By your pics it looks like its been converted over to a ministarter and the wiring is not correct. here is a diagram that should help: A typical solenoid: Ministarter before and after wiring: The mini starter requires more current to energize the solenoid on the starter because it not only closes the contacts to spin the starter motor, it has to mechanically throw the bendix into the flywheel. The reason your car starts intermittently is likely because your ignition switch is going bad. The way the fender mounted solenoid is wired (by looking at the picture) it is only being used as a terminal tie point. It is not carrying that extra current required to energize the solenoid on the starter and it’s starting to take its toll on the ignition switch contacts. Other things you can look for (since you said your battery is in the trunk) is a heavy battery cable ground from the engine to the body and clean tight connections. Also in the trunk, look for a good ground from the negative battery terminal to the body.