Here's what I did for the Reverse solenoid on a T56 conversion
You will need to go to the local U-Pull and cut a pigtail out of the harness [the plug and some wire still attached] If you don't have one in your car.
And grab another stoplight switch to use on the
clutch pedal while there.
The solenoid itself is a simple 2 wire electromagnet , it can be wired either polarity [ + and Ground]
Tee off a power feed
from the stoplight switch [after the switch] over to the other stoplight switch mounted on the clutch pedal then to the solenoid.
They must be wired "in series"
With your foot on
both the brake and clutch pedals you can select reverse,
BUT
when upshifting your foot isn't on the brake pedal [no power feed] so reverse is still locked out.
[We don't do this in Road Racing because we can be hard on the brakes at 150 mph downshifting into 5th.]
But on the street 90% of 5th gear downshifts on the highway is doing a passing move. [6th is a cruising gear only]
I did this ^^^^ on my friends pickup with a T56 conversion.
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I have another friend ,who used a simple "Summit Racing" RPM switch that had the mode set to be normally open after 2000 rpm.
So below this rpm the circuit is closed and provided ground for the solenoid.
They then selected 4 cyl mode on the switch.[ A 4 cyl @ 2000 rpm has the same pulses as a V8 at 1000 rpm]
So you can automatically select reverse when the engine is idling.
The circuit was
Ign power to Clutch pedal switch to Solenoid [12 v +]Then from solenoid to rpm switch to ground [the rpm switch has a ground wire]
here's the switch
https://www.summitracing.com/parts/sum-830449-1
and the instructions
https://static.summitracing.com/global/images/instructions/sum-830449-1.pdf
The rpm switch can take a 3 amp load and the solenoid draws 1-2 amps.
By using a clutch switch there is no amp draw if the engine is idling in neutral for extended periods of time.
Maybe his is a better idea.[ But understand , his engine uses a normal distributor for the RPM switch]