So I am doing a swap from a 400 to a 460 efi and have some wiring questions on my 1978.

First off I would like to use all factory set up inside the cab as far as fuse box, ignition switch, lights...etc. does anyone know which wires need to be hot at all times at my starter solenoid to power up everything inside the cab as normal?

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The basic '78 stuff is pretty straightforward, but there are some variations between different model trucks. Some of which may have to do with whether the truck has gauges or lights in the dash.
Just like any other Ford, EVERY wire that's on the large stud on the starter relay facing the front of the vehicle is hot at all times. They're essentially connected directly to the battery via the main battery cable.

So the wires you have now should be similar to the following:
1. A heavy gauge Black w/yellow wire from the alternator's output/BAT post.
2. A same gauge Black (or black w/red, or Black w/yellow) wire from the starter relay to the cab. Some trucks have a common power stud/junction block over on the driver's side firewall where other wires joint up before going into the cab. Pretty sure not all have this stud. Could be another "gauges-vs-lights" thing. This is the wire you were asking about as well. It's the main power wire for everything else in the cab.
3. Sometimes there is a Yellow wire.
4. Sometimes there is a Blue w/black wire.

Do you need to know where these go? They all have constant power, so that's not an issue.
The EFI harnesses are usually stand-alone setups where the only things you need to make the engine run happy are:
1. 12v in START only.
2. 12v in RUN only.
3. 12v constant.
And 4 through 4 million and one involve grounds!

Basically, upgrade all of your main wires if they have not been already. For a 460 (what year by the way?) with all the bells and whistles you should consider at least the following:
1. Up-size your battery cables.
2. Up-size your starter cable.
3. Up-size your alternator's output from the original 10ga wire to a 6ga cable. Depends on what year model engine, and what alternator of course. But this is not to be ignored.
4. Add grounds even where there were none before.

If you didn't have a ground strap between the engine and firewall, add one. If you did have it, keep it in good shape.
If you didn't have a decent sized ground wire to the body from the battery, add at least a 10ga wire from the negative terminal to the body/fender.
Make sure that the alternator case has a good clean contact patch where it bolts to the engine. And even then, I would add a ground wire from the case to the engine.
This last is not necessarily necessary... But I usually add a strap or wire from the engine to the frame. There is not much that gets it's ground through the frame, but grounding the frame avoids it becoming some sort of RFI component to mess with a finicky engine computer.

As for using the stock original fuse panel, it's probably not the best idea. But it's probably workable if yours is in great shape. Make sure to remove all the glass fuses, clean the contact surfaces and put them back in noting that they're clean and tight.
Any extra relays or fuses for the engine control should be added and perhaps connected to a stand-alone fuse panel of your own install under the hood or in the cab. But if you need more fuses than you have already, don't hesitate to add them.
Are you getting any separate fuse panels from the donor truck?

Good luck. Always interested in how EFI conversions go for our trucks. Can't wait to see yours come together.

Paul

 

Hey thanks Paul for the thorough reply. I already have my efi harness in place in the truck (rough install). My engine is already in place (1989 460 from an f250) along with all my fuel system. I am keeping my fuse box to keep it simple only because I don't want to rewire lights and other stuff that is not required to run the fuel injection. I do not have the fuse panel from the donor vehicle. The efi harness is basically complete with only the wires will need to find homes for now.

i do see those wires but I was a bit confused because they split to smaller gauge wires to the Alternator regulator and other to other wires that I am not sure I still needed constant power on. I will check my wire colors in a bit and post what I have.

 

If you're going to use the alternator from the '89 (most likely I assume?) then you are correct that you do not need at least some of those anymore.

Since the '89 should be using an internally regulated alternator of some type (probably a 2g?) then anything associated with the old regulator is re-purposed or removed. If your new alternator has a connector showing a Green w/red and a Yellow (or yellow w/white stripe) wires, you will repurpose the old regulator wires of the same color. You still toss out the old regulator, along with the old Orange "field" wire, but the other two still have their original purposes intact. They now simply attach to the new internal regulator connector, rather than the old one on the fender, or core support.

This wiring I'm describing is only for trucks originally with an ammeter though. In those cases there were only three of the regulator connection points utilized. If your truck has a battery light instead, all four locations were used. But the new alternator still only needs the two additional wires for the regulator, along with the new larger gauge charge wire for the main BAT output terminal.

For the new charge wire, you can "get away with" a reasonably small gauge because of it's short run to the battery. But for the sake of overkill, and in case you ever decide to put in a more powerful 3G instead, or just because it's what Ford would have done, I would up-size it straight to 6ga battery cable and a Maxi-Fuse (or similar protection) of an appropriate size.

Paul

 

Yes I will be using the the alternator from the 89. Not sure if it's 2g but The only wires from the 89 alternator are the main power cable going straight to solenoid, and the green/red wire that gets power from ignition or switched power to tell it to charge. Which I believe will go directly to my existing green/red that originally runs to my voltage regulator. Correct?

so this is what I had originally on my 78 with Ammeter gauge... The plug with 3 wires is "hot" all the time because it gets power from the starter solenoid through that fuse link. Do all three of those wires (BLK/Yel, yel/blk, and red) need constant power or is it just the heavy gauge blk/yel wire?

