Hi all,
As I'm in the process of tidying up RML2391's cab I decided to have a look under a few covers !
The first pic shows the connections in the box next to the cab seat . For my records can you identify what's what on the connectors etc ? Also , there's a 5 amp blade fuse does anyone know what its for ? (RML2391 is a cummins refurb)


The next two photos show the wiring in the box next to the handbrake lever , can anyone confirm what they were for as they are all disconnected or snipped ! I'm assuming they are radio related etc ? I'm planning to carefully remove these cables to tidy it up a bit can anyone advise if any of these are likely to be still live and where they dissapear to when they go out of the cab through the ceiling. Lastly anyone got any clue as to what the wire is that goes off through the cab floor , again it has a modern connector on it , can it be removed ?



Many Thanks
Mark 2391

Apologies for anon posting !

Mark 2391

Hi Mark

Your last picture is of the original radio system (from the 70's?) PTT button (Press To Talk) which enabled the driver to transmit whilst driving (early hands free!!!!!) since the left leg had nothing else to do.

Mark

Mark

Firstly be careful with the wires in the box next to the handbrake, as mentioned they were for the radio equipment. There is the distinct possibility 2 of the wires may still be live, so either check with a multimeter or carefully trace the wires. The terminations for the live wires will be in the Switch & Fuse Panel Cab Header above and to the left of the driver.
The connections in the box by the door carry battery + & - power supplies from the batteries and isolator switch. These connections are the main battery feeds for both the Switch & Fuse Panel Cab Header and the Facia Switchboard down to the right of the driver. From these 2 locations most of the essential wiring circuits of the bus originate, with the thermal type circuit breakers protecting certain of these circuits. The relays in the photo are as follows, the start relay when energised from the ignition start and run position will operate the starter motor. The start fuel relay is connected to the fuel solenoid, with control from the ignition switch as well, thus turning the engine off when required. These 2 relays are operated from the ignition switch via the start inhibit relay, which will prevent starting of the engine if the bus is in gear. The interlock for this is located in the 551 gear control panel. The smaller of the 3 relays is the Alternator Field Relay, which is energised from the ignition when switched on, this is also the ignition warning light circuit which is connected via this relay to the battery isolator switch. When the AF relay is energised it provides power for the heater motor in the cab, thus preventing the battery being run down if the driver inadvertantly left the blower on after engine switch off. The ignition warning light circuit also controls the n/side upper&lower saloon lighting relay in the Saloon Lighting Switchboard on the platform, this is why these lights will only operate when the ignition is switched on.
The 5 amp fuse protects the circuit from the ignition switch to the engine run solenoid, when the ignition is switched on.
Going back to the redundant wiring, you may find live wires leading from the cab behind the 551 unit and Bell&Buzzer board going towards the upper saloon. Be careful and don't expect the live wires to always be coloured red as black may have been used for battery + in some instances.

Ed

Thanks Mark and Ed ,
Will tread carefully when removing/sorting out wiring ! One at a time I think !

Mark 2391

Mark ,

Seeing the responses to your enquiries is the simplest to answer as regards the redundant wires on the floor..

I have removed the lot from 2708 and as they are both 'AR' buses the wiring is so easy to remove its worrying ....

ISOLATOR OFF !!!!

1] remove all 'cover' panels behind and to left of drivers head -- 2BA MACHINE SCREWS ... NOTHING MORE JUST THE 3 PANELS

2] remove any plastic covers from the ducting on engine side firewall, once wires removed drill out rivet heads and remove conduits

3] take each wire in turn and gently work it back via all routes until you find the fixing position -- carefully remove from fixing and retighten every screw fixing BUT DON'T OVER TIGHTEN ------- DURING THIS PROCESS you'll find the wires generally go upwards via black pipe ++ black flexible conduit found fixed to left side rear corner of cab .

4] as you remove each wire throw out of cab as rubbish

5] when you get to some thinner wires NOT loose in bottom area conduit BUT CONNECTED INTO THE 551A via its loom DO NOT CUT THEM AND DISGARD , THEY ARE ALL CONNECTED INTO THIS 551A unit for use other than what we need them for. These wires ALL have potential to be live !!!!! so proper dead end termination is a must for safety then they can be safely 'tied' back onto the wiring for the 551A as I've done with small cable ties.

6] remove the GREY !! MULTICORE which goes behind the BELL BOARD along above the DRIVERS DOOR TOP EDGE in box section [not in actual door] --- former radio programmeable unit connection wires all dead .

