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    1. · Registered
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      pictures... of the alternator from several angles so we might be able to identify it and see which wiring..

      and a huge warning..

      i have only been a mechanic for 35 years.. and i do a ton of electrical work on cars ..

      if you have a battery cut off switch... its designed to CUT off the battery.. NOT kill the motor ..

      if the battery disconnect switch is turned off... while the engine is running. there is a chance of serious damage to the alternator components..

      when the battery cut off switch contacts are disconnected.. there is a huge loss of load on the alternator output. the alternator was creating electrons at 14.6 volts or so.. the instant the switch is opened.. the electrons being created in the alternator build up as there is no place for them to go.. the build up becomes a voltage spike as the regulator takes a few hundredths of a second to turn off the power to the rotor windings. its really easy if the alternator is putting out any were above 30% of rated output at the time the switch was opened for the voltage spike to go over 100 volts for that split second..

      diodes in many alternator are rated at 25 or 35 amps 100 Volts PIV.. peak inverse volts.. if you exceed the voltage you can fry the diodes. causing them to blow out and open.. or what is worse... is when they short out.. they will flow current in both directions... a diode is a one way check valve..

      perhaps this is what you are finding..

      do you own a hand held digital volt meter.. this is a link to a voltage drop test i use to verify the electrical connections are working properly.. print this.. it will not only help find issues on hot rods but on everyday drivers including the latest computerized cars..

      voltage drop test link.. http://i.imgur.com/WMDprhm.jpg

      since you have a rear mounted battery.. you will need a probably a jumper cable laid on the floor under the car to extend the reach of the volt meter test leads..
      this is the meter i use to perform these tests.. Digital Multimeter - Save on this AC/DC Digital Multimeter the really cheep under 10 buck meters may not be accurate at these tiny fractions of a volt you are checking for.. i know that as i have tried them..


      let me walk you thru the tests....

      engine off.. turn on the headlights for one minute .. then shut them off and check the voltage ... if the battery voltage is less than 12.50. volts.. then you need to recharge the battery slightly.. the reduced charge will throw the test results off ... you can still do the six steps.

      start the engine.. turn on the headlights to create a mid sized load on the electrical system.

      test 1... should be over 14.1. and usually less than 14.8 volts.. if the alternator is not putting out current above the battery voltage the test results will be off..

      test 2 requires with rear mounted battery that you hook up the single jumper cable to the negative battery post.. so you can connect the one of the volt meter test leads to the other end... touch the engine block.. i would love to see 0.04 volts.. please post results.. by number... this checks the engine blocks negative connection to the battery.. 0.04 is 4/100ths of a volt.

      test 3 also requires the use of the single jumper cable or just connecting between the negative battery post and the body.. less than 0.02 volts would be a great result.. this checks the negative connection to the body.. since all the lights and many other devices are connected to the negative thru the body this is an important test.. 0.02 volts is 2/100ths of a volt..

      test 4 can be done up front.. engine block to the firewall . or body... 0.02 volts again is a good result. why.. the alternator puts out almost 2 volts more than the battery.. with most of the electrical devices grounded to the body.. failure to have usually a braided ground strap from the engine to the firewall or body will really effect how the electrical system works.. as much of the load is on the alternator with the engine running. electrons like to take the shortest path..

      test 5 is hard to do on some cars.. its designed for cars with underhood fuse boxes... if your car is equipped with a terminal block where the wiring from the alternator or from the positive battery connection supplies the rest of the electrical system with positive power this is the test to perform.

      test 6 is really important.. with a rear mounted battery.. you will really want to be careful.. as i am going to have you use the single jumper cable laying on the floor under the car and clamping the end to the positive battery terminal.. clip one lead of the volt meter to the clamp on the floor.. do not let the jumper cable touch the car.. hopefully your test leads are long enough to do this.. and touch the other test lead to the alternator output.. this reading is going to be in most cases... around 0.3 volts. less is better. some cars like 60s and 70s mopars will have 0.7 volts as the length of the wire between the alternator and the battery positive is really crazy long.

