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  •  » Electrical Anomaly

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    8/20/2020 2:09 PM  #1

    riwall
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    From: Sherman, Texas
    Registered: 4/02/2013
    Posts: 208

    Electrical Anomaly

    I will admit that my electrical expertise begins and ends at the on/off switch. Anyway, I am still having issues with my '67 Mustang 302. It began a couple of months ago. After driving it for perhaps 10-15 minutes and turning it off, the engine turns over very slow when trying to start it but generally does start. So, here is what I've done:
    - Had the battery checked. NAPA said the battery was OK but needed charging which they did.
    - Had the alternator checked and was told it is good.
    - Got a new alternator wiring harness because the old one was brittle and ratty.
    - Installed a new voltage regulator.
    So, today I began with a fully charged battery, hooked up a voltage meter and the battery showed 12.4 volts. I started the engine and the voltage jumped to about 14 volts and stayed there. I turned on the A/C and the voltage dropped to about 12 volts. Is that normal? After turning off the engine I checked the battery again and it was at about 11.8 volts. 
    Any suggestions as to what to do next? Thanks for any help.  

     

    8/20/2020 2:46 PM  #2

    bearcat
    I FYI 24-7

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    From: Twin falls, Idaho
    Registered: 4/01/2013
    Posts: 337

    Re: Electrical Anomaly

    check your grounds, you are not getting the voltage to the battery and hence to the rest of the car. why I say check your grounds. Then with the car running what is the voltage at the battery, then check and see what is the voltage coming from the alt.( are you running a stock alt?) these can be checked with a multi meter. sound like a bad ground or power cable. 

    65 coupe, 351w, c4, power disk brakes, power r&p, vintage air.
     

    8/20/2020 2:52 PM  #3

    Ron68
    Senior 24-7 FYI Addict

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    From: Mukilteo, Washington
    Registered: 4/01/2013
    Posts: 1,400

    Re: Electrical Anomaly

    To keep that battery charged, the alternator output should be 13.8 to 14.5 vdc. If it drops to 12 vdc under load with the  AC compressor clutch engaged what does it look like with headlights, heater blower motor and wipers on? What is your engine idle speed? Is it high enough to keep the battery charging under a normal electrical load? What is the actual capacity of your battery? Did NAPA do a load test on it? How old is the battery?

    68 coupe - 351W, 4R70W, 9" 3.25 -- 65 convertible - 289 4v, C4, 8" 3.00
     

    8/20/2020 4:48 PM  #4

    Bolted to Floor
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    From: Houston, Texas
    Registered: 4/01/2013
    Posts: 1,918

    Re: Electrical Anomaly

    Agree with checking the grounds.

    How are your cables (condition, appearance) from the battery to solenoid and solenoid to starter? Do they get warm when it’s cranking slow? I think the under hood heat and a cable going bad could cause what your seeing. What size are the cables? The bigger the better as long as the wire insulation is rated for the heat.

    Last edited by Bolted to Floor (8/20/2020 4:49 PM)

    John  -- 67 Mustang Coupe 390 5 speed
     

    8/20/2020 5:22 PM  #5

    HudginJ3
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    From: Cedar Hill, TX
    Registered: 4/29/2015
    Posts: 1,218

    Re: Electrical Anomaly

    Any connections, positive or ground, that are loose, dirty, or warm/hot will leak electricity. Your stock system will not charge the battery very good with the engine at idle and the A/C on. Your check with nothing on is a normal condition. With every electrical gadget you have turned on and idling will result in less than 12v, coming from the alternator and that is normal as well. Notice your battery charge/voltage while cranking your engine. 9v or less is not enough to start the car. Battery voltage going down to close to 9v is normal while cranking.

    70, ragtop 351W/416 stroker Edel Performer heads w pro flow 4, Comp roller 35-421-8. T5
     

    8/20/2020 6:20 PM  #6

    riwall
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    From: Sherman, Texas
    Registered: 4/02/2013
    Posts: 208

    Re: Electrical Anomaly

    Wow. Lots to consider. The cables (battery/starter/ground) are in good shape and good quality, replaced less than 2 years ago. The alternator is grounded to the block and the firewall so that should be ok. Not sure what other grounds I need to look at. I don't think that NAPA did a load test on the battery so I'll get that done tomorrow morning. The battery is 2 years old. The idle RPM is 900. 
    Thanks for the help. 

