I can share a few comments of value. First, forget Haynes and Chilton manuals for anything electrical. In the rare event they have any wiring diagrams at all, they do a very poor job and are never complete. I prefer manufacturer's paper service manuals, and when it is the only other thing that is available, I will use online manuals.
The five milliamp draw you found is fine. The industry standard for vehicles with radios and computers with memory circuits that must remain live is 35 milliamps. At that rate, Chrysler says a good, fully-charged battery will be strong enough to start an engine that has been sitting for three weeks. There are a few exceptions, Cadillac being one in particular, that allow up to 50 milliamps.
A fuse link wire will not be intermittent unless it has a corroded splice on one end that is making intermittent contact. That is pretty much unheard of because those splices are always sealed with heat-shrink tubing with hot-melt glue inside. Where some less-informed people can run into trouble is when a fuse link wire burns open, it leaves a carbon track behind inside the insulation where the arcing occurred as it burned open. That carbon tracking can conduct enough current that a voltage can be read by a digital voltmeter if there is no other load on that circuit. To say that a different way, (lets use an electric radiator fan circuit as an example), if you unplug the fan motor, there will be an open circuit with no current flow. That means no voltage drop across the carbon track, and the voltmeter will see full battery voltage. I have seen really-experienced mechanics put twelve volts to the fan motor and find it runs fine. They already found the twelve volts on the motor's connector, but plug the two together, and the motor does not run. Had they measured the voltage with a test light, they would have found zero volts, not twelve volts, because the test light works on the current flowing in the circuit. No current can get through the carbon track. This is where a test light can be much more accurate than a voltmeter.
When checking the battery's voltage, put the probes right on the battery's posts, not the cable clamps. If there is a bad connection between one post and its clamp, that will falsely make the battery look drained if the meter's probe is on the clamp. When you have the miserable side-post battery, you cannot get to the post while the cables are connected. To add to the confusion, the 5/16"-head cable bolts are not meant to be part of the current-carrying circuit. While you will usually read battery voltage through those bolt heads, if you should read two volts, that is not a reading to be trusted. Remove the cables, then measure right on the battery's lead terminals. Two volts also suggests this was the issue when checking the battery's voltage. If you leave the head lights on for a few hours to totally discharge the battery, it will still measure 12.2 volts. The only time I have actually found two volts is after a battery froze or was left discharged for many months. Each cell is still going to develop 2.1 volts unless it is shorted. It is just that its "internal resistance" will be so high that it cannot produce any current to light a test light. The voltmeter will still see the twelve volts.
The last thing to consider is there may be a bad connection in the area you were working in, and it got disturbed to the point it is working for now. I have been reading frequently about people finding broken connections under fuse boxes. Also, keep in mind GM is famous for using the output terminal on the back of their generators and the large battery terminal on their starter solenoids for convenient tie points for other circuits. If arcing has occurred on the solenoid terminal, it is possible for the starter itself to still work but the wire that taps off that point to have a bad connection. The entire starter system will be dead because the feed to the ignition switch will be bad, but if the smaller solenoid terminal is jumped right to the battery terminal next to it, the starter may crank the engine.
The goal in this case is to get the electrical system to go dead again, and then to be careful to not accidentally "fix" it. Now take voltage readings to see where the twelve volts is lost, but there needs to be current trying to flow in the circuit for this to be accurate. I turn on the head lights, but even that has been defeated on newer vehicles by the insane engineers who cannot do anything without involving an unnecessary computer. Once current is trying to flow, it will be evident where you have full twelve volts and where it drops to something substantially lower.
Given the overall description you just shared, I am fairly confident you had a bad connection right in the area of the battery cables and fuse box. Remember too that if you use the engine block for your voltmeter's ground, that only involves the starter, the generator, and the engine sensors, ignition coil, and injectors. The dash uses the body for its ground, as do all the exterior lights. Do not forget to look at the small ground wire that runs from the battery's negative cable to the body.
Tuesday, March 13th, 2018 AT 6:51 PM
