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Re: Isolation Switch Puzzle ???

Oddly enough our bus has a Recon AEC 760 engine converted for a Routemaster.

Thank you for your reply. I'm just wondering what this cutoff switch is for?


It appears to interrupt the + line from the batteries

You may have seen I've had some power problems and I'm trouble shooting for possible drains.

If this switch stays on and does not cut off when turned off, could it be the source of a voltage drain?

Also I should ask if there are known power drain areas??

My bus number (if any): RCL2259

Re: Isolation Switch Puzzle ???

The battery isolation switch does exactly that. It isolates the batteries. You cannot start the bus with it switched on as the starter will not work. It helps prevent shorts causes fires.

As Matt had said above, once started the engine needs no electricity to continue to run, which is why you have a fuel cut off switch to stop the engine.

My bus number (if any): RTL 960, RM 1585, RML 2667 and several RTs

Re: Isolation Switch Puzzle ???

Try checking for negative to body and positive to body. Lots of people these days put a fag lighter socket in the charge their phone, and invariably connect negative to the body, which should be neutral. also check the wiper motor. If it's mounted on the front screen they're a source of negative earth. simply pit light bulb in a holder with a couple of bits of wire. tough one wire on the body, the other on negative. If the bulb lights you have positive to body. Try with wire to body and wire to positive, if the bulb lights you have negative to body.

Tacho fitted? That can be a drain on the battery if you don't set the switch to REST when you leave the bus.

My bus number (if any): RML2532

Re: Isolation Switch Puzzle ???


Is this switch actually a battery isolator ?

The RCLs were fitted with extra equipment when on sightseeing use and your bus has been used for other uses since service in London, so is this just a switch for some ancillary equipment ?

Just a thought.

My bus number (if any): RM1368

Re: Isolation Switch Puzzle ???

Andrew Morgan

Is this switch actually a battery isolator ?

The RCLs were fitted with extra equipment when on sightseeing use and your bus has been used for other uses since service in London, so is this just a switch for some ancillary equipment ?

Just a thought.
Have tried negative to earth, and positive to earth, and there appears to be no drain. It appears whatever problem I had has solved itself as close day to day checks have revealed no drop now. And Andrew, how have you been? I followed the wires from the switch and they do go to isolate the batteries.

I think when considering the size of this engine, I need to keep a close eye on things. Regular batteries will simply not turn it over, even brand new ones.

For the record, the 142Ah Exide batteries are staring the bus right away, if it had a key, I'd say it hardly has a chance to turn before it starts, and the alternator is pumping out 28.0 volts

I'd say there may I been a short which I inadvertantly corrected while doing the tests. Thanks to everyone here for your help.

My bus number (if any): RCL2259

Re: Isolation Switch Puzzle ???

Sometimes a build of film on the battery terminals or clamps even when tight cause loss of a good connection and simply by disturbing and reconnecting has the effect of clearing it away and making good again ?

My bus number (if any): RML 2747