      on a conventional car.. i can perform the first 4 steps in under a minute to check the negative side connections..

      testing the positive side is not always possible.. as some cars you cannot get to the back of the alternator to touch the threaded stud.. not the ring terminal in most cases..

      why are these small fractions of a volt a good result..

      if you have a poor electrical connection.. this test may find it.. its just the beginning test and actually the last test i perform on any car before i close the hood to verify that the electrical system is properly hooked up.. i hate comebacks..

      the 4/100 or 2/100 of a volt results is the actual resistance of the copper wire to electron flow.. if your tests show more... you will want to narrow the test locations .. to identify the poor connection..

      if you have a daily driver that has an underhood fuse box.. most cars 1994 and up have them.. spend a few minutes with your digital volt meter and the paper copies of the voltage drop i posted above and perform it so you can see what the results may be..

      you said the car has a short... this is the first step in any proper electrical diagnosis..

      try to post results by number..
      percentage of battery charge 12.65/12.45/12.25

      1....______

      2....______

      3....______

      4....______

      5....______

      6....______


      lastly.. with a battery cut off switch.. you will want to perform a voltage drop test from both of the threaded studs individually to the negative battery post.. this is done engine running and the headlights on..

      this does not explain why the alternator seems to be drawing current with the engine off.. but you have not described the type of charging system.

      sorry for the wall of text.. just trying to help.. use the printed voltage drop test.. at the car.. most of this was explaining the need to modify the procedures for checking with rear mounted battery..
       
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      Thanks for all the awesome info! We had to do the hearse shuffle today and then move a bunch of the landord's cars, and that basically took all day. The only thing I managed to do was check the sensor itself (yes I found it lol). Looks like the sensor itself is good. So my next step would be to test the other things you mentioned. Although I am thinking that I am just going to take the whole cluster out. I have another cluster, but I am not sure if I want to use it. The plastic cover on the cluster is smashed to pieces on the one thats on her and I do also have the plastic piece to replace that but regardless I have to take the thing out.

      It was really nice to have all the kids out today, even just for a few minutes. I've really gotten over my heard though. They all need so much work.. But I wont give up. The 66 is my project car and now she's out in the open ready to be worked on. I think I'm just going to send the other cars to professionals, or else this stuff is never going to get done.

      The 71 today didnt make that parking pawl noise, but he spewed oil into the street. It's coming from somewhere near the starter it looks like, but I'll make a different post about that. Poor thing lol..

      Come to think of it, maybe I just blew a fuse? Although if that's the case, my worry is why that might be.I don't have a straight up Ohmmeter, just a DVOM and it only has one Ohm setting, but the placement is automatic. Unfortunately I wasnt able to test anything today that involved turning the key on, as she currently has no battery in her. That's next lol... This car at one time was my daily driver. I've kind of let her go a little because I suddenly had 3 hearses to care for, and now I have 4. If only money grew on trees...
      far superior cheep volt meter.. Digital Multimeter - Save on this AC/DC Digital Multimeter

      there are several versions of this test light.. 6/12V Circuit Tester with 5 ft. Lead warning. the wires sometimes break off them. but are easily soldered back on.

      these are standard diagnostic tools.. that without them it makes it hard to do most things on cars..

      if you have cars that use ignition POINTS.. and you don't have a dwell meter... invest in this one instead of the 37772. LCD Automotive Multimeter with Tachometer Kit

      if you have a spare dashboard.. i would keep it around... and check the fuses and power to the fuse first.. its a lot of stuff swapping the dashboard.. these are all individually wired bulbs in holes in the dash... and there are tons of vacuum hoses back there to contend with on 65 and 66 models.
       