       •Thread Starter
     

    8/20/2020 7:38 PM  #7

    MS
    Forum Originator

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    From: Canyon Lake, Texas
    Registered: 1/24/2013
    Posts: 11,729

    Re: Electrical Anomaly

    Retard the timing two degrees and see what the effect is.

    Money you enjoy wasting is NOT wasted money... unless your wife finds out.
     

    8/20/2020 7:45 PM  #8

    riwall
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    From: Sherman, Texas
    Registered: 4/02/2013
    Posts: 208

    Re: Electrical Anomaly

    Hmmm. Interesting. Thanx Steve.

       •Thread Starter
     

    8/21/2020 10:21 AM  #9

    Kristang
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    From: Minneapolis, Mn
    Registered: 4/01/2013
    Posts: 293

    Re: Electrical Anomaly

    I had a slow hot start issue in my car.  Everything is brand new.  I added a dedicated ground from the starter to the frame and problem was solved.  I also made sure my grounds were contacting bare metal and not over any paint.  I have had such an adventure with electrical items in this car! LOL  Crossed fingers, I think they have all been resolved!  Now I am going to list this car for sale on move on to my newly acquired 65 Fastback!
     

     

    8/21/2020 11:00 AM  #10

    riwall
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    From: Sherman, Texas
    Registered: 4/02/2013
    Posts: 208

    Re: Electrical Anomaly

    It looks like the problem may have been the battery. I took it to NAPA twice and both times they said the battery was OK and just needed a charge. I don't think they did a load test on it so I took it to another shop and had that done. It failed. The battery was only 2 years old so I got a bit of a break on the warranty. Everything seems to be fine now but the jury is still out on whether this was the only issue. Time will tell. 

       •Thread Starter
     

    8/21/2020 2:36 PM  #11

    bearcat
    I FYI 24-7

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    From: Twin falls, Idaho
    Registered: 4/01/2013
    Posts: 337

    Re: Electrical Anomaly

    Glad to hear you got it figured out. 

    65 coupe, 351w, c4, power disk brakes, power r&p, vintage air.
     

    9/02/2020 11:37 AM  #12

    riwall
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    From: Sherman, Texas
    Registered: 4/02/2013
    Posts: 208

    Re: Electrical Anomaly

    Well, the battery may have been weak but it was not the problem. After a 20 minute drive and parking it at home I tried to re-start and it hardly turned over so obviously the alternator was not charging the (new) battery. I did what I should have done at the outset - I bought a new 1 wire 100 amp alternator. I installed it this morning. The battery voltage was about 12.3. When I started the engine the voltage jumped to about 14.2. I turned on the A/C and radio and the voltage stayed at about 14. It has been a frustrating learning experience but I'm back in business - until the next crisis.

       •Thread Starter
     

    9/02/2020 12:06 PM  #13

    bearcat
    I FYI 24-7

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    From: Twin falls, Idaho
    Registered: 4/01/2013
    Posts: 337

    Re: Electrical Anomaly

    Its always a learning curve with these old cars. we are always chasing something 

    65 coupe, 351w, c4, power disk brakes, power r&p, vintage air.
     

    9/02/2020 1:02 PM  #14

    Rudi
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    From: Stuck in the 50's Welland Ca
    Registered: 4/01/2013
    Posts: 3,783

    Re: Electrical Anomaly

    Many battery web sites say that the vehicles alternator is not meant to bring a battery up to full charge, that’s the job of a dedicated  battery charger, preferably one that has a conditioner function.
    Inexpensive trickle  chargers are not recommended to bring a battery up to the proper operating voltage, they say some do more harm than good.
    I use a CTEC charger that has AGM, diagnostic and recon functions that I put on if not driving the car for a week or so.

    Good work ain't cheap, Cheap work ain't good!   Simple Man
     

     

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