I checked all the fuses under the steering wheel for continuity, and all the fuses are good. How do I check to see if the fuses are getting power?

 

Ok, we'll assume the cab ground is not the issue. Were back to +12V supply to the cab.

To check that the fuses are getting power:
1) Set your multi-meter to DC voltage
2) Take the negative lead of your multi-meter and place it on the body of the cab. Again, make sure where ever you place it is bare metal, no paint, grease, etc.
3) Now take the positive lead and place it on the metal portion of the fuse you are checking.

I suspect that you will not have ~12 volts at any of the fuses inside the cab.

Regardless of what you find, report back and we can continue to provide you with suggestions.

 

Thank-you for the help.

Also redid #2 from the previous post using a couple different spots inside the cab instead of the bolt used to hold the side mirror onto the door: metal on transmission shifter, metal on turn signal lever, metal on door window handle, metal on door handle, metal on clutch pedal, and with all of those the headlights won't turn on.

Also, I checked all the fuses for power with the multimeter, and none of the fuses are getting power.

 

Alright, we will focus on your +12V supply to the cab.

Do you have the ability to take a picture of your starter solenoid?

Provide me with that picture and we will get started on tracing where the interruption is.

 

This may be a help...

I think the fusible link may still be the issue. It would prevent the light switch from getting any current, as well as the ignition circuit and the accessories.

When you bought and installed the new fusible link, what size (gauge) was it - and HOW did you install it? Look at step 5 below and test your fusible link to make sure it has continuity/low resistance.

How to install a fusible link:
1) Locate the "fusible" section in the existing wire
2) Cut a fairly large (1-4") portion out of the old wiring harness to remove the burnt out "fused" section
3) Strip the wire insulation back 1/4"-1/2" on each end of the existing circuit, and an equal amount on both ends of the replacement fusible link.
4) Solder the new fusible link into the circuit and then cover them with shrink tube and electrical tape.
4a) If you can't solder, and can't find anyone to help you solder the link in place (any electonics repair shop can do it in about 2 minutes), then crimps are an acceptable SHORT TERM solution. I don't like crimps - after a short time, moisture will get in the joint and they will corrode, leading to another failure.
5) Test the new fusible link with the multimeter
5a) Set the Multimeter to OHMS (the Horseshoe omega looking thing)
5b) Put one test lead on one end of the wire, the other lead on the other end
5c) If the multimeter reads "0" you have continuity (0 resistance - a good thing for a fusible link). If it reads more than about 1ohm, you have a problem.
6) Reinstall wiring harness. Make SURE all the connections are clean and tight and IN THE RIGHT PLACES!
7) Test the headlights. You might want to have someone stand in front of the truck while you turn on the lights. If the fusible link you bought is TOO SMALL, you're likely to get a brief burst of light before it burns out again.

Let us know - you can also skip to step 5 and test the existing/replacement fusible link to see if it has continuity/no resistance.

-Brad

EDIT: You should check ALL of the wires in that harness for continuity end-to-end, and make sure they're all good.

 

I'm having trouble finding the usb cord from my camera to get my pictures onto my computer. But, the connections on the solenoid are the exact same as those in this picture.

Ford Truck Enthusiasts Forums - View Single Post - Need help Hooking starter back up

 

Thank-you for the help.

The fusible link I used was a universal 16 gauge fusible link, the same gauge as the previous fusible link.

I checked the new fusible link for continuity, and the fusible link measured at 0 resistance, so the continuity for the fusible link is good.

 

From wiring diagrams i believe there is more than 1 fusible link for your truck. My truck is at my shop so I can't say for sure, but according to the wiring diagrams, there should be three fusible links, 1 for the charging circuit, 1 going to a junction ("L.H. side of the dash panel"), and another going to the ignition switch, headlight switch and other constant power accessories.

From your post i believe you replaced the fusible link for your charging circuit (e.g fusilbe link going to your alternator).

You need to look for the other fusible links that go into the cab and test them for continuity. Next time i'm working on my truck I'll take a look at the wiring to see if can give you any hints to where they may be, color of wires, etc.

 

Excellent! That means you also learned how to test wiring for resistance - anything that's supposed to be connected (like something that's supposed to be grounded) you can now check! Combined with using the DC Voltage setting on the multimeter, you can check almost anything electrical in the truck!

Was the fusible link you replaced in the Black/Yellow wire? (That's what the '78 shop manual shows, I don't know the exact colors for all the years, but I think they're fairly consistent). I would check all the rest of the wires in that harness for

The shop manual seems to think there's a fusible links in the following places:

-16ga fusible link somewhere in the heater/AC circuit near the starter relay (most likely not the problem)
-16ga fusible link near/at the starter motor relay in the alternator circuit (the one you replaced, I think)
-20ga fusible link at the electric choke, in the alternator circuit (most likely not the problem)
-20ga fusible link at the starter relay in the marker light circuit (most likely not the problem)

The shop manual also says that there are various circuit breakers (on the headlight switch, as the most notable example). However, these shouldn't be the problem either :-/

I wish I could see exactly what was going on! It's frustrating that I know I'd be able to help find the problem if I could see it and trace the wires in person

-Brad

 

If you are not getting 12+ volts on the battery side of the fuse box than try checking the resistance from the battery side of the fuse panel back to the battery. You will have to make some extentions for your probes with some 12 ga wire or larger. If the resistance is high than start tracing wireing back to the battery which I believes goes through the solenoid connections. Can we assume that the truck was originally a single battery system? If not this can add some complexity to the tracing and trouble shooting effort. Hope this helps.

 

I don't know if this will help, but the schematic at this link shows 4 fusible links.
http://www.justanswer.com/uploads/cr...ruckwiring.pdf

Also, what is the history of this problem? You say in your initial post it won't start and seems to have no electrical. Is this a thing that started while you were operating the truck, or was it like this when you got the truck?

 

I note the schematic has an "accessory relay". I am not very familiar with models as late as your '78, but I wonder exactly what function that serves in terms of your lights and so on, and if it should be considered a possible culprit.

 

After looking at schematics for an hour my first test would be a black/yellow wire from the starter relay (there are two) that has a split in the harness to an orange wire and a yellow wire. The yellow goes to the ignition and the orange to the light switch. My thought is that it is cut between the split and the starter relay.

My second test would be to visually inspect the printed circuit board for any burning or obvious damage as the fuse box sources come from that board. However it is not obvious to me how this would affect the ignition switch.

Please let us know what you find! Also, any and all photos would be appreciated as much of the original wiring may have been changed in the past 30 yrs by POs.

 

I agree that's as good a place as any to start. And, depending on what unfolds, I'd check for continuity through all those wires with the fuse links. Also, I'd check out that Accessory Relay. Not certain of it's function but my schematic has a wire (labelled Black/Yellow) coming off the starter relay, though a fuse link, into that relay, out of the relay as black wire and there to the IGN switch. Someone else may be able to offer some insight on that relay and how to test it.

 

I believe that relay is to allow the aux battery to supply the acc load when the ign switch is in the acc position. This would save the main battery for starting. A PO had even added a battery isolator in our truck to allow charging of both batteries off the alternator. We will likely rebuild to original when we get to that point. We are still tearing it down.