Yes my alternator looks like the one on the right and the new harness wont connect to it.

 

Okay, you have the uncommon 70 amp alternator. I've actually never seen one on a truck, I've only seen them on industrial engines. They were available on the F series trucks as an option but was rarely ordered.
The correct harness for the '78 w/ warning lights and a 70 amp alternator is D8TZ-14305-A.
I located 3 harnesses but the problem is Bob Allen Ford, (913) 381-3000 in Overland Park, KS has all three. Bob Allen has a terrible reputation for pricing on obsolete parts. I couldn't find any other dealer or obsolete parts supplier that has one.
Check the price that Bob Allen wants, it might be cheaper to get a 60 amp alternator to match the wiring harness you have.

 

My alternator is from AutoZone, I just double checked the part number on my alternator and autozones and it shows it as a 70 amp alternator w/ warning lights and alternator connector. They also show a 60 amp alternator w/ warning lights without the alternator connector which would match your picture. Can I just exchange my alternator for the 60 amp one or do I really need the 70 amp one?

Alternator that I have on my truck with alternator connector:
Valucraft/Alternator (7072) | 1978 Ford F250 3/4 ton P/U 4WD 8 Cylinders H 5.8L 2BLModified OHV | AutoZone.com


Is this the alternator I need to make the new harness work? I cant wait 2-3 days for another harness:
Duralast/Alternator (DL707P) | 1978 Ford F250 3/4 ton P/U 4WD 8 Cylinders H 5.8L 2BLModified OHV | AutoZone.com

Seeing as how the 70 amp is uncommon maybe the previous owner swapped it in, that would explain the hacked up wiring at the alternator? Did the 60 amp and 70 amp alternators use the same voltage regulator? If not then that could explain the regulators burning up because I replaced them with stock ones.

I will go ahead and pick up a 60 amp alternator to match the new harness. 2 questions now. How come my new harness doesnt have a ground wire like your picture shows? On the voltage regulator connector theirs a fusable link, what is this for? Electric choke assist?

 

The fusible link should have a 5/16" terminal on the end so it can connect to the battery terminal of the starter solenoid, at least that's where the one on my harness connects.

 

The orange plastic peice is the 16 gauge fusable link, this is the one that goes to the battery side of the starter solenoid correct? What is the yellow wire with a black thing on the end for? it looks like a bullet connector for something.

 

Yes, that black/red wire goes to the battery terminal side of the starter solenoid.
The yellow wire with the butt connector is for the radio suppression capacitor. It looks like a condenser and is attached to the regulator. If you don't have one, don't worry, it's not necessary.

 

Yeah I dont even know what a radio suppression is so I dont think I have one as my truck doesnt have a radio.

Got the new harness in, new voltage regulator, new 60 amp alternator and I changed the battery cable ends to brass ones. Turned the key on, ALT light came on. Started the truck and the ALT light turned off everything seemed normal. Took the truck out and it ran better than it did. Before I couldnt even go up a hill in 4th gear and now it climbs steadily.

Thanks FMC400 and mikeo0o0o0!!

 

Glad you got it fixed . Thanks for the update.

 

Man I really hope the two posters who help the OP are still here.

I too have the same issue as the OP. I had a brand new swollen battery in two weeks. I replaced solenoid, new bat, and regulator. Now doing the alternator. I think the engine was overheating the alternator as some the connections are melting and there was no connection at all to the STA stud. I’ve been able to follow along but I have one difference. I’m having trouble identifying if I need a gauge or idiot light harness. I have the green with red stripe wire going to cab. Problem is it looks like the the other wire was cut that ran with it to the connector. It was also cut on the male side of the connector wire as I only have one wire going to the S tab on regulator again nothing to STA stud. I just need this thing to run and charge without burning alternators and batteries I could care less about gauges or idiot lights. It’s basically a farm truck. Would appreciate some help on which connector and who has em.

 

mikeoooo do you know if these are still available? Also are you keen to identify which I need based on the info in the above post. Appreciate the help.