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      sorry i forgot to explain..

      when you first turn on the key to the RUN position.. newer OBD2 models handle this before the RUN position.. but i can explain that later..

      so the key turns on.. the ECM sends power to the green and white tire for 2 seconds to prime the fuel system.. when you start to crank the engine. the computer sees the voltage on the CRANK circuit to the ECM and will power up the fuel pump relay again... it will also look at RPM pulses from the ignition distributor..

      when the engine starts.. and you release the key.. if the computer sees pulses from the distributor. it will keep the fuel pump relay powered up.. (varies upon year and model)

      now that the engine is running the oil pressure switch diaphragm will flex up and close the contacts connecting the orange 440 circuit to the fuel pump wiring.

      i have a crazy neat test to check the oil pressure switch contacts...

      with the engine idling.. i unplug the fuel pump relay.. if the engine dies. then the oil pressure switch is bad or the wiring to it is bad..

      up thru 2003 on GM trucks.. GM used both fuel pump relays and oil pressure switches. . above 2003.. its mostly fuel pump relay only.

      oil pressure switches...

      3 prong oil pressure switches.. the outer 2 contacts are usually for the fuel pump relay parallel power circuit..

      some earlier GM versions used 2 oil pressure switches.. usually a single terminal version and a twin terminal version.. the single terminal was for the gauge in the dashboard. the 2 terminal version was for the fuel pump relay.. some models with carbs used the 2 terminal versions to supply power to the electric choke coil. in a very creative circuit much like the alternator light circuit..

      another test to go with the one above .. .i pull the fuel pump relay... i remove the cover from it.. i plug the bare relay back in.. i then squeeze the bare relay and listen to the fuel surge thru the fuel lines.. sometimes i monitor the amp draw with one of these..

      30 Amp Automotive Fuse Circuit Tester
      they used to have a 20 amp version that worked with the smaller fuses..

      i use these as they have a 20 amp DC setting.. Digital Multimeter - Save on this AC/DC Digital Multimeter and when it breaks.. i toss it in a pile to save for parts for the next one.. i am on my second in 10 years.. and i abuse them.

      oh great.. you are overseas.. i forgot.
       
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      thanks all for the info. I will start figuring this out over the weekend. Probably remove taillight bulbs or disconnect wiring to the bulbs first since its easier, but I also believe its behind the gauges, Its just major hassle to remove the cluster with a CD player located below it, but at least then I might see any grounding issues with the needles jumping.

      In the past I've always built my own cars (first car a T bucket in 1971) so I knew where every nut and bolt and wire was. Purchased this one about 4yr ago that was built about 15yr ago, and while it was professional built, its still sorta like an easter egg hunt to figure things out on her.
      Let me help you with your easter egg hunt...

      to narrow down which circuit is causing the issue.. i took your picture and folded it in my mind.. added what is probably the proper circuit names..

      you will want to photograph the connector from the top. .. then unplug it..

      do you know how to depin the series 56 connectors used.. by pushing the wire and terminal inwards slightly while depressing the latching tab on the flat side of the terminal then pulling it out..

      i attached my modification of your image..

      the red wire at the top of your picture i labeled Tailight power into switch is probably the fused power circuit that blows.. but that is not the cause..

      do you see the White wire i labeled instrument cluster. that probably goes to the instrument cluster.. in many OEM wiring setups.. that does not feed the cluster directly that feeds a 3 or 5 amp cluster fuse in the fuse box. then up to the cluster.. this prevents a dashboard short from taking out your tail and parking lights.

      there are 3 wires above the white wire.. a dark blue i labeled tail or front parking..

      and a pair of tan wires into one terminal.. also labeled tail or front parking.

      its going to be one of these circuits that is causing your tail light fuse to burn out..

      if you don't have a hand held digital volt meter... you may want one of these.. Digital Multimeter - Save on this AC/DC Digital Multimeter

      you will want a pair of these also. 36 in. Low Voltage Test Leads so you can connect your test probes to ground without having to hold them. frees up at least one hand.

      you can set it to 200 Ohms scale and measure each of the wires directly to ground.. this will tell you which one has the dead short..

      post the results by wire color..


      white...

      blue..

      tan pair..

      the tail light filaments in 1157 bulbs are around 2.0 ohms ..
      the Brake and turn filaments are around 0.5 ohms..

      since you are working with the tail light circuit.. you are going to be working with the 2 ohms... now.. my brain does not work well in math.. with multiple 2.0 ohm bulbs in the circuit.. will there be only 2 ohms or will there be less.. they are in parallel.. so i would expect only 2 ohms.. this would be on the TAN pair of wires or the dark blue wire..


      since i don't know what bulbs are used in your instrument cluster backlighting circuit.. i don't know what kind of resistance you are going to get and i don't have a single 194 or 168 bulb near me this morning to measure. expect over 2.0 ohms. on the white wire to ground.. if you have less.. you may have a short on that circuit..

      please print this text so you can follow it under the dashboard..
       

