Here are some notes from test that I did several years ago on the BW overdrive.
One of the most frequent problems in a BW overdrive is in the electrical path to the solenoid that kicks in the overdrive. Power for the circuit starts at the ignition switch and in many cases can have a drop in...
I have a starter solenoid on my 35 and use the lighter as a starter button. When I push it in it grounds the circuit. Its been a while but I did have to modify the lighter to keep it from staying in when pushed.
looks like you will have to remove the c clip that holds the spider and with the horn rod in the off position, install the spider with the tabs in the vertical position.