bus number (if any): RTL 960, RM 1585, RMC 1486 and several RTs

I've not seen an Iveco or Scania drawing but I'd be surprised if it's different. More likely it's been swapped over or the drawing not followed properly.
You could try the bypass first and it may give you a fix but don't assume it's the panel if it does work as the switching on the negative becomes switching of the positive when you use a shorting plug. If you simply short out the terminals it is possible to continue with negative switching by changing the selector common to negative and the ep valve common to positive. That would at least keep the flow the same and keep the fault in place if it is an earth fault causing it.
Permanent bypass will stop the standard speedo working unless you keep some of the panel in circuit. If you have a separate tacho it shouldn't be a problem.

The bypass wiring will only prove whether or not the gearbox works properly and that you've got feeds from the selector to the ep block. If you find reverse works ok, then it is unlikely the fault isn't in the box and you have to delve more into the wiring.

My bus number (if any): RML2532