The later model buil-in diagnostic led/sw pulse
circuit uses a switched ground and B+ to feed the
LED.
That way , you are counting the flashes vs the spaces.
Also better in the sense that you know you have the circuit with the push of the switch.

Bob Terry,
Yes, I would be interested in seeing your auto circuit.
If you email me , I will send you the connector pin-outs.
Thanks
AJDalton7@aol.com