Re: '84 8.2T marine starting problems
Measuring voltages at "way points" such as switch and solenoid connections is a good and valid way to tell what volts are "available" to that device. But, it won't tell you what amount of volts that device may be using or "robbing" from that circuit. Your volt meter can be used in a very effective way to identify bad components such as switches, wires, cables and even poor connections in a circuit by taking "voltage drop" readings. The concept is simple:
Ideally, the "load" in the circuit should be the only thing in that circuit to "consume" voltage. Let's look at something simple, a 12v motor hooked to a 12v battery and controlled with an on/off switch between them. One wire from Battery+ post to the switch with another wire from the switch to the motor's Positive terminal. Another wire from the B- post to the case on the motor for ground. A complete circuit. With the only item in that circuit intended to "consume" voltage/current being the motor itself. That's the theory. However, that's not what is actually happening.
The wire in the circuit, in fact, will consume a very small amount of the current because of resistance. Each and every connection in the circuit will also contain a bit of resistance and "consume" some current as well. It's all because nothing in our world is perfect, not even new wiring or new switches or pristine connections. But, we can use the voltmeter to make sure that each connection, wire, cable and switching component doesn't take too much.
If, for instance, you take your voltmeter leads, while on the 12v scale, and touch each terminal of the start switch you will see 0 volts. But, when you activate the switch, you will get a reading (assuming you are using a quality instrument) of "some" voltage. Ideally, it would be zero volts but close to zero is real and acceptable. Let' say your meter reads .015 volts (15 millivolts). That is considered acceptable. A reading of anything over .250 volts (250 millivolts) would indicate a failing switch with too much resistance across the contacts.
Here's the cool part. You can then take your leads and place them on each side of every connection in that circuit and read how much each connection is consuming. You can connect the leads at each end of a wire and determine if that wire is conducting current with little resistance or if it is internally damaged and is acting as a load instead of a conductor. You can place the positive lead on the battery post and the negative lead on the positive cable end right next to it and directly read how well that "interface" of cable and post is conducting. A low reading means a good, clean, tight connection at the battery and a high reading means take it off, clean it and put it back tight. I hope this is making sense to you as this is probably the way for you to find your problem.
Here's the rub; these tests only work when the circuit is operating. You need to connect your leads and then ACTIVATE the circuit to take voltage drop readings. So, you may need an assistant. This is one of the ONLY ways to ACCURATELY identify a bad battery/starter cable.
A 000 or 0000 cable has many small wires twisted together to form the large diameter cable needed to deliver AMPS to the starter motor. Many mechanics still use an ohmmeter to test these cables for conductivity. That doesn't work! All of the wires in that cable could be broken except for one and you will get a good resistance reading on an ohmmeter. But, if you do a voltage drop test across that cable, you will get a high voltage reading and that will tell you that the cable is bad.
Volt drop testing is valid anywhere in the circuit. Positive side or ground side doesn't matter. It will ALWAYS tell you exactly what is happening across connections and components even if that component is a ten foot long piece of steel used to hook the ground strap to.
I hope I didn't confuse you and I will be here to help you with the concept if you need it.
I have a 31' Chris Craft Commander with twin Detroit 8.2T's. It is 12V. The problem that I am encountering is that I cannot start either engine from the start buttons. When I try to, I turn the key switch and hear the fuel solenoid click on and hear the oil pressure buzzer as I normally do . When I press the start button all I hear is the starter solenoids clicking and the engine does not crank. At first I thought it may have been that the batteries were to low to activate the starter. I charged them up and still nothing. I load tested them and they checked out fine. With a voltage meter I tested at different points. At the solenoid, key switch, and the start button I measured 12.7V. When the start button is pressed the voltage on the button drops to 6.5V to even 3.4V. I can however jump the solenoid and crank the engines over and run them. I tried to run a new solenoid wire from the start button back to the solenoid and jumping over the button and key switch all together. None of which worked. I also disconnected the wiring harness in the engine compartment. With a key starter switch with alligator clips on the 2 wires, on the engine side of the harness, I made a connection between the power and solenoid wires. I turned the key and the same thing happened. All I heard was the solenoid click. I checked the wires for breaks or damage and found nothing visually wrong with them. I changed all connectors and cleaned up all the terminals. I bought 2 new solenoids and rebuilt the starters. I also isolated the starting system and made sure there was nothing else stealing power of it.