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      is it the dimmer switch?? failing.. autozone headlight switches are wells ve brand.. a supplier to auto manufacturers.. i have opened the duralast switches and found OEM versions in the boxes. since they have a decent warranty.. i don't fear using them.

      if you have an HF around.. http://www.harborfreight.com/ac-dc-digital-multimeter-37772.html this has a 20 amp DC setting.. i use it all the time.. here i am testing a TBI fuel pump for amp draw.. https://youtu.be/vEiZ5QRu9Mw i do use several sets of test leads... this is the one i use 90 percent of the time.. http://i.imgur.com/5nWxSkY.jpg i assembled from components.

      here.. have something else to enjoy for a few minutes.

      SR-71 Blackbird pilots trolls arrogant F-18 pilot - Album on Imgur
       
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      http://www.askatech.com/askatechlive/aatfileshare/references/fasttrack/g005.pdf

      the above file describes on the last page how to test the sensor ground.


      your truck would be the A201 or A204 file.. and that is not linked.. might still work.. i used to have those files in a PC code .. i am a mac user.. but that USB scan tool set up might work if you have a PC laptop.. i did see a guy tuning with a full tower computer and 19 inch monitor strapped into the front seat of his 69 camaro one day.. i guess he did not realize he could jack up the rear wheels.. but that is off subject..

      you might want to breeze thru this post offsite..

      which used scan tools for 82 to 94 corvettes with OBD1 connectors.. Page1 - Corvette Forums at Super Chevy Magazine

      since you don't have a volt meter.. buy one of these.. its the same one i use daily.. Digital Multimeter - Save on this AC/DC Digital Multimeter


      you will want the fuel and emissions manual.. either printed or DVD..

      Search

      if you have a 1993.


      you will also want to use this to gain some knowledge of the TBI system

      http://www.gmceast.com/technical/Swartzendruber_Generic_TBI_SlidesNotes.pdf

      i have some more stuff.. but without you owning a digital volt meter... you won't have any luck even if you used a baseball bad..

      are you in the los angeles area.. where i could just come over and plug in a scan tool.
       
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      Discussion Starter · #12 ·
      http://www.askatech.com/askatechlive/aatfileshare/references/fasttrack/g005.pdf

      the above file describes on the last page how to test the sensor ground.


      your truck would be the A201 or A204 file.. and that is not linked.. might still work.. i used to have those files in a PC code .. i am a mac user.. but that USB scan tool set up might work if you have a PC laptop.. i did see a guy tuning with a full tower computer and 19 inch monitor strapped into the front seat of his 69 camaro one day.. i guess he did not realize he could jack up the rear wheels.. but that is off subject..

      you might want to breeze thru this post offsite..

      which used scan tools for 82 to 94 corvettes with OBD1 connectors.. Page1 - Corvette Forums at Super Chevy Magazine

      since you don't have a volt meter.. buy one of these.. its the same one i use daily.. Digital Multimeter - Save on this AC/DC Digital Multimeter


      you will want the fuel and emissions manual.. either printed or DVD..

      Search

      if you have a 1993.


      you will also want to use this to gain some knowledge of the TBI system

      http://www.gmceast.com/technical/Swartzendruber_Generic_TBI_SlidesNotes.pdf

      i have some more stuff.. but without you owning a digital volt meter... you won't have any luck even if you used a baseball bad..

      are you in the los angeles area.. where i could just come over and plug in a scan tool.
      No I live in Mississippi and thanks for the links I will look into them
       
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