Had the same problem on my GTX. The switch fixed it.

But...I did an aftermarket switch first and that didn’t fix it, splicing the wires. Found a NOS piece and it worked, so not sure what happened. I did check the connector (might be a good thing to check).

'69 Hemi Charger 500, ‘70 U code Challenger R/T
(These and a bunch others at www.dkowal426.com)

P.J. O'Rouke: "The old car ran perfectly, right up until it didn't."