7] remove ORANGE MULTICORE WIRE -- connections to the 'vehicle location equipmemt' , goes across the overhanging bulkhead above the flap above engine bonnet --- you might find long lengths here OR not as the case maybe -- all dead

8] NOTE EACH wire connection as you go thats been cut as you won't need it again BUT do make a note of which terminal blocks used for these connections that can have 24 volt feeds to them -- can be useful later -- ++++ note the wired earth returns terminations ..

9] ALL wires not needed and found cut can be removed without worry , once done so can the conduits be removed if wanted to as they are unsightly , the cab will look much cleaner/neater and tidier after this effort + it will feel bigger as well .

10] as these are EX 'AR' buses the finished result will be amazingly simple unlike some I've seen . The wiring was altered AFTER REFURB when the ENGINE STOP RELAY was taken out & stop wiring was taken OFF THE START SWITCH due to the STOP relays burning out and the actual 'engine stop' was replaced VIA A MECHANICAL PULL 'T' bar fitted in firewall beside the heater piped water gate control valve.


TOP TIP FOR ALL SUCH CAB WIRING ......... WHEN REMOVING THE STARTER SWITCH PANEL [ as in point 1 ] MAKE VERY SURE YOU HAVE A MEANS OF SUPPORTING IT BECAUSE THE STARTER SWITCH , water low light / ignition light and starter bomb socket wires ARE ALL CONNECTED TO THEIR respective UNITS FIXED INTO THIS PANEL - you really don't need them to break OR COME OFF accidentally ESPECIALLY 'ED R' IF ITS AN EX CAMBERWELL or NEW CROSS MACHINE ... I saw the 'rewiring' on RML 2402 [I think it was] EX ROUTE 11 that is a 'doner' bus, last year and it was worrying to say the least.

Failing ALL of this help Mark , call me and I'll do it for you FOR FREE and the pleasure ... time of job about 2 hours with care

Thanks Alan, very sensible advice and I am sorry I forgot to mention the obvious point of turning the isolator switch off before removing any redundant wiring.
The standard of wiring on 2335 was very poor in places and work is in hand to make the whole system safer. With regard to the starter switch panel it is essential to provide proper support for it at all times, otherwise as you say the wires may come adrift from the various switches etc.
With the 'bomb plug' circuit is there a relay connected to it, and if so what type is it, I am just curious, I do not have the 'bomb'circuit as you know.

Ed

Thanks again chaps for the advice.
Not got round to removing the higher panels yet as the work is concentrating on the lower cab areas . Will post progress with wiring as it happens , also will post a few more photos of whats behind the higher panels for everyones reference.
Just to add the cab does look tidier without the box next to the handbrake and the pastic conduits out of the way !

Thanks

Mark 2391

Hi Ed,

My pleasure to help as always.

The 'bomb' wiring is 3 wires , red / black / green, fairly stiff cored wire and goes thro' a gap along with other wires behind the centre angled panel to which the outer panels are secured with the 2 BA hex head machine screws. It then goes behind the panel - visible when outer is removed - containing the 'DESTINATION & SIDE LIGHT SWITCHES', behind this panel - more 2BA screws - is the 'security panel' containing the 3 small relays I referred to ages ago ++ one more larger relay [inside clear plastic casing], this 4th relay is not known exactly what it does, but I know a man who might have the answer !! Colin is not sure so he tells me. In the wiring to this security panel, once you get there, you'll see a large variety of wiring changes made by the garage electricians depending which company they worked for which is what has taken the 'bomb' out of use , meaning that infact ANYONE WHO CAN READ CAN START THE BUS AND DRIVE OFF ... the biggest reason for 'dewiring' this bomb arrangement was because so many bus drivers at certain garages decided that if they 'lost' the starter key they would conveniently 'loose a rounder' or much of one when telling the engineers they had a NON START because they had lost the key.

If the buses such as at AR/CT/BN and several other garages had and did keep the bomb cct then there are simple means of testing for which relays has failed if the bus will not start if it is just relay failure that is the problem. The 'plug' I have located and mentioned here several weeks ago will isolate one of the possible non start causes and get you home. This plug which isolates the security panel is available elsewhere BUT as I've found the actual plug maker/part number etc etc and will have some to supply at less cost in the near future.

You need to look closely at the security panel as mentioned to see exactly where the BOMB wiring is connected to, I have not bothered, and this will begin to tell you which of the small 'oxo' cube sized relays is activated by use of the key. The s/panel contains a wiring tag strip / thyristors [electronic switching devices]/ resistors, 4 bases for the relays and 2 separated sets of wires, in the case of dewired use of the bomb some wires are cut and taped off..

The security panel is fixed to the bus body with 2 simple self taping screws because it was never there in the first place !!

Beyond that ED I haven't a clue, ho ho ho !!

