if you suspect a voltage loss on the circuit, you can perform whats known as a voltage drop test. first, test the voltage at your coil/ignition. if its lower than your battery voltage (if they differ by more than .5v) you can slowly eliminate parts of the circuit until the excessive resistance is found. I will say before I explain this, that intermittent electrical problems are the devil hahaha. so if the problem is active its much easier to find. so with a voltmeter, test from positive on the coil to positive on the battery. if you get a reading of .5v or more, leave one lead on the battery and move the other lead down the circuit until the reading goes away, this will help you find the area of the circuit in which the unwanted load exists. do the same for the ground side.
As far as intermittent problems, these are usually intermittent opens/high resistance, or intermittent shorts to ground/voltage (two wires rubbed and touching eachother or frame).
To find these we can do a continuity test, using an ohm meter. now using an ohm meter requires POWERING DOWN the circuit. failing to do so will blow your meter fuses, or possibly fry it. Personally, I like to make my apprentices buy me donuts every time they blow a meter fuse, that way they learn
so on the UNPOWERED circuit, place on lead at the coil on the positive side, and one at the positive lead where it would hook up to the battery. essentially with the circuit closed, you want as close to zero ohms as possible. if you have O.L. (out of limits) your circuit is open. if you're getting a good reading (.2ohms for example) manipulate the wiring harness and watch for changes in your reading, especially connectors. for example, if you wiggle a connector and your resistance jumps up to 10 ohms, you have a poor connection there. this can be done on any circuit as long as its POWERED DOWN (cant stress that enough). you can also do continuity tests between two circuits if something is staying on when it shouldn't, to see if its finding power/ground from another circuit.
Shorts to ground are usually indicated by blown fuses. This tells you that the power feed has found a ground before the load, therefore making the fuse a very brief load (they dont like that haha). The same type of test can be done with alittle variation. install one lead to your power feed circuit, and the other to battery/chassis ground. you should read O.L. (out of limits). if you have a resistance reading, find your short by moving one lead up the circuit until you find O.L. if you dont, but suspect something intermittently grounding, manipulate the wiring harness and look for a resistance reading of any kind to pop up on the meter. if so, you have a wire touching frame somewhere.
If you are unclear on any of that, please let me know and I will try to explain it better.
