Jump to content

jalexquijano

1972 datsun 240z ammeter not working. Easy fix or should i get a used one?

Recommended Posts

Today i fried one 15 amp fuse which is plugged in a fuse holder of the parking light harness built by dave irwin and installed in my engine. It came out melted because i removed a 15 amp i had plugged on the instrument fuse holder at the fuse box. I believe this damaged the ammeter of the car. I checked all connections and did not find anything broken. My question is: could the short damage the ammeter? My fuel gauge does work. Can this be fixed and how?

20181230_200837.jpg

Share this post


Link to post
Share on other sites

Sounds like an alternator problem to me.  Fuses pop before causing damage up stream therefore you should always use the recommended fuse.  Never go higher.

I had a bad alternator that burnt my fuse, none of gauges worked.  The internal voltage regulator went bad.  Have you upgraded the alternator?  I think after these years of using mr irwins upgrade without issue you can rule that out.

Share this post


Link to post
Share on other sites

My alternator was upgraded to 60 amp with internal voltage regulator. I dont think its damaged. Car cranks fine. Can the ammeter be fried? If so, can it be fixed?

Share this post


Link to post
Share on other sites

In the picture your ammeter shows a big current draw.  Over 45 amps.  This could be because your alternator is not charging, like site said. 

Disconnect your battery.  The ammeter should go back to the center point.  If it does it means that you have a very big current draw when the battery is connected.

  • Like 1

Share this post


Link to post
Share on other sites

I'm not positive on this but when you put a volt meter on the batteries post it should read 14.50 volts with the car running. If it's more you have a bad voltage regulator.

The gauge most likely isn't bad it's something else.  Don't get tunnel vision on the gauge.

Thanks Zed Head.  You always come up with a better answer.  We could open a shop... Sanford and Son. LOL

 

  • Haha 1

Share this post


Link to post
Share on other sites

Im tired now. Ill try that tomorrow and give you the reading. These gauges are very fragile. 46 years old

Edited by jalexquijano

Share this post


Link to post
Share on other sites
34 minutes ago, siteunseen said:

We could open a shop... Sanford and Son. LOL

Just tried to break it down to the basic question.  45 + amps is still a giant draw, over the full capacity of an early 240Z generator.  There should be smoke,or a blown fuse. if you see that on your ammeter, I think.

Could be that the needle got stuck when the fuse shorted.  Give it a tap after disconnecting the battery.  At least you'll know if the gauge is damaged or not.

Edit - on the other hand I might not know how the ammeter works.  Maybe the center point is only set with voltage present.  @SteveJ knows though.

Edited by Zed Head

Share this post


Link to post
Share on other sites
3 hours ago, Zed Head said:

  Maybe the center point is only set with voltage present.  @SteveJ knows though.

 

No, the needle sits at the center point without voltage or current.  I have one in my hand (and I'm not sitting in a Z...).

  • Like 1

Share this post


Link to post
Share on other sites
11 hours ago, siteunseen said:

put a volt meter on the batteries post it should read 14.50 volts with the car running. If it's more you have a bad voltage regulator.

 

1

and if it's less than 14.5, it"s a bad alternator.

Share this post


Link to post
Share on other sites
34 minutes ago, Mark Maras said:

and if it's less than 14.5, it"s a bad alternator.

 

11 hours ago, siteunseen said:

I'm not positive on this but when you put a volt meter on the batteries post it should read 14.50 volts with the car running. If it's more you have a bad voltage regulator.

The gauge most likely isn't bad it's something else.  Don't get tunnel vision on the gauge.

Thanks Zed Head.  You always come up with a better answer.  We could open a shop... Sanford and Son. LOL

 

Those are blanket statements and not really accurate.

