Hot to the touch wire

[labuski]

Hey guys, i have a 75 model with 302. I am fixing some gremlins under the dash and stumbled upon a really long wire that looks out of place. It's peach colored (which could be discolored from how old it is).

The wire is attached to ignition switch and travels down the loom towards the gauge cluster, it then about-faces and goes back towards the firewall. I think it stops right before the firewall and is spliced into a few other wires.

The issue is when I put the key in the on position that wire starts getting really warm. Almost hot even. Even when the Bronco is not running, the key is just in the on position.

Is this normal? Maybe something is shorting? I don't know if this was something the PO did or is stock. When i get home from work today i will take a picture of the wire.

 

[Boss Hugg]

that's the resistor wire that feeds the ignition coil in stock form. Not sure how hot its supposed to get, but iirc, there was considerable heat in mine before I did my efi swap.

 

[Bogar]

The wire is a resistor wire. Lots of good information on here.

 

[broncodriver99]

X3 on it's likely the resistor wire. Also, you shouldn't leave the ignition switch in the ON position when the Bronco isn't running, use the ACC position instead. As you noticed that wire gets pretty hot and if running one of the aftermarket ignition modules it can burn it up, it may be bad for a stock points and condenser distributor as well.

 

[labuski]

thanks guys! so im guessing this is normal. I'll do further research now that i know which wire it is.

 

[Boss Hugg]

yeah, it's kinda scary, but I think it's normal. When I first found the issue, I thought it was the wire from the alternator thru the amp meter loop. nope. I had a pertronix ignitor 2 and when I did my harness swap (before going to efi), I left the resistor stuff out. I think the ign 2 was good on 12v. Maybe the first version also. Which means you don't need that heat source under the dash.... But if you're running ford electric ign or points, then yes, you need the resistor wire.

ALSO. There are resistors out there that would allow you to bypass the resistor wire and put the resistor under the hood away from anything that could catch fire.

 

[DirtDonk]

It's normal yes, but let's just say something isn't right still.
First, yes it's supposed to get hot. That's how it does it's job in fact. And it's also outside the normal harness tape because it's longer by necessity, and well, it gets hot!
For that reason though, that entire wire from a few inches after the switch to just before it splices into the other wires it's supposed to be covered with that tar-based fiber jacketing.
Sounds like yours is exposed in that pukey pink/salmon color all the way?

Might be trouble, or it might not. But at least we know it's working and has not melted anything around it yet it sounds like. But look around to make sure it has not overheated anything, or melted some harness tape next to it, or something like that.

Like ahuggins said, you have options.
You can replace it with a new one (kind of a pain).
You can bypass it with regular wire and use a ceramic base ballast-resistor under the hood. Still kind of a pain, but maybe a little easier.
Or you can simply bypass it and use regular wire the entire way and replace your ignition system with one that's meant to run on the full 12v instead. Rather than the basically 6v system these rigs came with. Hence the resistor wire in the first place...

My vote is always replace the ignition stuff with new 12v stuff for a better spark and fewer issues. But unless you are already replacing your old with new, this is by far the most expensive option.
Resistor wire is cheap. Heat jacketing is cheap. Leaving it alone if it's not a problem is cheaper still.

But if you have the choice and have already replaced your stock ignition with stuff that can handle 12 volts, then a new wire would be your best bet.

Assuming you have a Duraspark distributor, the ignition control module already uses 12 volts. Only the coil is running off of the resistor wire. A proper coil, a regular wire, and you're on the road.
Don't do it if you're not comfortable running new wiring around under the dash of course, but at least it's an option to be aware of.

Good luck.

Paul

 

[labuski]

Dirt, I really appreciate you taking the time for such a detailed response. This place is truly amazing and its that way because of all the awesome people that make it up.

The resistor wire does have some sort of sheathing. With how long the wire was i thought for sure it wasn't original because it seems like such a waste to me.

Right now I am just getting the bronco driveable for summer with its current 302. I hope to swap a 351 i have sitting in the winter time. I'll definitely look into a better ignition system then.

thanks again everyone

 

[DirtDonk]

Yeah, it is kind of a waste from our end. But from the factory's perspective, I suppose they were being very clever and saving a whole slew of new engineering costs.
When the automotive world went from 6v systems to 12v setups, they kept the old indicator gauges and ignition components.
Since both would have been damaged by running 12v through them, the resistors handled that problem. Of course, adding their own problems.

