Electrical System Hot, but no spark
by Jeff Zepp
A. There are three wires to the coil, the high voltage (thick) one that Dylan mentions that goes to the center of the distributor cap, and a plus and minus. The plus is always hot when the ignition key is turned, through the ignition switch and fuse block. The minus goes either directly to your points for earlier models, or to the ignitor on later years, which just amplifies the current from the points (or electronic ignition) prolonging the life of the points in the non-electronic ignition models, or simply making life possible for hall-effect ignition.
The coil makes high voltage by charging a magnetic field when current flows through the primary (points closed), then when the points open (or current is otherwise interrupted), the field collapses and causes a large voltage to build up on the secondary. When it does, the spark shoots from the coil to the rotor to the closest connection inside the distributor cap, which then goes to a spark plug.
If you have points, verify that they are adjusted such that they are opening at all. I have seen FJ40s that have supposedly been set to the proper dwell angle with a dwell meter that were only opening .003" and hardly would run at all. I think spec is about .018", or the thickness of a matchbook cover. You have to take the distributor cap, rotor and dust cover off and turn the engine until the points are open as far as they will go, on one of the apexes of the hex-shaped points cam, assuming you are still running the stock I-6, be it F or 2F. If you are running a V8 it will have 8 sides.
If everything is dry, and the points are opening okay, the coil would be the next culprit. They are easy to test and inexpensive to replace. The primary should be neither open or short, maybe tens to hundreds of ohms. The secondary should also be neither open or short, thousands to tens of thousands of ohms. I just checked the Haynes manual and they give no figures, but bad coils I have seen are always open or short, usually on the secondary from long use, or on the primary if it sat with the key turned on without the engine running.
The ignitor can fail too, but it is easy to bypass. Just wire directly from the points to the negative terminal of the coil.
You haven't mentioned the year or model cruiser that you ask about, or whether it has a stock engine.
1971 FJ40, 1976 FJ40, TLCA #4063