Battery voltage

BlksvtCobra01

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Mine does the same thing. I thought I was having a problem so I replaced the alternator and battery. After all that, same thing. I wasted money.

I'll check my grounds.

Good to know. I have no battery light at WOT. When I start it cold it normally is around 14.0-14.2 after driving 13.5 sometimes after the heat 13.2. When I had the AC on max Memorial Day 12.8 at times to 13.2. When I turned the AC off 13.3-13.4 lowest 13.2.


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94 Cobra R

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have the big 3 upgrade on mine with J2 alternator. My pid still reads about .5 difference. I have a voltmeter gauge in place of the cig lighter in the shifter bezel and it matches at the battery perfect (reading off of the harness that a convertible switch would be hooked up to.


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94 Cobra R

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DSG2003Mach1

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View attachment 1642914


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does that plug into the cig lighter or you remove it and wire it up in its place?

I looked at my car tonight, looks like theres 3 small ground wires at the radiator support. A short one to the battery neg terminal, its in a dual terminal with another ground that runs off into a harness. There is a separate ground that also runs off into a harness between battery and fender. It sounds like he basically removed the tiny wire from rad support to neg terminal and put in a bigger wire with its own eyelet and reattached with the same ground screw to keep those 2 wires together
 

Stage 4.6

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Definitely checking mine this weekend, Ive been extremely nervous with the dropping of voltage ever since i had my Fore fuel system installed. I hear a lot of people discussing how the voltage drop on the pumps can be disastrous.
 

HPLouis

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Good to know. I have no battery light at WOT. When I start it cold it normally is around 14.0-14.2 after driving 13.5 sometimes after the heat 13.2. When I had the AC on max Memorial Day 12.8 at times to 13.2. When I turned the AC off 13.3-13.4 lowest 13.2.


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Exactly like mine on both my 2700 mile convertible (when I had it) and my 14,000 coupe.

Same exact behavior.


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BMSTNG

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Good to know. I have no battery light at WOT. When I start it cold it normally is around 14.0-14.2 after driving 13.5 sometimes after the heat 13.2. When I had the AC on max Memorial Day 12.8 at times to 13.2. When I turned the AC off 13.3-13.4 lowest 13.2.


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Same numbers I get also on my 7,400 mile coupe, with the original alternator. Seems like the norm
 

BOOGIE MAN

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@94 Cobra R Love that baseball shifter boot

Posts are mine and do not represent my employer. Actually, my posts are riddled with humor and sarcasm and are not to be taken as a representation of my thoughts, feelings, or ideas. Same goes for my "likes"
 

brownsvo

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Upgrade the wires, clean your grounds, and dont waste money on a stock alternator.
Or PA
Or Ebay.

Fashion a vent using the bumper and dryer hose if you live someplace hot.
 

*Jay*

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When I've had the issue of the volts dropping as things warmed up it was the alternator. The ground might be getting finicky if its corroded inside. But mine did it with an upgraded ground as well. I went with the J2 Fab when it was on sale.

You can make your own ground cables with some eyelets and spare battery cables. I had some extra wire laying around from stereo installs and used that.

I had the exact same issue with the stock alternator my Cobra came with, a stock unit I had rebuilt and with a supposedly new OEM unit from Rockauto. Upgrading the wiring (repairing actually) was one of the first things I did when I started having voltage issues with my Cobra, it was a mess to say the least but wasnt my only problem. The first 2 alternators started being affected by heat over the course of a few years, the new OEM from rockauto was affected by heat from the day I installed it. I installed a Mechman and havent had any heat issues since.

Now lets talk about the voltage readings. The voltage read at the battery will always be different than voltage being read somewhere else down the line. There is always going to be voltage loss through a wire, while the loss through a single length of wire is minimal it is cumulative. The more length in wiring, the more connection points, any loose connections, every crimp, bad repairs, any corrosion, any damaged wiring, environmental conditions and more all contribute to voltage losses. Keep in mind this applies to both Positive and Negative wiring. The negative path in a circuit back to the battery may not be as direct as the positive but it is still just as important.

This is why that small ground lead from the Negative terminal to the radiator cowl helped hotcobra03 and others, that was the weak point in the path back to ground that their ECU was using when reading their operating voltage. There are ground points all over the car and in theory they "should" read the same. Think about what the path of least resistance is when you go to read the voltage going to your tail lights and use a random bolt in the trunk for your negative meter lead. Thats why whenever someone starts having voltage issues the first thing I tell them is to look at all their wiring especially the grounds between various locations.
 

Fastback

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In my experience, ground corrosion or loose grounds, account for 3/4 of electrical problems! Hate electrical!
 

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