AS a guess, when you pulled hard on the speedo camle under the dash, you disconnected a power wire to the headlights (and maybe others as well) and its now grounding somewhere. Find it before you drive the car this way, or major problems may occur- including a fire!
And as JB said, if moving the ammeter wire causes changes, thats a separate but also very serious loose-connection problem that can and has resulted in fires.
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