I have a reoccurring problem with my indicator lights I have discussed here before. It is a problem which has baffled a couple of electricians.

The odd thing is if you connect the wires to the two points on the bulb at the back, the front light flashes on that side. which indicates there is power going in one point and out the other, yet the bulb, which I have tested on the opposite side does not light up at all.

We have tried various combinations and there is only one that sort of works. If you put a 5 volt bulb in the front, the front lights up but not as brightly as before, and the back flashes a. a suitable brightness. Replace the 5 volt bulb with a 12 volt (tested) bulb and it lights up, but the back indicator fails.

Reading from the two wires on the back drivers side is 24.6volts so there is power there.

I've been advised I will need to remove the dashboard to get at the relays and do something or other, perhaps replace them.?

For the record the relays appear to be working fine.

Having been advised to replace the starter when the problem needed new batteries, I am reluctant to start taking things apart. With a 5 volt bulb all the indications are working, but the front drivers side is not as bright.

So we have a working 5 volt bulb up front and all else is normal.

The 5 volt bulb is connecting. Why should a 12 volt bulb in the front cause the rear drivers side to fail?

If any of you have experienced similar problems, I would be grateful for your input.

My bus number (if any): RCL2259

5 Volt or 5 Watt? I'm not aware of any automotive SBC 5V bulbs and I've just trawled through the Lucas automotive bulb catalogue. 6 volt, 12 volt, 24 volt and some specials for higher voltages but no 5 volt bulbs of any description.

Have a look at the link which although a little complicated to follow describes what happens to a series circuit if the Wattage alters.

http://web.physics.ucsb.edu/~lecturedemonstrations/Composer/Pages/64.36.html

If the fault is on both n/s and o/s indicators I would have a look to see if anyone has fitted a NON insulated-return indicator warning light bulb holder.

This was a professional which I do not wish to embarrass, but he was definitely talking volts and comparing the usual 12 volts to the 5 volt bulb he provided from his kit. The bulb had the same boyonnet fitting as the 12 volt, but the glass bit was shorter by half, as if the bulb end had been trimmed off, and it was white, not clear. It is still on and flashing dimly when turned on.

Maybe he confused watts and volts?

I followed your link and must admit I don't fully understand what needs to be done.

I keep reminding myself that this was all working with the 12 volt 21 watt bulbs before the back right light failed and a solution should not be complicated. I'm worried if I mess with different combinations it might be a bit overkill.

What would you do. I value your opinion.

My bus number (if any): RCL2259

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

Your email is rejecting messages. I am grateful for your offer but can't seem to get a message to you. I am away for the next 4 days. Will try again when I get back. I think my email from the forum is working.

Wishing you well

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