Voltage drop

[Carrnutt]

Ok, I have a problem with losing voltage across the car. when i turn the key on, I lose almost a full volt, down to 11.5. then when i use turn signal, brake, hazards etc, my light even just the dome light will dim in rhythm. the voltage drops another volt, in the end i drop to 9.8 volts at the fusebox, sadly not enough to keep the radio on. I've checked everything, thinking maybe just resistance in the wires? checked the ign swith, the alt, new batt and everything i can think of. the car is wired for electronic ign and volt reg. Oh and while I'm here, picking brains, how can i adjust if possible and after market sending unit for the fuel gauge, ive already tested it and it pegs full when grounded, reads the 1/2 full thing.  thanks in advance

[elacruze]

You know what a voltage drop is, that's a good start. Now you just need to perform that test across every electrical joint between your fuse box and the battery positive terminal.

Search the archives, you'll find thread or threads on the positive feed coming through the firewall plug, that sounds like a likely spot for trouble.

Try to be more descriptive in your explanations, where have you done the voltage drops? Seriously, you should do your first one across the battery top post to the post terminal, and work your way downstream. The terminal in the firewall connector is a known issue, so it's a sure thing you should check it.

Don't forget too, that a circuit doesn't stop at the powered device, people tend to overlook the negative or return path back to the battery. Voltage drops apply  on the negative side, too.

[Carrnutt]

Well at the moment, the drop is even at the main feed to the bulkhead connector, on the engine compartment side, so it starts before it gets past the bulkhead connector. The battery has no drop, the alt puts out fine. i can perform more tests during the week, i just ran out of ideas as to where to look and what to test  lol

[Paul G]

Dont forget about the engine ground and body ground at the battery. Mostly overlooked items when having electrical issues. Make sure those connections are clean and tight, as well as your battery cable conections, and the conections at the starter relay. Check conections down at the starter as well. They loosen up. What you are going to find is that, there will not be one thing that is causing it. It will be bad conections all over the place that cumulatively create a problem. The bulkhead connector will be a major contributor.

When doing your troubleshooting get a long jumper wire right to the battery, say the Neg side and test for your Pos volts at all the conections with your meter Neg lead right to the battery.

Hope this helps.

[Topher]

I use a Dremel with a side cutting fine tip to get down inside the female terminals and clean where the connections are actually made. It's time consuming, but you'll be surprised at how dirty they get. Then use a di-electric grease to pack inside the connections. This will keep them clean and trouble free for a long time.

I had a friend call me one time years ago on his 70 Mustang. He couldn't understand why it wouldn't crank after he'd just replaced the battery cables. 1st thing I did was grab the negative cable near the block to see if it was tight and the cable came out of the terminal. Just because something looks good, or is new doesn't mean it is.

[Nacho-RT74]

voltage drop is pretty much normal. Is like water loosing pressure along a pipe line

[Paul G]

One more thing, copper gets brittle with heat, humidity, age and gets less conductive. Look for oxidized, brittle wires as well as bad connections.

[TylerCharger69]

 

[Carrnutt]

Well, I gave up and discovered so many old splices in the dash harness, that i went ahead and got new dash and engine harness. Installed the engine harness (with the elect. and upgraded alt) and that fixed the problem. now I just need to figure out where to mount the Ign module and dual ballast. 

I saved a bunch of money thanks to the Year One codes from this forum. Thanks guys.

Oh I also plan on replacing all the bulbs i can with leds, outsides already done and dash will be.

[Nacho-RT74]

there are a thread made by autodinamics about the leds and HIDs on his 69... I'm not convinced yet, but is an option... search for it

[Carrnutt]

I actually went with http://www.superbrightleds.com   BA15 12-LED bulb red 1157 for tail / brake & 1156 for the taillights and 1157 amber for my front lights.  At $4.99 each times the 8 its only $40 total, plus shipping, and they just replace our bulbs, and look and work great.

I'm also going to use their wedge base and twist lock leds for my dash and gauges, all in blue, hope it looks as good as i think. I will post some pics, was planning on doing a small write up with materials list and whatnot.

[Nacho-RT74]

I wouldn't fit red bulb in back of a red lense

[Carrnutt]

You have to, a red lens absorbs all colors except red, thats how it works. An led doesn't have a true white (which is all colors) So you have to use the led that is the same as the lens color, unless its clear, like the amber in the front.

[Nacho-RT74]

well... try it, but I have my doubts. If you ask me put a red bulb on back of a red lense will decrease the given Lumens projection like putting a darker filter/lense color, at least that's with incandescent bulbs ( I work quite often like a lights operator on events ).

I can be wrong of course, but...

[Carrnutt]

Ohh it's already done   but yeah it is kinda against the normal rules of lighting, i had my doubts too lol

[Nacho-RT74]

mixing solid colors is one deal, but colored light is another diff story... could meet same results or not