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battery drain


Dolfinz

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The "relay" is the voltage regulator. The W/B wire is for the field. It should inject current into the alternator when the voltage is low. A failure to produce an output from the alternator could be a problem within the voltage regulator or the alternator.

What makes you think I don't like that grotesque abomination called the Interlock Relay Unit? Have you ever buckled up an inanimate object in the passenger seat because the car would not start otherwise? Seatbelt interlocks came from a push by Ford to make itself look good to the NHTSA about getting people to use their seatbelts more. While Ford had already designed and debugged their system, the NHTSA mandated the implementation of a seatbelt interlock for all cars in the 74 model year. With the relatively short notice most automakers implemented the rules poorly. The NHTSA quickly retired the rule. Here is some reading on the subject: https://www.allpar.com/threads/the-return-of-the-seat-belt-interlock-crazy-rule-or-money-saver.236643/. People found ways to defeat these systems because a faulty interlock would make it where you couldn't drive your car. There is an emergency button under the hood on the passenger fender. There's a picture below. In its early life, the button was red.

Emergency Push Button.jpg

It's an annoyance to have intact, but it won't affect charging.

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Now that I know what you're talking about I disconnected that thing years ago.  I assume that's all it takes to bypass it?  As for my problem, the voltage regulator and alternator are new.  I haven't tried restarting it since I replaced the voltage regulator as it already had a new alternator.  I'll attempt to start it again this weekend and advise if I need further troubleshooting tips.  Hopefully it was an issue with the 47 year old regulator.

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New problem.  When I first tried to start it it was firing but wouldn't stay running.  I had to turn it over several times which was hard on the battery so I let it sit for a bit and put the charger on the battery.  After it had recharged I tried again and now I have no spark at all.  I measured the voltage on the coil and in the start/on keyswitch position I'm only getting 5 vdc.  I assume this is insufficient and I'm baffled as to what could have happened.  It was starting just fine prior to troubleshooting the alternator issue and replacing the voltage regulator, neither of which should affect it's ability to start.  Any ideas as to what could have gone wrong and how to troubleshoot this new problem?

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17 minutes ago, Dolfinz said:

New problem.  When I first tried to start it it was firing but wouldn't stay running.  I had to turn it over several times which was hard on the battery so I let it sit for a bit and put the charger on the battery.  After it had recharged I tried again and now I have no spark at all.  I measured the voltage on the coil and in the start/on keyswitch position I'm only getting 5 vdc.  I assume this is insufficient and I'm baffled as to what could have happened.  It was starting just fine prior to troubleshooting the alternator issue and replacing the voltage regulator, neither of which should affect it's ability to start.  Any ideas as to what could have gone wrong and how to troubleshoot this new problem?

Check the voltage at the battery while cranking. I'll bet it's pretty low, too. You don't say how old the battery is. Maybe you did earlier, but I'm not going back to see. The plates could be sulfated, they can still have adequate voltage while sitting, but they don't have the surface area for the electron flow needed during cranking.

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The battery is also fairly new.  I checked the voltage while cranking and it was 12.3vdc.  The motor is turning over just fine but there's no spark from the distributor at the plugs.  Not surprising since there's only 5vdc at the coil.  What could be causing the voltage at the coil to be so low?

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34 minutes ago, Dolfinz said:

The battery is also fairly new.  I checked the voltage while cranking and it was 12.3vdc.  The motor is turning over just fine but there's no spark from the distributor at the plugs.  Not surprising since there's only 5vdc at the coil.  What could be causing the voltage at the coil to be so low?

I appreciate your willingness to go back and test. 

Let's look at the coil and work back. Fortunately, it's not that difficult to trace.

For stock wiring there should be a white/black wire from the coil to the ballast resistor. There is a black/blue wire attached to the ballast resistor on a different terminal. The black/blue wire goes to a 3 wire/4 position plug and through the engine harness to connector C-5 where it stays black/blue going through the dash harness. The black/blue travels over to the ignition switch where it is energized when the key is in the start position.

