f150 won't start on just 1 battery

[DennisG01]

I love the bucket analogy - so true!

Voltage drop is a great test to locate/narrow down where a problem is.

You mentioned 13.1V at the battery. With that reading, I assume it was right after turning the charger/engine off? Even a new battery won't show that high of a voltage at rest. Check the resting voltage after sitting for a day or two, or after a quick attempt at starting the engine. I agree that there's most likely something causing extra resistance, but don't rule out the batteries - they are a variable and you may want to eliminate them from the list by getting them checked out again.

If you haven't removed, cleaned, reinstalled (tight) ALL connections, both +/-, from battery to engine, do that too. Don't assume they are clean by just looking at them.

Check your battery switch, as well - connections (clean and tight) on the back side. They're generally a very reliable piece of equipment, but they do occasionally fail internally, too.

[rodbolt17]

that is because it was not corrosion.
it was oxidation.

same results but different causes.

[DennisG01]

Very often, you can see that black oxidation when you peel back the sheathing of a wire - to fix a crimp, add a new circuit, etc, etc. It will completely cover every single strand of copper wire. The corrosion/oxidation wicks it's way up underneath the sheathing. Ideally, you keep stripping the wire back till you get to clean copper. But often it goes quite far - sometimes I will carefully scrape the black off with a razor blade, moving the strands around to get to all of them.

I typically use a heat shrink connector when I put a new connector back on to hopefully keep the oxidation at a minimum. I've also had VERY good luck using a product called Tef-Gel - it's expensive, but a little goes a long way and it does not inhibit the flow of electricity like dielectric can... which should, in a perfect world, only be applied after the physical connection is made.

[fairdeal]

product called Tef-Gel - it's expensive, but a little goes a long way and it does not inhibit the flow of electricity like dielectric can...

I curious why you accept that Tef-gel (40% PTFE powder in grease) does not "inhibit the flow of electricity" if applied to an electrical connection

but think that silicone ("dielectric") grease does

[DennisG01]

I was turned onto Tef-Gel about 10 years ago from someone I consider much more knowledgeable than me, who had been using it on and around boats for as long as he can remember. I consider myself somewhat anal about maintenance, but this guy puts me to shame. Tef-Gel specifically states that it does NOT electrically insulate electrical connections. Even so, I called the company and talked to them at length about that point and they stated, over and over, that used as directed it will not hamper the electrical connection.

As mentioned above, dielectric is DESIGNED as an insulator - which is why it's recommended to use, for example, on the outside of spark plugs or the inside of the boots (not the electrode) - to insulate the contact area between the plug casing/insulator and the boot to keep moisture out or stray current in.

That said, I've certainly used it on electrical connectors with no ill effects that I'm aware of. Knowing what I know now, I do try and avoid it in compression type connections (battery terminals, for example). But I think it's probably just fine in "slide together" connections (like bullet connectors) where the two connecting metals slide together, likely wiping away the grease as they go. However, it's still better to use the dielectric AFTER the connection is made.

[99yam40]

even when you put some on connectors and then make them up the grease squeezes out of the way and you get a metal to metal connection on most of the surfaces. The grease just fills the voids and keeps the O2 and other contaminates out reducing the chance of oxidation or corrosion

[rodbolt17]

LONG before I start randomly yanking and cranking I will spend the 8 min or so with a meter finding at least which part of the circuit has failed.
saves me time and my customers a bit of loose coin at 100/hr.

[DennisG01]

even when you put some on connectors and then make them up the grease squeezes out of the way and you get a metal to metal connection on most of the surfaces. The grease just fills the voids and keeps the O2 and other contaminates out reducing the chance of oxidation or corrosion

I'm not arguing that Dielectric can work - as I mentioned, I've used it many times. I'm just offering that there's a better "tool" for the job that is specifically designed for the purpose.

[99yam40]

it is just like most greases and is not conductive.
now if you use a metallic antiseeze ( contains metal particles) then it could be conductive

" The function of Tef-Gel in eliminating dissimilar metal corrosion is the elimination of electrolytes from entering the interface of the metallic surfaces. Tef-Gel paste contains 40% PTFE powder and 0% volatile solvents, no silicones or petroleum solvents to evaporate, which would leave voids for electrolytes to be drawn into creating a galvanic cell. When both surfaces are coated and mated with Tef-Gel there are no voids for electrolytes (saltwater) to be drawn in by capillary action over extended periods of time."

[DennisG01]

The only thing I'd be concerned about using Tef Gel is if packing a multi wire connector, will it help current trickle out elsewhere where it shouldn't be...

Now if just on a separate wire, battery terminal, no problem obviously...

Hmmm. Interesting thought. If I'm understanding you correctly, in essence you're wondering if it will carry electricity? I use it VERY sparingly - just a very light coat of it. In your example (you're thinking multiple wires butt connected?), I would only coat the actual strands. Since the strands should be cut short enough to stay within the butt connector, the answer probably doesn't matter. In other words, I would never glob this stuff on - for one, it's unnecessary, but it's also too darn expensive to waste!

If I think of it later on today, I'll give them a call and ask that. My assumption, though, is that it wouldn't really carry electricity - just that it doesn't impede the flow of electricity in close contact. But I suppose if we really want to do things "overboard", we could use Tef-Gel on the contact areas, then assemble the joint, then apply dielectric afterwords!

[DennisG01]

These are the tiny wires/connectors that I referred to. Potential electrical leakage to other wires...

I'll ask them specifically about that - it's a little different (and possibly more "temperamental") than what I was thinking. Shrouded, small pin plugs can be hard to get anything, other than a spray, properly applied. But there's an example where the two metal pieces are sliding against each other and wiping the grease away so it's probably one of those cases where just about anything would work, even "normal" grease.

[DennisG01]

That dried salt on those connectors OFTEN "shorted" and caused running issues.. Not unusual at all...

Absolutely - couldn't agree more! Air is a fluid but when you add salt to it, it ups the electrolytic conductivity. It creeps it's way into the tiniest crevice and can make problems/diagnosis very difficult.

[DennisG01]

Got some good info from Tef-Gel that helps to clarify everything, including some mis-representation on my side. It is NOT conductive. It is technically an insulator, much like Dielectric is. Where it differs is it's ability to withstand greater heat and chemicals/acid, along with covering those "gaps" where corrosion can seep in to a smaller, more microscopic level.

[99yam40]

same as I posted in post #35

[gsdanno1]

Here's where I am . I had voltage at the nut on the back side of the battery switch at 13.1 . The voltage on the posts was around 8 on the #1 post , and 11 on the # 2 post . I replaced the battery switch , I now have 12.6 +/- at the posts and the nuts. I also replaced the power posts and voltage is 13.4 , although the main battery cables to the motor don't connect here , so it really has no bearing on the problem. I have 14 volts at the starter , when I crank the motor , voltage drops down to 8 volts . This is where I have stopped . I haven't done a starter draw to check amps yet , that will be my next step . Timing is good according to the yds . I don't quite understand why the voltage is lower at the battery switch than anywhere else