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How to check ignition wire voltage


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Does anyone know how to check the ignition wire voltage on both sides of the bulkhead connector in my 1967 Buick Skylark?  The resistor wire is burning hot and it's not letting the alternator charge the battery like it should.  I have a new alternator, but it won't charge the battery, it only gets 12.5 volts when its running but it should like 13.9 or 14.2.  I believe that the problem is the ignition wire and after I do check it, how many volts should it be? Thanks.

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Sounds like there might be some other wiring issues in the mix?  When the bulkhead connectors are assembled at the factory, I believe they might put some sort of non-corrosive coating in them, or possibly a thin coat of spray undercoat on the seam where the outer connector slides into its "mate".  End result is that the inner terminals can become "gunked" with age and can resultantly have higher resistance than they should.  So, in your investigations, you might consider taking the outer bulkhead connectors apart and seeing how clean they might be internally, repairing as necessary.


You might also get a GM Underhood wiring schematic and trace the wiring to see if any changes have happened.  It will need to be model year and model specific AND from GM.  If there's a resistance wire that's getting current when the ignition key is "on", it probably will have some heat in it . . . as the resistance wire that feeds the ignition points (in concept, the same as a ceramic ballast resistor), for example.  Only other resistance wire I can think of is the fusible link wire going to the starter.


Alternator output voltage should be, when the engine is running, in the 14 volt range you mentioned.  I don't recall any "resistance" wire being in the alternator circuit, just for the reasons you mentioned.  Still though, it's "amps" that charges the battery, with the result being "volts". 


First, I'd check the wiring circuits against the factory GM schematic. Color codes and where they all go from and to in the wiring harness.  Plus checking the bulkhead connector terminals for resistance/continuity with a digital volt/ohm meter.


If all of that checks out (and/or are repaired as needed), then I'd get a shop to do a Charging System Check to see how well the alternator is performing itself.


Of course, the battery will NOT charge is there is corrosion on the battery cable terminals AT the battery!  I had on deal where I put an electronic ignition upgrade on a vehicle.  In checking it, I restarted it several times, but on the 5th consecutive time, nothing happened.  It was getting "volts" everywhere, but "no starter engagement".  I finally discovered a thin coating of "gunk" between the inner surface of the cable terminals and the battery post terminals.  Kind of hidden and looked to be minor, but cleaning both the terminals with a wire brush terminal cleaner fixed that issue.  On newer vehicles, I've seen alternator output be 10% less than spec due to battery terminal "coatings" on side post battery terminals.


Also, check the batter cables for voltage loss between the battery and engine parts/chassis ground areas.  What you're looking for is internal resistance/continuity issues, which would be hidden under the cable's outer insulation sheath.  Check both with the engine running and stopped for similar results.


And, of course, where those cables attach need to have clean surfaces also.  As a general principle, check any chassis ground straps for the engine/chassis to ensure they are there and in good condition. 


Everything's one big circuit and all attachments need to be working well, else "the juice" will seek to find the easiest "ground" and go there to complete its circuit.  In some cases (as signal light bulbs which have failed), it can result in "back-feeds" that make some unusual things happen.  I don't really suspect that's what's happening in your alternator case, but something to be aware of.


Holler back or send me a Private Message if you might desire.


Keep us posted on your progress, please.



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