Tachometer acting funny

[data89]

1st...my tach was running normal. I already had replaced most of the bulbs in the cluster with LED, but not the tach bulb yet. I had a problem with the gas gauge not registering and so took out the dash cluster and solved that problem.

While I had the cluster out I installed an LED bulb in the tach and bench tested it, so all the bulbs on the cluster and all gauges worked.

I put everything back together and started the truck ('69 Chevy C10 stepside) and there were tiny sparks showing in the tack when the lights were turned on. While revving the engine to check the tach they went away, BUT, now the tach will not go to zero either with the engine off or just idling. It stops at 2000 low end. It does indicate rpm's from 2000 to about 8000 whereas it used to go from 0 to about 6000 rpm.

What's going on with that???