I don't have a vehicle or wiring diagram to hand. I assume the vehicle does NOT have hazard flashers. With the system isolated and the indicator switch set to its central inoperative position check to see if there is continuity between either bulbholder terminal and the shell of the bulb holder. Repeat the check between the terminals and the bodywork. There should not be continuity.

Establish which is the negative bulbholder terminal, isolate the batteries. Disconnect and insulate the wire to that negative terminal and connect a 2 amp fused wire from that terminal direct to the negative battery terminal. Install 12 volt 21 watt double pole bulbs front and rear. Turn on the master switch and select turn for the relevant side. What happens?

If the system operates normally now then there is a wiring fault somewhere between the negative bulbholder terminal and the negative bus-bar (terminal block).

Any further continuity testing (eg at the indicator switch) should be done with the flasher unit disconnected and the batteries isolated.

Many thanks, will give it a try.

I am back to the bus next week.

Only one question before I get there.

With this 5 volt, or so I was told, front drivers side, I get the remaining 3 flashing OK and a dimmer front driver side.

What I don't understand is why should the front drivers side fail with a 12 volt bulb when it is getting power to the smaller bulb.

My bus number (if any): RCL2259

I doubt it is a 5v lamp. If in series with a 12 it would burn out fairly quickly at 24v. It is supposed to be 2 x 12v in series unless it has been altered. If you have a 12v 21w in the rear and a 12v 5 w in the front the the front will be dimmer than the rear. If it has been altered to 24v in parallel then the same will apply if it is 5w in the front. It is a very simple circuit. It’s clearly live as it is working almost. If the lamps illuminate when the switch is turned each direction then the wiring would also appear to be fine. I think this is a lamp issue.
I’ve emailed you directly regarding this. I seem to remember your bus is in the Camden area. Im going to Canning Town the week after next if it can wait until then.

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

Is your bus refurb or original?

If original, indicator bulbs are 2 x 12v wired in series.

If refurb, the indicators are 2 x 24v in parallel.

If both bulbs are not identical, one or the other won't work.

Are you sure you're not trying to use a dual filament stop/tail bulb? This will cause problems as no circuit is being made.

My bus number (if any): RML2532

My bus number (if any): RCL2559

Sounds like a good clean up and checking of all terminals and connectors might clear this issue up. Check that both sides are wired the same way. Check the wattage on your flasher unit and ensure the total wattage per side for the flasher unit match the bulbs used. Cheap bulbs also can upset things as they aren't the wattage the claim to be. (Learnt that one the hard way). Check the indicator switch contacts are clean. Bad connections can reduce the voltage and become a bigger problem.

Depending on location I don't mind looking. Either that or email me clear photos of the lamp holder wiring side by side and I will see if I can spot anything if you are still struggling.

My bus number (if any): RM2151

Hi robert. I’ve emailed you from my work email

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