Friday evening, after backing my Olds out of the shop and washing it, I attempted to start it back up to leave but it would not crank. I hooked up the charger and it started right up just like it has always done since I rewired it and converted it to 12 volts, I noticed that the indicator lamp never went completely out, it was a very dim and that the stock amp gauge never moved. Saturday I attempted to start it and again it would not crank and I had to put it back on the charger. After charging the battery, I checked the battery voltage with a ohm meter and it showed 12.4 volts. I restarted the car and rechecked the battery voltage, it was still at 12.4 and remained 12.4 no matter what the speed of the engine was. I then checked the alternator at the battery post (at back of alt) and it showed that it was putting out 14.5 volts. The indicator lamp still flickered dimly and the amp gauge needle never moved. Obviously, the alternator isn't charging the battery. Anybody have any thoughts on what might be causing this? Here is a similar diagram of how it is wired... I have a 10 ga. wire running from the bat lug on alternator to the starter. A 12 ga. wire running from alternator post #1 to a indicator light and then to the ignition switch and then onto the starter solenoid and another short 12 ga wire going from the #2 post back to the battery post on the back of the alternator.
^^^^^ Agree, primary feed from battery to starter's battery post. But to be certain check both sources. Alt to starter. Starter to Bat. By the way, where did you connect your negative test probe at. Battery negative post or ch***is ground?
Had the same problem last year. The wire was loose on the junction block. Check all connections. To test i ran a wire from alt to battery . worked fine.
Could be bad connections or a bad battery, too. I’ve seen batteries do some crazy things , over my years! Bones
Also check all grounds. Battery to engine, engine to body, engine to frame. Doesn't hurt to run a separate wire from the alternator case to where the battery ground fastens to the engine.
Did you fully charge the battery or just use the charger to jump it? A good fully charged battery should start a rig a number of times without a charging system even on it. Just jumping it and backing it out of the garage and shutting it off isn't going to put a viable charge in the battery even if the wiring is all working correctly. Still it should show a charge at the battery when it does show a correct charge at the alternator meaning that as mentioned earlier the wire from the alternator to the starter post has a connection issue somewhere. I'd go though the whole starting and charging wiring systems. Clean the battery posts and check the cables for corrosion where the cables meet the ends on both ends. Make sure that the ground cable has good contact with the block. Check the full length of the wire from alternator to the starter post. Make sure that the top of the battery is spotlessly clean so you don't have a parasitic loss across the top of the battery. (not a bad idea to hook the multi meter to one post and touch around on top of the battery to see if you are getting a voltage reading showing current flow across the top in any ac***ulation that may be on top of it. I've seen a nine volt drain across one battery that would go dead in two hours. Last, are you leaving the charger on the battery long enough to actually give it a full charge or are you just giving it a surface charge while you jump it?
All good advice, but I'll throw out a couple more possibilities... All electrical issues are either a failed component or a bad connection, ***uming the original install is correct. The alternator is putting out 14.5V, so it's a bad connection. First, fully charge your battery and verify it's good. If the charging system is attempting to charge the battery, the high charging current will skew the test results. Using your volt meter, check the wiring point-to-point to find it. Do this with the system operating under 'normal' load. Check from the alternator output terminal to the first connection. The meter will show voltage loss between those two points directly; you want under 1/2 volt. Checking between the attaching lug and the wire terminal will show a bad connection also. Keep in mind you may not find it all in one place, I'd check every connection. Do the same thing with your ground path. Do you have a low reading (again, under 1/2 volt) between the alternator case and the negative battery terminal? If not, there's an issue in the grounding, could be a poor electrical connection between the alternator case and its mounting bracket, bracket to motor, etc... One last suggestion. The 'secondary' wire from the alternator that you show connected to the same point as the output should be connected to 12V at the fuse panel. This is your 'sense' wire and it's purpose is to compensate for voltage drop in any supply wire between the battery and the rest of the system.
And remove the charger when the engine is running. The gauge will not show a charge when the engine is running if a battery charger is still connected. This just happened to me last week. Replaced the alternator, started the motor and no charge on the dash gauge. Then noticed the charger still connected, disconnected the charger and the dash gauge immediately went to charge.
Mystery solved! I checked everything out and couldn't find anything wrong, so I decided to run a jumper wire from the battery lug on the back of the alternator to the positive post on the battery, checked it with my ohm meter and it showed the battery to be getting 14.5 volts, unhooked the jumper and it went back to 12.4 volts. Made up a new wire and , now, everything is working as it should. I want to thank you all for taking the time to reply to my question, it is very much appreciated...
Glad you found the problem. One thing not mentioned is the size of your alternator. If it's a high-output version (above 60 amps), I'd suggest upping the wire size to at least a #8, maybe even a #6 to reduce stress on the wire.
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