General Front turn signal bulb burning out

[bmdfiat76]

Hi all. We have been tinkering with our 1976 fiat spider in our spare time mostly cleaning up bad connections. One thing that puzzles us is with the left front turn signal not working. We replaced the 1154 bulb that was in it with an 1157. The bulb came on and the signal worked but the filament continued to glow between blinks never really going out completely between blinks and then burning the new bulb out in less than a minute. Appreciate any input.