So what could cause the voltage to drop?

  1. The ignition switch could be wearing out.
  2. There could be corrosion at one of the three connectors
  3. There could be a bad connector at the ballast resistor or failed ballast resistor.

So what can you do to test?

  1. Measure resistance at the ballast resistor between the white/black wire and black/blue wire.
  2. Alternatively, you may want to test the voltage to ground at the black/blue wire at the ballast resistor with the key in START. If it's 12+, then it's probably the ballast resistor. If it's low, you know it's before the ballast resistor.
  3. Visually inspect the connectors. If they need to be cleaned, a little vinegar on a q-tip can clean off corrosion at the connectors.
  4. Disconnect the connector on the back of the ignition switch and test the resistance with the key in START between the terminals where the black/blue wire and the white/red wires would go.
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This is excellent information, thanks.  I checked the voltage at the ballast resistor blk/blu wire and it was 7.2vdc with the ignition switch on start.  I checked the wht/red wire at the ignition switch and it was 12.2vdc.  When I turned the switch to start, the wht/red was constant but the voltage at the blk/blu was 7.2vdc.  I removed the ignition switch assembly and checked the contacts resistance at less than 1 ohm.  While I wouldn't think this is indicative of a bad switch I am ordering one anyways due to the voltage drop.  I also checked the resistance between the wht/blk and blk/blu on the ballast resistor and got about .1 ohms.  Is this correct?  I will follow up once I receive the new switch.

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The switch contacts should be pretty close to zero. The resistance at the ballast resistor is fine. You don't want the resistance to be too high because that would be a voltage drop.

It does appear that you are losing voltage somewhere, depending upon where you measured the 7.2V on the black/blue wire. Was it at the resistor or the ignition switch? Again, look for corrosion at the connectors for where the dash harness plugs into the ignition switch.

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The 7.2 volts could mean a grounded circuit, either after the ballast or the coil, maybe at the ignition module or along the way to the module. If you had points I'd say check that your points weren't closed.

Edit - p.s. the coil, or the ballast, or wires in the vicinity should be warm if current is flowing, giving that big of a voltage drop.

Just spitballing.  Hard to get a good grasp on the overall picture.

Edited by Zed Head
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I ordered just the module on the back of the switch.  Once I receive it I will install it and if the voltage drop still exists then I will try eliminating the molex connector on the ignition switch and individually connect the wires via spade lug connector to eliminate the connector.  Then, if the voltage drop still exists I will tape up the blk/blu wire and check again with it disconnected.  If there is still a drop then I will run a new wire from the ignition switch to the ballast to eliminate a partial short to ground somewhere between the ignition switch and the ballast.  After that, ????

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1 hour ago, Dolfinz said:

Then, if the voltage drop still exists I will tape up the blk/blu wire and check again with it disconnected.

Shouldn't this be first?

You can't have a voltage drop unless current is flowing.  If you're seeing a drop at the ballast resistor that narrows things down to the ignition system.  Except for the wires that are there as part of a terminal block.  Nissan put extra terminals on the ballast that have nothing to do with ignition.

Really though, if the problem is the battery dying with the key off, you shouldn't be looking for a voltage drop.  You should just be looking for voltage.  There shouldn't be any voltage at the ballast resistor with the key off.

If anyone wants to summarize what the "current" problem is, feel free.  I assumed it's still the battery dying.

 

Edited by Zed Head
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I replaced the voltage regulator as previously suggested because the alternator wasn't charging the battery when the engine was running.  I then went to test the charging circuit with the car running and it wouldn't start.  I determined there was no spark and the voltage at the coil was around 5vdc.  We've narrowed it down to possibly a faulty ignition switch so I ordered a new one.  Once I receive it I will follow all the testing mentioned to determine why all of a sudden I have no spark.  I started at the resistor and worked my way back to the switch and once replaced I will work my way back from the switch to the resistor.  I have no issues yet, at least, with the battery draining when the ignition is off.  Only when the engine is running.  The engine was starting and running fine prior to the 2 weeks it sat waiting for the new voltage regulator other than the charging circuit.  As for the firewall connections, et al C-5, I don't trust any of them as my gauges don't work and I had to completely rewire my headlights, horn, running lights and turn signals.  Once I get the engine running again I will remove the dashboard once again and deal with the remaining issues at the firewall connections.  I've never heard of Vintage connections and I'd prefer to replace the connector if possible.  I will google it.