 

By the way yes I will be upgrading later to bigger alternator so I will be upgrading the battery terminals with heavier gauge once I get to that point. I don't want to get to ahead of myself right now lol I just want get everything wired and running correctly first.

 

A 3G from a later Ford is good, but just make sure to get one with a pivot-mounting scheme like our 1Gs. Sometime in the mid '90s, they changed the alternator cases to bolt directly to the engines with no bracketry.

As far as "in the cab," are you asking about which wires to connect to the cab? If it's like an EEC4 5.0, there will be a start, a run, and then the harness will contain wires for the Oil and Temp gauge senders - or you can plug the truck's wiring onto the senders and not have to splice behind the dash. There will be the main power wire which goes to the battery + side of your solenoid/relay. You shouldn't need to mess with anything on that terminal lug, unless adding accessories or sourcing additional power for the EEC4 system.

I like the idea of a 3G on my rig, but I don't like the idea of losing my ammeter.

Are you installing the Thermactor (smog pump) stuff? If I were converting mine to EFI, (and I might) I would install every single emissions piece, and try to make the EEC pass all Key On Engine Off and KOERunning tests, just because I like not having any error codes. But I would also look at a catalytic converter as well, because even when these EFI engines are running dead-nuts spot-on, they emit some very strong-smelling exhaust, unlike the engines made before they started installing converters in 1975 or whenever.
It seems that the oft-maligned catalytic converters allowed the manufacturers to do some crazy things with cam profiles in the '80s, because they 'now' had converters which scrub away that strong smell. Think roller cams. So even though the truck doesn't require a converter, you may end up wanting one...

They might've wanted to use those cam profiles in the years before converters, but the resulting exhaust was too stinky - even 50 years ago!






I put a set of GT40P heads from a junkyard Mercury Mountaineer on my Mustang, and I actually drilled Thermactor passages back to the rearmost cylinder's exhaust port on each head, in order to avoid the "No Upstream Secondary Air Detected" error codes generated when the Thermactor passages are blocked or missing.
I simply used a hand drill to drill the accessory bolt hole deep enough to reach over the rearmost exhaust port, and then drilled a smaller passage up from the roof of the port to meet the bolt hole passage! Also had to drill and tap mounting holes for the Upstream Air tube. But it worked, and no codes! I also converted that car to Mass Air, so it shows that you can do the same level of work, and wiring, and attention to detail, if you do wish to take it to that no-error-codes level.

 

thanks for the advice i do have all the emissions equipment so i do plan to run it. I would like to keep it code free with no check engine lights. i would like the ammeter to keep working if possible with my current setup but i wouldnt mind losing it for a 3g setup.

i have already identified what i need on my fuel injection harness. I am now trying to figure out some of the wiring on my 78. i have schematics but they contain so many different configurations its hard to really tell which apply to my specific truck. What i meant by in the cab is what wires should i provide a constant 12v supply from my starter solenoid so that everything in the cab powers up like it originally did. my picture above shows my fusible link that was on my starter solenoid and i was wondering what wires from my photo actually need to have a 12v constant supply.

 

My truck has zero options other than the Ammeter and Oil pressure gauges, cigarette lighter and a step bumper, and when mine blew the fusible link on that main wire, nothing worked. No lights, no starter, no anything. I thought the battery had completely died until it sparked when I was removing it during troubleshooting... So you need that wire. Also there's probably a yellow one which powers your horn relay.

I'd say yes, you do want all of those wires connected to the hot lug on the solenoid. From what I know, you don't want to change any of the truck's wiring in doing the swap, other than tapping the EEC into the truck's Start and Run circuits. I guess you might need to run some more power into the cab to feed the EEC (relay) - are you mounting it in the cab? Although I'm pretty sure that you need to bypass the resistor wire in the Run circuit.

Not sure which gauge sender wires I'd use - I mean I'd rather stick with the truck's original sender wires, but there might be a reason to use the ones in the EEC4 harness - though I'm not aware of any. Probably a good way to pare down the engine harness for ease of installation and aesthetic reasons.

 

I could be wrong, but I don't think you want to remove even a single wire from the starter relay unless it was for the old alternator. Anything that was there before, that is not related to the old alternator, is still going to be needed for the truck.
You will need to follow the wires to their engine-related terminations to determine if they stay or not, but the large Black w/yellow wire that runs to the cab does indeed power everything. So obviously it has to stay since it has nothing to do with the new engine.

The old wires from the regulator are going to go away except for the Green w/red wire. Correct that you can now use that one for your new wire of the same color on the new alternator.
The good thing about doing a Ford swap into a Ford is that some of the wiring colors are going to be an exact match.
I'll have to do a little reading on why a 2G would not use a Yellow w/white wire as it's battery sensing wire, but if you don't have one, you don't have one. So I can't argue with that. Just doesn't make sense to me yet. Gonna have to look at a newer diagram.

