Re: How and where to mount a ballast resister on a 1976 Chrysler 75hp model# 757HC
It would help to have a photo posted.
However: Yes, the resistor will get hot. It does have some current (meaning amps) passing through it. That is its job. It takes 12 volts and drops it to about 9 volts to increase the life of the coil. The extra 3 volts is shed as heat. Depending upon the resistor, again, yes one side is attached to the power source--in this case, the blue wire from the ignition switch. The other side is attached to the positive terminal of the coil itself. Mount it away from other wires because the heat can degrade insulation.
If it has 4 terminals, one set may be the bypass side (explained later. However, I am not that well versed in old auto electrics and you would need to check with someone else as to what terminals do what job.
Typically, when an old auto is started, there is such a large load on the battery that battery voltage drops to 9 volts. SO: to get full power and spark from the coil (for positive starting) it is designed to use 9 volts. When the engine starts, voltage returns to 12 volts which is too much for the coil so a ballast resistor is put in line.
NOW: If the ballast resistor is in line at starting, the already low 9 volts will drop to about 6 or so. THUS: On autos, a starting bypass is also incorporated in the circuit to maintain 9 volts at all times.
A smaller boat engine will not or may not drop voltage to 9 volts at starting but it still will drop it some.
ALL this to say: If you have trouble starting with the ballast resistor in the circuit you will need to incorporate a bypass too.