78 F250, 460, Electronic Ignition (stock)

Does this thing take an internal resistor coil or an external resistor coil??? If external where is the resistor?????????

The alternator guy just told me all Fords had an internal resistor coil but the one that cam on this truck says it's for use with an external resistor. The external resistor coil ran a few thousand miles. Now every coil I mount gets fried after about 15 miles. I've gone through every voltage test I can find and can't find anything wrong.

This is without doubt the electrical problem from hell. :-)

Looking in my Detroit Iron Manual I can't tell. I don't see a resistor but I'm not sure I'd know one from a crankshaft. Well, actually I know what a crank looks like. :-)

 

It should have an external resistor wire behind the cluster.
The POS + side of the coil should have battery voltage on it in the start (crank) mode and about 8 Volts on it in the run (on) mode.

 

Yes, you are SUPPOSED to have an external resistor, but do the voltage check at the coil with the engine running to see what you really have.

 

I did find the resistor in the wiring diagram and with y'all's resposes the alternator guy must have been having a bad day.

By behind the "cluster" I'm assuming "instument" cluster?

I did the voltage checks quite a while ago and if memory serves they checked out ok except when it was running the voltage dropped very low. That may not be the case cause I'm good about forgetting things like that. I'll check them again.

That's if I can get it running again. :-) I'm going to get yet another coil today THIS TIME from the Ford dealership.

 

The old coil has Motorcraft 12029-ab. I'm pretty sure the letter before the 1 is an E butthe rest of them ahead of that are gone.

Does anyone know the motorcraft part number for a 78 ford F250 C6 460?

I'm not too trusting of the parts houses right now since they've sold me some internal resistor coils now. :-(

I searched the posts and see some hits on the 12029 but the other characters vary and i can't determine by search what is the correct number.

Thanks

 

I was going by the 1977 Ford Wiring diagram set and it says at the bottom that Splice S-302 is "IN 14401, BEHIND CLUSTER".
If you look at the diagram below you will see from where S-302 is in relation to the resistor wire in the diagram would suggest the it would be behind the cluster also. Yes I would think that they mean "instrument" cluster.

 

Stopped at the dealership on the way to work.

Ford dealer parts counter didn't have one, didn't offer to order one. How bout that?

They recommended I go to NAPA.

 

I went here www.partsamerica.com and looked up your truck. They sell the GP Sorenson coil, plus lots of others, including a Motorcraft coil if you want them to order it. This place is the same as Advance Auto in my area, it may be called something different where you live. All you have to do is give them the part number off the partsamerica site, and their computer on the counter will take it. I see no mention of internal or external resistor in the choices.

 

I found the Motorcraft dg-314 spec'd online today. Went online to Partsamerica after that and they shoe that coil probably in the same list you saw.

I can order it online but they'll only ship it to my house not the store up the street which is better for me.

So on the way home I stopped there to have them order it. Waited in line for 10 minutes and then wasted the rest of the half hour in there working with a kid that didn't no his............ from a hole in the ground. I told him I wanted THAT coil. They can't do anything with referencing 10 screens of computer output. :-) We finally got to the DG-314 and I tell him to order it and the computer quotes and orders a GP Sorenson coil. I said I wanted the motorcraft coil. Nope, cna't get that one even though they sell it. He could order the Sorenson but not the motorcraft. I could see in the picture it said "external" resistor only which is what I need so I said order that one.

Then we went on to the ballast resistor, want to change that too. Same ordeal, want the Borg Warner, it comes up on the screen and when he orders it it comes up with some cross referenced after market thing.

So I'm out o there with nothing. grrrrrrrrrrrrrrrrrrr Will try NAPA tomorrow.

Everything I touch turns into a weeks worth of work. I'm afraid to change a light bulb in the house. LOL

 

Dude! Where you get diagrams like that?????????? I got the Detroit Iron CD and they're anightmare to figure out. I finally figured out where the resistor was on mine but it would have taken a short time to see it on yours. Thanks

 

That diagram is mine, I drew it.
I used the big 1977 foldout Ford Truck Factory diagram as a reference.

 

Found a coil listed for this truck. Made sure it said on the outside of the casing that it took an external resistor.

Hooked it up, no spark.

Battery 12 v at rest
Battery 10 v under crank load
Positive lead connected to + coil - ~7 volts
Positive lead connected to coil under crank load - 8 volts

Guess what - the coil gets pretty damn hot just sitting there if the key is on. Supposed to do that???

I've seen a picture of the ballast resistor wire but I'll be damned if I see it anywhere. I pulled the gauges out and the ignition loose and I don't see it. :-(

I asked one mechanic I've used to take a look at it. Wasn't interested. Sent me to a guy he said everyone in these parts went to for difficult wiring problems. He went through a song and dance and said all these trucks used an internal resistor coil. OK, guess not the genius everyone thought. :-) He didn't offer to work on it either.

The old coil did say on the casing it was for an external resistor and it worked for 2 or 3 years. The later coils I got didn't say that in print but I watched them look them up at the parts store and they were listed uner 78 F250 460.

Am I going to have to buy another truck? :-)

 

If the resistor goes bad it can only open. Then you would have zero volts in the on (run) position.
You say 7 Volts at the coil with key in the run position so the resistor wire is OK.
I would change the Ignition Module, sounds like it is holding the TACH side of the coil at ground all the time.
Does the TACH side flash a test light while cranking?
Not sure about your truck but the ballast resistor wire on a tuck in the 80's look like this.

 

Thanks Subford.

I'll take this pic to the truck in the morning and see.

Not that it can't be bad already but I changed out the module when this problem started along with the voltage regulator. It's new enough I can get another one, no cost replacement. Worth a shot. The module I took out was only a couple of years old.

Sorry, never heard of the "tach side" on a module. Don't have a tach in this vehicle if that's the "tach" you're talking about.

 

What I was referring to as the TACH side of the coil is the other small wire going to the Ignition Coil sometimes marked with a - or NEG. In the diagram above it is circuit 232 a GR-Y wire (a green wire with a yellow stripe).

The Ignition Module pulses this wire to ground to make the Ignition Coil make the hi-voltage arc at the spark plugs.

In other words if you take an test light and put it on the NEG/TACH/- side of the Ignition Coil and the other wire from the test light to ground while cranking the engine it should flash. If it does not flash you will not get any spark at the spark plugs.

That photo above was for a truck with the ignition switch on the column, is yours on the dash?