But paying extra for a longer bit of insulated finicky wire that got hot under the dash seemed like a good trade-off I guess.
Just like when they came out with the 2G alternator and instead of just up-sizing the charge wire to what they needed plus a safety factor, they decided that using two smaller wires would be a good thing. Not the brightest Ford light bulb in their history...%)
So now they use huge 6ga and 4ga battery cable sized wires to do the job.
I'm just guessing, but they probably finally realized that using the same cables on all their millions of production vehicles brought the cost of them so far down it was probably cheaper in the long run to have done it that way anyway.

Anyway, at least you know it's not a problem for your rig yet. They do fail of course, but the running hot is normal at least.

Have fun!

Paul

 

[broncodriver99]

Yeah, it is kind of a waste from our end. But from the factory's perspective, I suppose they were being very clever and saving a whole slew of new engineering costs.
When the automotive world went from 6v systems to 12v setups, they kept the old indicator gauges and ignition components.
Since both would have been damaged by running 12v through them, the resistors handled that problem. Of course, adding their own problems.

But paying extra for a longer bit of insulated finicky wire that got hot under the dash seemed like a good trade-off I guess.

That is not the reason for the resistor wire/ballast resistor. It has nothing to do with the switch from 6v to 12v. The ballast resistor is simply a required component in a points and condenser system. It serves several functions and a cost savings was not one of them.

 

[DirtDonk]

Hmm, interesting. So when they were running 6v systems they still used resistors in the ignitions?

Paul

 

[broncodriver99]

Hmm, interesting. So when they were running 6v systems they still used resistors in the ignitions?

Paul

The only 6v systems I have messed with are old Ford tractors and yes they had a ballast resistor as well.

 

[Boss Hugg]

Ok, so maybe it has to do with how fast the coil can take charge? How much resistance did the 6v system use?

 

[DirtDonk]

Well hoopty doo!
Thanks for bringing it up then. I seem I'm gonna have to do some more research!

Paul

 

[broncodriver99]

Well hoopty doo!
Thanks for bringing it up then. I seem I'm gonna have to do some more research!

Paul

I will explain it in the other thread(http://classicbroncos.com/forums/showthread.php?t=286939). Gimmie a few minutes. It will be a fairly long winded post.

 

[DirtDonk]

Ok, so maybe it has to do with how fast the coil can take charge? How much resistance did the 6v system use?

There's a lot of that mystery stuff going on in an ignition. Dwell being very important. Too much dwell can overheat even a 6v coil.
But there are different internal resistance values, and even today the companies like Pertronix will recommend a certain coil for use with 6 cylinder vs 8 cylinder engines, or list the same coil for both, but recommend only 12v for one, vs using a resistor for the other.
So yeah, lots more to know than just 6v vs 12v systems.

Good this came up. Hope to learn something new.

Paul

 

[DirtDonk]

I will explain it in the other thread(http://classicbroncos.com/forums/showthread.php?t=286939). Gimmie a few minutes. It will be a fairly long winded post.

Good. Live to learn...

Paul

 

[Boss Hugg]

There's a lot of that mystery stuff going on in an ignition. Dwell being very important. Too much dwell can overheat even a 6v coil.

Dwell. Yes, I know that word. I dwell in Texas! LOL. (seriously tho, I'm new skool enough that I've only ever dealt with dwell when helping my dad work on old stuff. So I don't completely understand dwell.)

Maybe it'll be clear in the new/other thread^^^.

 

[DirtDonk]

Hope so.
Basically though, the amount of dwell is measured in degrees (crank or distributor, I'm not sure. But probably distributor) for the amount of time that the points are closed.
How long they're closed and allowing full current to pass through the coil's internal windings will effect the amount of heat buildup inside the coil. So a longer dwell time will make the coil run hotter.
I think the whole reason to measure dwell especially with points is to strike that balance between letting the coil absorb enough energy to create a nice big spark, but not so much that it overheats.

I could have that wrong, so wait for someone to correct that. But I believe that's the basic gist of the subject.
Not sure how the whole thing equates to, for example, a 4cyl engine having more "closed time" in the distributor than an 8cyl engine would, but I'm sure that's all part of how they design a system's parts to work together.

Paul

 

[broncodriver99]

Dwell, is another subject but it has to do with coil saturation and building and collapsing the magnetic field which causes the high, 35,000+V output(spark). It varies with the number of cylinders because a coil on an 8 cyl has to to fire twice as many times in a rotation as one on a 4 cyl. That is also why the coil resistance values differ with application.