 

Do you have a volt-ohm meter handy? If so you can check your running voltage at the battery with the engine idling. Should read about 14.5v at the battery for proper charging. As low as 13.8v or so is acceptable, but not optimal. Anything over 15-15.5v is too high, but if it's at 17v or so, you now know why your battery was fat!

FYI, solenoid/starter relay has nothing to do with the charging system other than being the middle-man and a handy way to connect things. But it has zero to do with the battery over-charging.

Which one does yours look like from the pics above? As was said, the large-case 1G in 70a or 105a rating was a rarity in trucks, but anyone can swap them in (which is what I did on my '79) so just to be sure, let us know which one you have.

Possible, but VERY unlikely to be engine heat melting wires unless they're literally laying on the hot parts of an engine. Usually not enough heat for that.
Most often melted wires are from too much current flow for their gauge/size. Which could be consistent with your possible over-charging condition.

What year is your truck? Does it have an electric choke on the carburetor? They came into regular use in '73 for some trucks, and this is the '73-'79 forum, so yours would normally have had one. But that might have changed for various trucks and various engines. Others will know more about that than I do.
But this comes down to your gauge package too. Do you have a "BAT" or "ALT" or "CHG" gauge (ammeter) in the instrument cluster? Or just a series of warning lights?
If lights, then you need the STA wire. If gauges, you don't need it for the charging system at all. Only for the electric choke.

All depends on your dash layout. Is it together, or apart and perhaps missing? Sounds like the truck was running, so I'm assuming you have the instrument cluster installed?
Let us know, or post up an image of your dash.

What color was that other wire? White w/black perhaps? Which connector? Got a pic?

Again, might not be a problem.
If the wire to the S terminal on the regulator is Green w/red and has battery voltage on it when the key is in RUN/ON (but not ACC) then this can work.
Again, with the gauges you don't have to have the STA stud on the alternator populated for it to work.

That might make things easier, but let's do some testing and checking and look-seeing.
If this is a gauge truck, then only 3 positions on the regulator connector are used. They are:

1. F - (for Field) is the Orange wire that runs straight from the regulator to the FLD terminal on the back of the alternator.
2. S - (think "switched") is the Green w/red wire and runs straight from the ignition switch. Should have close to full battery voltage with the key ON only. Nothing when the key is OFF.
3. A - (think "always") is the Yellow (or Yellow w/white) wire and should have full battery voltage at all times.

If there is no voltage on that Yellow wire with the battery connected, or if it's substantially lower than battery voltage, your alternator will always think that the battery is low and keep charging when it's not needed. This is where a volt-meter is your best friend.
General practice, never connect the regulator to the battery until the regulator is grounded to the body. But you can connect and disconnect the plug while the battery is connected and even if the engine is running, as long as the regulator is fully grounded.
And as discussed in the older posts, the GRD post on the back of the alternator should have a dedicated wire running from it to one of the regulator's attaching screws. And a for good practice, the body/paint area where the regulator mounts should be clean and rust-free. Having no paint is not a bad idea either, but in reality they can get a good ground just with the screws through the body like Ford did it when new.

Other points to note, are your battery cables and connections everywhere. If there is a lot of rust or even a lot of new paint, some of these connections might not be working properly and your system is getting false signals.
Good practices for a happy electrical system are:

The main ground cable (I prefer 2ga or larger on trucks) to the engine block directly. Not to an alternator bolt or bracket. Clean rust-free location.
The alternator should have a good clean contact point to the engine block. By now lots of rusty threads and painted surfaces can cause issues. It's not a deal-breaker as we've certainly got a lot of old trucks still charging, but it can't hurt to keep contact points clean.
Depending on which alternator you have, you can get away with as little as 10ga wire for the main charge circuit between the BAT terminal on the alternator and the battery side of the starter relay. But this is a point where a little bit of overkill is not a bad thing. Especially if you're running a 70a or higher output alternator!
If you have access to 8ga you can pretty much use any of the old alternators. Anything more modern, such as a Ford 3g with 95a to 130a output and you should be using 6ga battery cable. If Ford thinks it's justified, so do I.