All of your new engine's sensors are going to need to be retained to send the proper signals to the computer. But the engine coolant temp and oil pressure senders will not be compatible with your old gauges I don't think. Completely different signals from what your gauges expect. Unless you can find where they have a compatible range then, don't try to splice your old wires into the new just yet.
You may have to find/make new locations to put your old sending units into the engine to run the old gauges.

I don't know why you would have to lose the ammeter for a new higher output alternator? Our late-seventies ammeters were of the "shunted" type, rather than direct reading. Yes, your gauge only goes to 60a and your alternator may put out 100a, but I don't think the shunted signal is strong enough to go in and bend a needle or anything like that. But again, I could be wrong, so don't quote me just yet. Let others who have done the conversion chime in and explain why the old ammeters won't work.
The traditional direct-reading style where the charge wire comes in on one side of the gauge and out the other will not only fry the gauge and possibly start a fire, but would likely just melt all the too-small and too-long wiring anyway!

The cool "inductive" type that was used in the old Broncos and probably other Fords as well, was very safe and could not cause a fire itself even if overloaded. However, you'd still have to lose the ammeter in most uses of higher powered alternators because the original wiring is not of sufficient size for a 2g or 3g output.
Too bad too, since the inductive and direct-reading types were very useful and accurate and consistent. Our shunted type unfortunately is notoriously finicky and I would have to say that probably 70% of them in our trucks no longer work.
Mine only worked for about a week after changing a regulator one time about 25 years ago or so. Before and after that, zilch...

Paul

 

I think the Oil and Temp gauge senders should simply swap over from the original engine to the new one.



That is usually the contacts glazing up and impeding the current. I remember I used to notice that the ammeter in my old '82 GT 5.0 would always work better (larger range of needle movement) right after I'd removed and reconnected the battery. I think if you go through and clean/abrade all of the connections in the ammeter circuit, and protect/seal them, that the ammeter will work better, and for a longer time.

 

Thanks for all the replies lots of good information. I ended up looking up the water temp sensor for both trucks 1978 and 1989 and it looks like they offer the same part number sender so it appears that the water temp sender should work with my old gauge. They also offer the same part number for oil sender but only for trucks with oil indication light? So may not be compatible with trucks with actual gauges.

Also, for my switched 12v signal should I tap into my ignition switch inside the cab or is there a wire outside in the engine bay that has ignition 12v? I didn't see one but I could be wrong. This will be to activate my eec and fuel pump relays. Also, to provide 12v to my oxygen sensor.

 

Should be at least a couple of switched wires under the hood. Old ignition, old voltage regulator, old high-idle solenoid (if so equipped), stuff like that.
If choosing the old Red w/green ignition wire you would use it to trigger relays though, instead of powering accessories directly. It's the business end of the resistor wire, so while it's fine for the low load of a relay, it does not have the capacity to flow the current/voltage needed for most other tasks.

As for the senders, as long as your computer uses a separate sender for the information it needs and the engine has a separate one for the gauges, you're set. But if any of the sensors do double duty, you can't just get rid of the new one and put an old one in there or the computer won't know what it's seeing.
So if there is only one coolant temp sensor on the engine, then you will have to leave it and install a secondary sender for the gauge.
From your searching it sounds as if they are separate, and that the gauge senders are one and the same for new and old at least in some cases. So that's a great start.

In all the EFI swaps I've done there were always relays to power things like the ECM, fuel pump, O2 sensors, and stuff like that. Anywhere from three to five relays in the harness. You could take the old Red w/green wire from the ignition coil and use that to switch on the relays from a common terminal.
I always end up with at least one, but usually two, of the nice old GM power point studs that I scrounge from junkyards. One stud will be for constant power from the battery that I can then, attache multiple other wires to. The other will be a switched power source from one of the previously mentioned wires.
There are brand new studs and terminal strips easily available, but I really like the look of the OE stuff.

You could use the switched wire from the old regulator (Green w/red), but in your case it's still going to be in use with your new alternator, so the old Red w/green ignition wire seems a good source if you're just tripping relays.
You may also find a Black w/green wire under the hood that would have been used to switch on the dual-battery isolator relay. Any Blue wires on top of the engine would likely be switched 12v as well. Carb idle solenoid, and float bowl vent solenoid functions.

Paul

 

Excellent! Thanks for that info. Never tried messing with the gauge itself.
But my next go-round is going to be with a Dakota Digital cluster anyway. Been wanting to try that for a long time and finally spent the money.
Of course, I did that right before they came out with the VHX series cluster! I hate it when that happens!

I actually really like the full digital readouts. But I still prefer a nice analog-looking face when I have the option. Spent a lot of time in an old Cadillac with digital gauges and though I thought I'd hate them, after only about a day decided that I really liked them.
But those VHX setups are sweet!

Anyway, I won't have an ammeter in the cluster anymore, but they have a nice digital ammeter that I will use separately.

Paul

 

I should have added that, yes you'd be perfectly fine running a new wire from the switch if you wanted. Nothing wrong with that. Just wanted to mention the other wires already under the hood that I thought might be usable as well.

Paul