  1. The ammeter is designed to indicate charge/discharge of the battery. The ammeter is situated between the battery and alternator, and most loads are on the alternator side of the ammeter. If the ammeter is on the positive side, the alternator is charging the battery and/or your brake lights/hazard lights are drawing current.
  2. Make sure you have a good battery. The specified alternator and the wiring harness are not designed to charge a dead battery.
  3. If the ammeter has failed completely, typically the car will not start since current will not flow through the ammeter. For starting the car, power goes from the battery, through the fusible link and ammeter, and to the ignition switch.
  4. If the alternator has failed, the electrical system is relying solely upon the battery, and the battery will discharge.
  5. If the voltage regulator has failed, typically the battery will reverse power the alternator when the car is off, and the battery will discharge.
  6. The FSM describes alternator and voltage regulator testing. See EE-18 for the alternator test and EE-22 for the start of the regulator testing. Of course, you can purchase a clamp DC ammeter to place over the battery cable to simplify testing. (This means you don't need to use the resistor shown in figure EE-55 if you use the clamp DC ammeter.)
  7. The voltage reading of 14.5 would be at 2500 RPM, and that is not a go/no-go voltage. A voltage between 14 and 15 VDC at 2500 RPM should be fine. As the FSM states, the alternator should show 12.5 or higher at 1000 RPM when doing the test as described in the manual.
  • Like 1

Share this post


Link to post
Share on other sites
14 hours ago, siteunseen said:

I'm not positive on this but when you put a volt meter on the batteries post it should read 14.50 volts with the car running. If it's more you have a bad voltage regulator.

The gauge most likely isn't bad it's something else.  Don't get tunnel vision on the gauge.

Thanks Zed Head.  You always come up with a better answer.  We could open a shop... Sanford and Son. LOL

 

Readings taken both at positive of alternator and at battery with car at idle. Ammeter still at zero. I have a spare one and already verified that my connectios were tight on the one installed.

20181231_121031.jpg

20181231_120940.jpg

20181231_121108.jpg

20181231_115352.jpg

Share this post


Link to post
Share on other sites
10 hours ago, cgsheen1 said:

 

No, the needle sits at the center point without voltage or current.  I have one in my hand (and I'm not sitting in a Z...).

Just reading what others have said I don't think your gauge is the problem.

From Steve's post...

If the ammeter has failed completely, typically the car will not start since current will not flow through the ammeter. For starting the car, power goes from the battery, through the fusible link and ammeter, and to the ignition switch.

And that's the starter not the alternator you're checking voltage on.  I'm sorry I can't be more helpful.  Good luck.

Where does the needle point when the car is off?  Should be at the center.  Then when the car is running does it go all the way to the left, negative?  If it stays at the left running or not, I would disconnect the battery and see where the needle goes.  Again, good luck.

Edited by siteunseen

Share this post


Link to post
Share on other sites
5 minutes ago, siteunseen said:

Just reading what others have said I don't think your gauge is the problem.

From Steve's post...

If the ammeter has failed completely, typically the car will not start since current will not flow through the ammeter. For starting the car, power goes from the battery, through the fusible link and ammeter, and to the ignition switch.

And that's the starter not the alternator you're checking voltage on.  I'm sorry I can't be more helpful.  Good luck.

Where does the needle point when the car is off?  Should be at the center.  Then when the car is running does it go all the way to the left, negative?  If it stays at the left running or not, I would disconnect the battery and see where the needle goes.  Again, good luck.

Negative battery pole disconnected, tap given with closed fist to the gauge, needle went tobñ center and viola ammeter working again. Thanks to all of you for your great help throughout these 4 years and exhaustive patience. Happy new year! 

20181231_123017.jpg

20181231_123400.jpg

  • Like 2

Share this post


Link to post
Share on other sites
28 minutes ago, siteunseen said:

Just reading what others have said I don't think your gauge is the problem.

From Steve's post...

If the ammeter has failed completely, typically the car will not start since current will not flow through the ammeter. For starting the car, power goes from the battery, through the fusible link and ammeter, and to the ignition switch.

And that's the starter not the alternator you're checking voltage on.  I'm sorry I can't be more helpful.  Good luck.

Where does the needle point when the car is off?  Should be at the center.  Then when the car is running does it go all the way to the left, negative?  If it stays at the left running or not, I would disconnect the battery and see where the needle goes.  Again, good luck.

Sorry for the misrepresentation of the part. Anyway problem fixed. Thanks to all of you. By the way i wish my air conditioner would blow more cold air. The gen ii mini evaporator need more flow.