In fact, if all this wiring nonsense makes your head hurt, you could just as easily (in most cases) install an internally regulated 3G and be done with it. You'd still need to connect the Green w/red and the Yellow wires from your old harness to your new alternator, plus add the larger charge wire for sure.
But they're easily available, fit the old standard brackets (not sure about those with the Thermactor/air pump though) and lets you get rid of the old separate regulator on the firewall.
The only added "hassle" is that you would need to extend the old wires to reach the alternator instead. Very easy though.

Anyway, hope all that helps. Threw in a lot of extra fluff and options, but hopefully covered the basics.
Once you show us which style of alternator you have, and the dash layout, we can confirm more stuff for you.

Paul

 

D8TZ-14305-C .. Alternator to Voltage Regulator Wiring Harness - Use with Oil/Amp WARNING LAMPS / Marked with ID number: D8TB-14305-CA / Obsolete

1978 F100/350 & Bronco with 40 & 60 amp alternators.

MILLER OBSOLETE PARTS in Vestal NY has 1 = 607-722-5371.

GREEN SALES CO. in Cincinnati OH has 38 = 800-543-4959.
--------------------------------------------------------------------
D8TZ-14305-D .. Alternator to Voltage Regulator Wiring Harness - Use with Oil/Amp GAUGES / Obsolete

1978 F100/350 & Bronco with 40 & 60 amp alternators.

You'll have to call Don Sanderson Ford (623-842-8643) to see if they still have it, their webpage hasn't been updated in months.

No other Ford dealer or obsolete parts vendor has these two wiring harnesses, none on ebay.

 

Thanks for the replies guys. Finally getting a chance to get back at the truck as the 1st cutting of hay is done. First, I want to point out like a dummy I didn't realize I was following a post/forum for not my year of truck. I have a 70' F100. I did buy the gauge wiring harness from Green Sales and it doesn't fit...duh.

1. My original connections were all jerry rigged to start so I am trying to make this work. Here is what it looked like. I took apart all the connections to try and figure it out. The red at the top of the screen is the wire that goes to solenoid. It was spliced to the fuse link in picture. The black wire from right of screen is what I believe the main power coming from alternator. It loops back from the bottom of the picture and the red wire in the cluster and wire with fuse were all spliced together. The yellow and black from the cluster as you can see were spliced off that main alternator line that the fuse line, solenoid wire, and red wire to cluster are all tied into. Yes I know its a mess and what I think was causing my issues.


2. Here is how the new harness looks from Green Sales. Couple issues, one its no where near long enough and two I am missing the three wire cluster. It only has the two wire cluster.


3. Here are the connections I need outside of the regulator, alternator, and solenoid. Also, previous owner cut the yellow wire on the two prong cluster, don't know why or what it does. Truck was running prior to all this.


So I guess my question is this. Is there a correct wiring harness I can order out there for my 70' F100? If not can I simply splice the three prong cluster below the fusible link and then extend a 16 AWG wire to the solenoid like previous owner did? The current wire harnesss for that black wire is 16 AWG.

Here is what my dash and engine compartment look like. Also a look at the fried connection wires to the alternator. Again there was no stater wire as it appeared to be burnt off. Really appreciate the guidance here.

 

Well that'll mess things up! Ford was not known for keeping things consistent over the years, but especially with model changes.
At least the wiring colors are "mostly" the same between the years, so we can figure some of the stuff out. Sorry I'm not familiar with the earlier connectors, but maybe can figure it out.

Yikes! A mess-o-wires for sure. But hey, people have to do what they have to do sometimes to get something back to working. Especially on a job-site or ranch/farm situation. So maybe we'll cut some slack for that possibility. If it was just laziness or lack of knowledge, all bets are off!


So the Red wire and fusible link were on the large stud with the battery cable then. Correct?

The black wire from right of screen is what I believe the main power coming from alternator. It loops back from the bottom of the picture and the red wire in the cluster and wire with fuse were all spliced together.