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Vintage connections has some good replacements for the connectors that use the spade style terminals. The round terminals for the gauges and dash harness to engine harness connectors were made by Yazaki (I think the spade connectors were, too.). Those connectors seem to be made of unobtanium, though you can get the terminals with different connectors from Eastern Beaver. 

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54 minutes ago, Dolfinz said:

it wouldn't start.  I determined there was no spark and the voltage at the coil was around 5vdc. 

If you have the factory ignition module you should see battery voltage minus resistance drop, then it should go to battery voltage after 10 seconds (no current).  For what it's worth.  Not really sure why they call it "locking".

image.png

image.png

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31 minutes ago, Zed Head said:

If you have the factory ignition module you should see battery voltage minus resistance drop, then it should go to battery voltage after 10 seconds (no current).  For what it's worth.  Not really sure why they call it "locking".

image.png

image.png

"Locking" means it is locking out the power switching circuit, so the coil never gets grounded. This is similar to why you don't want to leave the key in ON with the engine not running when you have points, only you are protecting other components.

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5 minutes ago, SteveJ said:

"Locking" means it is locking out the power switching circuit, so the coil never gets grounded.

It says "lock preventing".  I know it's just a translation error.  Interesting though.  There are better terms - current lockout?  Current cut?

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I got the replacement starter switch and installed it.  I also disconnected the blk/blu wire at the ballast resistor.  I checked voltage and now it's 8.5vdc at the connector to the resistor.  I also checked the voltage on the wht/red wire at the ignition switch and when trying to start and it drops from 12vdc to the 8.5vdc.  It appears that the supply voltage is dropping for some reason.  Any ideas of what could be causing this?  Can I just run a new wire to directly feed the ignition switch from battery power?  I'm also uncertain how the transistor ignition unit is related to the starting function?

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3 minutes ago, Dolfinz said:

I got the replacement starter switch and installed it.  I also disconnected the blk/blu wire at the ballast resistor.  I checked voltage and now it's 8.5vdc at the connector to the resistor.  I also checked the voltage on the wht/red wire at the ignition switch and when trying to start and it drops from 12vdc to the 8.5vdc.  It appears that the supply voltage is dropping for some reason.  Any ideas of what could be causing this?  Can I just run a new wire to directly feed the ignition switch from battery power?  I'm also uncertain how the transistor ignition unit is related to the starting function?

There are two things that could cause the voltage drop

  1. If the starter is turning and the battery is not good, you could see that kind of voltage drop. 
  2. There is corrosion between the battery and the ignition switch. From the battery positive, you have a cable going to the starter. It goes out of the starter to a white wire to the fusible link and comes out of the fusible link as a white wire. There it goes through the shunt (for the ammeter) and comes out white/red. The white/red wire goes to the fusible link and comes out as white/red, going to C-5. From C-5 it goes down to the ignition switch. Lots of connections to get corroded. It measures fine with everything off, but when you try to power other things, the corrosion could limit the current flow and drop the voltage downstream.
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So here's what I'm getting.  Battery voltage in static state is 12.75vdc.  Voltage on white wires at fusible link when cranking 9.9vdc.  Voltage at wht/red wires at fusible link when cranking 9.75vdc.  Voltage on battery when cranking 11.4vdc.  Is this indicative of a week battery?  Definitely losing voltage elsewhere but what is considered acceptable?  Clearly losing nearly 3vdc between battery and fusible link and another .25vdc at wht/red after shunt.  Another 1.5vdc from fusible link to ignition switch.  Please advise.

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