Yeh the thin wire is the gate. If you disconnect the gate you can probably test the scr in situ with a meter. This page has some good information and diagrams:
The Silicon-Controlled Rectifier (SCR) : THYRISTORS
Depending on the device you can wire a resistor between the gate and anode and it will fire manually. This would at least prove that the scr is ok and the problem is in the firing circuit.
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Now, Cole, when you shift the gear and that little needle on the ammeter goes into the red and reads 2000 Amps, that's bad.
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