Radio - Voltage Drops When Light Connected

[George]

I'm having a hard time figuring out why my two light bulbs found on the radio are very dim. I'm also dim when it comes to electronics so I know how the bulbs feel. 

 

I bought a replacement 12V light bulb for this one.

 

 

 

When I test it on a car battery charger and a 12V battery it works and is bright. When it's wired up on the radio it's very dim. The wires tested without the light bulb connected read 10.8V but when the bulb is wired up the same wires read 1.5V. What the what the?

 

This other light bulb (below) is also suitably bright when tested independently but also exhibits the above issue when connected. In fact, this one is puzzling me even more and could explain my problem... The negative wire leading out of the radio leads to the positive terminal for the light bulb. The casing for the light bulb is screwed on to the radio chassis. I know the light bulb doesn't care about positive and negative but I'm really confused about how this bulb draws it's power. When I reverse the polarity the light bulb is very bright but the other one doesn't work. Does this indicate an issue somewhere?

 

Also, without the large bulb connected the other light bulb does not work...

 

 

Earghblergh. I'm confusled. If the above makes no sense and isn't clear enough for someone to provide help I'll just take it in to an electrician at some stage.

 

Cheers

[George]

Eureka!

 

I told you I was dim with electronics. Both the wires leading out of the radio are positive and of course the chassis is negative/ground. Sifnt remember that George.

 

So now that it's all wired up properly the large light is bright but the small light is still dim. It's now putting out 3.4 volts so I'll just need a 3V light and I should be good.

 

Thanks for the help. You're all good listeners. ;-)

[gav240z]

I take full credit.