Alan

Thanks for the comprehensive info, you omitted though the resistance readings for the circuit in use (joking). As you know from our discussions last year about this circuit, nothing remains in 2335 and you had my bomb socket. I was curious because this circuit had been in 2335 at some point. The other reason was that a relay had been left connected to the ignition switch serving no other purpose than to have its coil energised. I thought this relay might have been part of the earlier 'bomb' circuit, and it has now been removed.

Ed

ED ,

Yes I well recalll the discussions etc.. Judging by the combined efforts between us we've pretty well got it all sussed then.

One thing I did omit is this .. in originally wired - pre refurbs RM/Ls etc - it states very clearly in the various 'test' instructions that are available ... 'DO NOT USE A MEGA' , SO question is 'would you use one when working on a refurb'd bus?? I don't know because I've not seen nor come across such instructions for these buses, something to think about perhaps..

Alan

That is interesting, the 'mega' I have is a 250v hand operated one over 50 years old, so I don't think I will use that on the bus. The serious point is I cannot think of a reason not to use a multimeter on any circuits unless for component reasons, say in testing internals of the 551 unit which is the most sophisticated piece of equipment on the bus. The fact a RM has a very basic insulated return wiring system makes it suitable for using a multimeter for testing of circuits in general (volts,current,resistance,continuity).

Hi All

The following may be useful based on what has preceded.

Meggers are usually used for insulation testing, i.e., applying between 1,000V and 5,000 (1KV - 5KV) to test for insulation breakdown, usually in the context of mains wiring or other medium to high voltage areas.

Applying such equipment to a vehicle electrical system designed to run at 24V would, I imagine, not be the smartest thing to do. Remember, a MEGGER with a stated operating voltage of '250V' is designed to TEST wiring that operates at that voltage. The MEGGER tests the wiring by applying a HIGHER voltage. Therefore, MEGGERS in the wrong hands can be very dangerous - a bit like a DIY hand cranked tazer.

One obvious concern would be the effect on the diodes in the generator (alternator). It is for this reason that the alternator should be electrically isolated from the rest of the vehicle when carrying out arc welding. This avoids exposing the alternator to transient voltages (voltage spikes) that will damage the diodes contained therein. When making/breaking electrical circuits switching transients can be very high. In some instances, the arcing associated with them are used to keep wiping switch contacts reliable but, obviously, too much will have a deleterious effect.

A word about electrical safety...

Just as the EHT (Extra High Tension) circuits in early television receivers were (and still are) lethal because the EHT was derived by an overwinding on the mains transformer (with no limit on the current), so the output of a hand cranked MEGGER can be very dangerous. Remember, it is not the voltage that is dangerous but the CURRENT.

So-called 'static' electricity (e.g., the sparks generated when rubbing a party baloon on one's clothing) is not dangerous even though it is at many thousands of volts because the current is miniscule. But even 24V in a commercial vehicle system can be dangerous if the high resistance of the human skin is overcome because of a cut. Scenario: Enthusiastic bus owner lying with rolled up shirt sleeves with sweaty arms against grounded bare metal touches live conductor with fingers of other hand that have sustained a cut and are covered in a sweat/blood mix. A left hand to right arm shock in such a situation at 24V could stop the heart. The voltages sensed by a Pacemaker for the human heart are about 2mV - 5mv (2 - 5 millivolts) or two to five thousandths of a volt. This is all VERY LOW VOLTAGE stuff. In other words, it is the voltage drop across the heart that can do the damage. And remembering that it is the CURRENT that is the villain of the piece and the batteries in our buses are designed to provide lots of that we have a potentially dangerous situation. All you have to do is get the right current through the heart and the right voltage drop across the heart and bingo!

Is it really dangerous? I wouldn't like to try it!!!

High voltage electrical shocks are often not as dangerous as low voltage shocks because the skin burns and its increased resistance in that state rapidly limits the current. With a low voltage shock, on the other hand, there is no burning...

If one really has to work on 'live' equipment follow the basic rule of keeping LEFT hand behind back.

John

John

The reference to 'mega' I made was somewhat tongue in cheek. Meggers were used for various types of testing in AC circuits, one use we put them to was verifying the polarity when terminating MICC cables (mineral insulated copper covered).
You are obviously vastly knowledgeable about electrical systems, why not become our expert on such matters, single handedly even.

Ed

Hi Ed

It is very kind of you to offer but my experience is over 30 years old and very, very fuzzy. There is no substitute for up to date and relevant hands on knowledge, experience and, more importantly, training. Dutch joke- Question: What's black and charred and hangs from the ceiling? Answer: A Belgian electrician.

Cheers!

John