904 differences

Good deal on the seal and I learned something as I thought all 904's used the same seal. Yeah you can jump the neutral switch to test it although if you just jump it at the trans. you also have the wiring leading to the starter relay that can cause an issue. If you look at the starter relay the 2 small prongs are the ones that kick it in. One side leads to the ignition switch (yellow on my 68 Cuda) and the other leads to the neutral switch (brown on mine). If it doesn't start by jumping the neutral switch try jumping the corresponding color wire at the relay that leads to the neutral switch. If it still doesn't start it's a bad relay, starter, battery or cable.

p.s. if it does turn out to be a bad neutral switch make sure and fix it right. Jumping it out may get it working but is really dangerous. My car was jumped out when I bought it and I didn't know it and one day I didn't notice I had left the shifter in low to give me access to the stereo and I started it and nearly ran into my work bench before I got it stopped. I'm extremely glad no one was in front of me.