Well I have a late 70s dodge drive train in my project truck (with electronic ignition) and as the title suggests, the battery just keeps going dead. So I ran some ammeter tests to see if I could find the culprit. Each of the following tests were independent. Key ACC: 1.8 A Key OFF: 0.01 A Key RUN: 9.8 to 10.25 A So i suspected the problem occurs in the RUN position, so the following tests were done in the RUN position. unplugged gauges: 9.5 A unplugged electric choke: 9.4 A unplugged electric bowl vent: 9.8 A unplugged ECU: 4.5 A unplugged voltage regulator: 8.5 A unplugged ECU, VR, Ballast resistor, Starter relay: 3.5 A The truck runs fine once started, and doesn't indicate any ignition problems, but the battery just goes dead all the time. I added ground straps from body to frame, alternator to frame, block to frame, ECU to body, and trans to frame before these tests. Any suggestions?
Also, when pulling fuses, nothing dropped the amps below 8.5 A, and only the radio, gauges, and coil seemed to affect it at all.
One more word now that I think of it, I am running a 5 pin ECU, only using 4 pins, and a single ballast resistor. Could this be a problem?
Does the ammeter show a charge when running? If it does, charging is not the problem. If it is charging ok then there must be a current draw when stopped. The .01 amp. Try connecting a 12v test light in series with the + battery cable. Then pull the fuses one by one till it goes out. Don't forget the dome light it will be on if you have the door open.
The 5 pin ECU's are interchangeable with 4 pin the 5th pin was a ground for remote mounted units in some RV's. Running a two pin ballast resistor, have you tied the start and run sides together? Posted using the Full Custom H.A.M.B. App!
When is the battery going dead? overnight ? while driving? or sitting in the driveway idling? Have you checked alternator output at idle and at highway rpm?
The voltmeter on my gauge cluster shows 14 to 15.5 at high (cold idle) and around 13.5 at idle. I tried pulling all fuses to see current drop, and it never fell below 8.5A, so maybe it is not a fused circuit thats drawing? I have the dome light disconnected at the moment. I will double check my ballast resistor wiring today. The battery will go dead over roughly two days of sitting, and a lot faster if I am messing around inside with the radio, or key ON, etc.
Unless you don't have enough alternator you should be able to run every circuit in the vehicle without sapping the battery. So you have three things to look at, alternator output (before and after the voltage regulator), the charging cable/wire ( somehow current has to get to the battery) and the battery itself.
I forgot to mention, all the tests above were with the engine not running, except the charging (voltmeter) tests.
Charging voltage at 15.5 seems high. Most top out at 14.5 or 14.6. If the battery is getting overcharged it might be internally discharging. Try disconnecting the battery to see if it still goes dead. I checked out one woman's car because her battery kept going dead right after she bought a new one from Walmart. They had replaced the battery once after checking the car. She asked me to check it when the second one went dead. It was charging at 14.5 and no draw so she took it back to Walmart where they put a 3rd and finally a 4th battery and that cured it.
What happens if you remove the ground cable when you put it away for a few days? Even At 0.01 amp draw a fully charged 64 amp/hour battery hold a reasonable charge for months. I'd charge the battery at 5 amps or so for a couple of days and have a load test done. I think your battery may be forniscued.
My thought is a bad battery as well. A 0.01 Amp draw with the key off shouldn't go dead in a couple of days.
Try this, may have misunderstood your problem. After you shut the vehicle off and with everything turned off pull the ground cable. If it sparks you have a current draw, or a short. This doesn't work a late model car by the way because everything with memory needs current all the time. if no current draw while it is shut off and the battery is going dead after a day or two the most likely culprit is a weak battery. if it is any consolation I went through 4 batteries in my old willys pickup before I got a good one. After the 3rd in the first year I just bought a better quality battery and cut my losses.
If removing the battery cable stops the discharge try disconnecting the output wire at the alternator you may have a bad diode.
Hmm thank you for all the suggestions. The battery cable definitely sparks when first connecting it. I will check the above mentioned things today. Doesnt 10 amps with the key on seem really high? I though it should be like 3 amps. I also didn't realize that there were so many bad batteries out there. The alternator is new as well, I will check it though.
okay I haven't pulled the alternator wire yet, but I thought I would throw my wiring diagram up for scrutiny. It looks a lot more complicated than others I've seen. Ignore the strange color descriptions my girlfriend wrote down when I was barking out colors from under the dash.
Disconnect the main power wire at the alt. and then see if the ground cable still sparks at the battery. BTDT
Let's not make this harder than it is. There are only 2 ways the battery can be going dead. We have eliminated alternator so that only leaves one thing, something is drawing current when the car is shut off. You say you get a spark when you connect the battery, that confirms something is drawing power. So put a 12v test light between the battery post and cable and see it light up. Now go around disconnecting things until it goes out, boom there's your problem. Start with the fuses (easy). Don't forget, if the door is open the dome light will be drawing power (unless you shut it off). If no joy, try disconnecting the alternator. Keep on until you find the short.
Fucked diode in the alternator, replace it, also, Chrysler charging systems regularly charge 15.5 volts, has something to to with it being a solid state unit. Seen it lots, just did a 29 dodge, 360 engine, bad diode in alternator, and after all summer and 3000 miles, still charging 15.5 volts, hasn't cooked the battery.
I did a current test on the main power feed of the alternator, 0 amps with key off and in run position. I'll do the spark test real quick.
Spark test results: with alternator output disconnected, still sparks (makes sense for things like radio memory). And I already did the fuse test, and nothing would "make the light go out."
Are you removing ground cable and getting spark? Solution to a similar problem on car w/GM alternator - alt trigger wire and discharge light wire had been reversed. Check out this thread for possible testing help. http://www.jalopyjournal.com/forum/threads/how-to-use-a-multi-meter-volt-meter.960762/
Just for shits and giggles and peace of mind take your volt meter and connect the + wire to the + post and touch around on the top of the battery to see if you are getting a voltage/amp leak across the top of the battery because of dirt or moisture. I had a student's pickup that had a battery that would go dead in less than three hours because of the high current flow across the top of the battery. Last make sure that someone isn't playing the damned radio when you aren't around.. Had a student that had that happen on his low rider when his ding dong little brother played the radio and ran the battery down while he was at work every night. Battery only went dead when he was at work and the car was at home.
I just wanted to follow up with this thread and confirm I have fixed the issue. Here is what I found. -The 10 amp fuse in my multimeter blew sometime during my diagnostics which is why I couldn't reproduce my results -This problem was tied in with my running lights not working which was nice -So the culprit was a relay that was energized all the time due to faulty wiring in the park light circuit. And here is why it was so hard to detect. --Not a fused circuit (relay is powered all the time), so the above mentioned tests wouldn't have found it. --When hooking an ammeter up, it would spike initially due to the relay closing, then drop to almost nothing because it resulted in a short. --Still got 12v to my light circuit, but when i hooked a bulb up, the extra load from the relay dropped it to 9v at the socket, so it wouldn't light. It took two days of painful wire tracing through the entire light circuit, but now, all my electrical works. Just thought I would share my results. So in conclusion, when you do the fuse test, pull your relays one at a time as well!
Congrats! It appears you have a much better understanding of your car's electrical system, now. And I know something I didn't before...
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