timer + transistor question

[ozbaz]

I have made up led turn indicator lamps for a verry old car with a 6 volt system, and a "flasher" unit using a 555 timer driving a pnp transistor(MJ2955). Output from the collector goes through the direction switch to the left or right lamps, and there is a piezo buzzer between the output and earth. The switch is dpdt and was used so one side can switch on the power to the flasher. It works fine on the bench, but I find I will have to switch the negative side of the battery supply instead of the +6volt side otherwise the buzzer works all the time.
This leads to my question: if there is always 6 volts to the 555 and the emitter of the transistor, will there be any harm done to the components, or current draw from the battery, even though there should be no load on the flasher, (except possibly the buzzer?).
I just don't want to fry the chips.

[I_Daniel]

As you have not given a circuit diagram I can only guess at how the Piezo buzzer is connected which is a useless exercise.
However you could try connecting a diode from the right and another from the left position of the indicator switch and connect the Piezo to them. The anode-cathode connection to these two points depends on whether it is a negative or positive earth system.
Remember this is on the globe side and not the central position which switches power to the left or right.

In 1972 on my Taunus station wagon, 6 volt system, I used an oscillator and connected the power to it as described above and it worked perfectly. Two 1N4001 diodes should do it.

As you are using a double pole relay to switch the power on to the 555 power to the MJ2955 will only be switched on by the 555.

[ozbaz]

Hi, Thanks for the interest and reply. I have solved the buzzer problem, but that is now the least of my problems. With the unit in the car it does everything right, until I start the engine. Then the electronics go beserk, so now I have the massive job of isolating them from outside interference. So that's a matter for possibly a separate post?

[I_Daniel]

All I can think of is the power supply may be fluctuating or it needs a choke and two capacitors to decouple it.
Check where your power comes from. You may have it connected to the lead that goes to the coil.
Try connecting it to the same supply as the radio (If one is installed)