Share this post


Link to post
Share on other sites

@jalexquijano Happy New Year Buddy. Glad you coerced the gauge back into working condition again. A word of caution. The problem will reoccur and too many thumps on the plastic faceplate will eventually crack it. V.O.E. Don't want to hijack the thread but how's your Z running these days?

Share this post


Link to post
Share on other sites

Im reading a book that describes the development and problems this car faced regarding vapor lock. Havent taken the car out for spin during stop and go traffic jams on week days. I was thinking that my 1972 240z could also have the symptoms described. 

20181231_142019.jpg

20181231_142132.jpg

20181231_142112.jpg

Edited by jalexquijano

Share this post


Link to post
Share on other sites
3 hours ago, Mark Maras said:

@jalexquijano Happy New Year Buddy. Glad you coerced the gauge back into working condition again. A word of caution. The problem will reoccur and too many thumps on the plastic faceplate will eventually crack it. V.O.E. Don't want to hijack the thread but how's your Z running these days?

When I bought my '77 the face of the oil gauge was up against the needle.  The guy I bought it from thought the gauge was bad I reckon?  He tapped it out of the holding ring.  I doubled up some duct tape and pulled it back into place then rebuilt the motor with a turbo oil pump. LOL

  • Like 1

Share this post


Link to post
Share on other sites

WHere can i purchase a 24" high quality negative battery cable with a soldered terminal and additional 4 inch cable which will be fastened to the firewall?  Maybe something similar. I would prefer the original negative battery cable for my 1972 240z.

https://www.autozone.com/batteries-starting-and-charging/battery-cable/duralast-battery-cable/570458_310040_0

Please advise if it the original negative battery cable was  24 inch long?

 

 

 

Share this post


Link to post
Share on other sites

rockauto.com has a lot of information and part numbers for '72 240Z battery cables. There is a difference from 6/72 to 7/72 also manual or automatic. Not sure what it is.

Happy researching.

Share this post


Link to post
Share on other sites
19 hours ago, siteunseen said:

rockauto.com has a lot of information and part numbers for '72 240Z battery cables. There is a difference from 6/72 to 7/72 also manual or automatic. Not sure what it is.

Happy researching.

Mine is  1/72

On 12/31/2018 at 12:34 PM, siteunseen said:

Just reading what others have said I don't think your gauge is the problem.

From Steve's post...

If the ammeter has failed completely, typically the car will not start since current will not flow through the ammeter. For starting the car, power goes from the battery, through the fusible link and ammeter, and to the ignition switch.

And that's the starter not the alternator you're checking voltage on.  I'm sorry I can't be more helpful.  Good luck.

Where does the needle point when the car is off?  Should be at the center.  Then when the car is running does it go all the way to the left, negative?  If it stays at the left running or not, I would disconnect the battery and see where the needle goes.  Again, good luck.

Negative battery pole disconnected, tap given with closed fist to the gauge, needle went tobñ center and viola ammeter working again. Thanks to all of you for your great help throughout these 4 years and exhaustive patience. Happy new year! 

  • Like 2

Share this post


Link to post
Share on other sites

All the Z specialty shops should have one. You found autozone.com I said rockauto.com then there's always amazon.com. 

Measure your old one and I'll measure mine. Report back with results.

 

 

Share this post


Link to post
Share on other sites

24 inches is plenty. You can tuck and hide the extra wire. Mine have been replaced too. I see now I have room to go to an opposite post battery. Get the hot out from under the fender.

20190205_162339.jpg

 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Recently Browsing   0 members

    No registered users viewing this page.

  • Who's Online   14 Members, 0 Anonymous, 73 Guests (See full list)

  • Search Engine Meta Tags:
    classic, z, datsun, 240z, 260z, 280z, zcar, zed, s30, classiczcars.com, 240z.org, fairlady, 240, 260, 280, nissan, 240 z, 260 z, 280 z, zx, turbo, classic z, 280z cars, cars 240z, car forums, datsun, nissan, cars datsun, car club, 280zx, car, nissan zcar, classic z car,performance,300zx, car years, car raced, texas 350z, 300z, 350z, nissan racing , clubs car, zcca, club datsun
×

Important Information

By using this site, you agree to our Terms of Use. We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.