1981 Dt 175 burning out light bulbs

No since the only thing that leaving the key on should cause is a flat battery and on these bikes the battery powers all lights except the headlight. The headlight runs directly from the motor, and the ignition is completely seperate and does not involve the battery. The original voltage regulator has only one wire and earths out where it is bolted to the frame and is only connected to the power heading to the light on/off switch. So unless the bike is running the headlight will not normally light up (you will get a glow when kicking the motor over). My advise is remove the plug and check for spark, then kill switches, then plug cap, then wire connectors until you do have spark

Warren78102 said:

Thanks for the information. I wonder why it burned out the bulbs, head light, tail light and the bulbs in the tack, speed odometer. What’s weird is it was working fine then I changed the battery out it would not start so I changed the voltage regulator still won't start.

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Are you using the rigth battery which should be a 6 volt battery and when you changed it did you used 6 volts?.
More then like you had setup up wrong and burn up something.
It could even be bad set of points also there should a line fuse on battery cable besure check it.

It might be worth a trip to K Mart to buy a $10 multi meter so you can check the voltages. Headlight 7.5 volt max AC with the regulator working and all the others battery voltage DC. Open circuit voltage (wires as they leave the motor and not connected ) around 30v AC. Lots of these older more primitive lighting systems need every bulb in place and working and the rectifier sending current to the battery and all connectors clean and the earth clean to prevent surges and more blown bulbs in a chain reaction. If you only use/need the headlight you can remove or ignore the rest without causing any harm.