Yes, should be. Usually the largest wire on the truck (short of the battery cables of course) is the charge wire, then the battery-to-cab wire. Or in the case of some ammeter equipped vehicles, the "charge loop" that runs into the cab then back out to charge the battery.
Either way though, it is the main power wire and will sometimes have a yellow stripe/trace.


Sorry I'm not remembering what the Yellow w/black wire is for. I don't keep my early wiring diagrams handy enough, but have saved some that were posted by others here. So I might be able to figure it out. Hopefully though someone that knows for sure can chime in first.
But I've already seen a couple of issues with the charging. One of which looks like the Orange wire had full battery power to it at some point, and if the other end was connected to the FLD terminal of the alternator, that would explain melted wires, overblown batteries and overheated alternators.


Yep, a lot was changed in the early seventies regarding wiring, so it would not take much to make a harness incompatible.
Not to mention (which I am going to do anyway obviously) the alternator connection is wrong. From the picture at the bottom you have a full-gauge instrument cluster, which means your regulator only uses 3 positions of the regulator connector. Your new one is for warning lamps instead of gauges.
Too bad though. Nice to have all new wires!


On Ford trucks at least "most" of the solid Yellow wires were direct battery power to something.
Under the hood one wire was for the "A" terminal of the voltage regulator and was typically spliced to the large Black battery wire somewhere in the harness nearby.
Another typical Yellow wire was used to power the horn relay under the hood. I believe your truck should have been so equipped. Is there a semi-triangular shaped 3-wire rubber connector and a small silver box hanging around that area by any chance?


Number Dummy to the information-rescue?

Doesn't sound right, but just about anything can be done.
However to use the new harness at all, the first thing you would to (after finding out if it's returnable?) would be to re-pin the 4-wire regulator connector to the correct order.
But we'll still need a bit more information and maybe a few more pics for that. We'll see.

It's very possible that your '70 did not originally have a Stator wire. Not sure if all trucks were wired this way, but in '70 the normal scenario would have been Warning Lamps = Existing Stator Wire but Full Gauges = No Stator Wire (until '73-ish)

Those alternator wires were not overheated from engine heat. They were fried in either an over-charge situation where the alternator ran out of control, or a full short-circuit to ground after some of the outer jacket melted down.
That's probably the most likely way it happened. First the jacket melted down from the heat of over-use, then once that happened some unprotected wire somewhere along the line touched metal or another wire and POOOFFFF!
It's probably not the only way this can happen, but it seems very likely here.

Thanks for the dash pic too. Shows what we need to know for the regulator wiring.
See how your new connector has 4 positions filled? The correct one will have only 3.
For your reference, the correct wire orientation for your voltage regulator is as follows:

1. "F" is the Orange Field wire and runs straight from the F terminal on the regulator, to the FLD post on the back of the alternator.
2. "S" is the Green w/red "switched" wire and runs straight from the ignition switch to the regulator.
3. "A" is the Yellow (always hot) power wire and is connected to the battery positive section. Usually spliced into the large black wire, it can be run anywhere you can, such as to the starter relay's battery post, or the battery directly, or spliced to a battery wire if you want.
It just needs to always have 12v so the regulator can sense what the system voltage is and, through the Orange wire, tell the alternator what to do.
The Green w/red wire just needs 12v when you turn the key to ON to tell the voltage regulator to "turn on" and be ready for the alternator to start spinning.
The Orange Field wire is literally the communication connection between the regulator and the alternator.
And of course the large gauge Black wire is where all that current goes to feed the truck and charge the battery. But it's always powered up whenever the battery is connected too, which is why you need to disconnect the battery (usually just the ground cable is enough) before working on the alternator or the regulator.

And a voltage regulator should never be connected to power when it's not grounded to the body. Apparently you can fry your internals in seconds if you apply 12v to the regulator, but not have it bolted to the body.
Just a heads-up while you're messing about with this.

Once you see which circuits are the important ones and where they go, you can see it's not the crazy mess that the mess under your hood makes you think it is. Just that it was messed up by someone when they went-a-splicin' and now looks more complicated than it is.
It's easy to make your own sometimes too, if you can't find a new one.

Good luck!

Paul