Have a '78 F-150, bought used from neighbor and trying to resurrect. Ran fine for me last year through the beginning of this one,. Had a charging problem and upon several alternators and some investigating figured it had something to do with the wiring (factory). Replaced the older frayed factory welded wirng set-up to the alternator with older non-frayed factory welded wiring. Please understand that the truck started and ran fine (although somewhat hot and might leave me sit) before pulling it up to garage for the changeover. Upon replacing the wiring truck would not start. She cranks , has spark and fuel but will not turn over which leaves the battery virtually dead after 15 sec. Would greatly appreciate any help offered. Have a Haynes , old and newer and schematics are vague when dealing with the factory weld. I feel something upon purchase was not connected properly and would rather not spend another $80 to replace regulator and brain box. Have diagram of existing wiring, Don't know how to post though so should anyone like to see ( I think quite diiferent from schematic) would be happy to send via e-mail or let me know how to post it. Connections from regulator going into the factory weld just don't make sense to me, almost creating a loop. Last time went to crank, cranked a bunch of times and then an audible pop! came from what I thought was the brain box. Never did that before while troubleshooting. Thought that it might be the ground wiring, there are several though don't understand why. Cleaned everything and replaced battery hook-ups. Have new regulator and b box but don't what to connect as if it's not wired properly, well you understand. Thought about just replacing whole harness but would really like to kick this one in the butt, very frustrated at this point and still feel it is something simple, so much so that I may have overlooked. Have new motor being built and need to inspect end of month. Any help is greatly appreciated.
Thanks, Brad

 

WOW!
Start at the battery. Give it a good charge and load test it. It ought to last longer than 15 seconds when cranking. Clean battery terminal posts and cable ends. Clean ground cable connection at the block with a wire brush to assure good contact.

Remove solenoid switch on passenger side inner fender well and wire brush the fender where it is attached to assure good ground. Battery positive cable connects to big post on solenoid switch closest to the battery. There is also a smaller wire attached to this post that goes to the fuse block and on to the ignition switch. It should have a fuse link in line near the solenoid switch. Probe the wire on the ignition switch side of the fuse link to assure the fuse link is not blown (pop you heard).

The large post facing the firewall on the solenoid switch connects to the starter with the longer battery cable. Check connections for cleanliness.

The "I" post on the solenoid switch goes to the coil battery (+) post and should have voltage to the coil with the ignition switch in the run position.

The "S" post on the solenoid switch goes to the neutral safety switch and is hot when the ignition switch is in crank position.

Your electronic ignition control module has two plugs with a total of six wires, two in one plug and four in the other. Have a parts store run a test on the box to assure it is good.

Looking at the wires coming out of the box:
The red wire in the two wire plug goes to a splice in the coil (+) to ignition switch wire.
The white wire goes to a splice in the starter solenoid "S" to ignition switch wire.

Four wire plug:
Green wire goes to the coil (-) post.
Black, violet and orange wires all go to the distributor connector at the distributor.

The wire colors in your wiring harness won't necessarilly match up with the colors of the wires that come out of the silver box. The wire colors mentioned above will orientate your harness wires to the correct connection when adherrance to the module wire colors is followed.

The alternator harness will have a wire on the "S" post on the back of the alternator (stator) to the "S" spade terminal on the voltage regulator.
There will be a wire from the batt post on the alternator to the "A" spade terminal on the voltage regulator and also a splice with a wire going to the fuse block on the firewall on to the ignition switch.
The field post on the alternator goes to the "F" spade terminal on the voltage regulator.
There is a ground post on the alternator that most of the time isn't used, but you can add a wire from that post to a ground if you would like.

That about wraps up the ignition and charging systems wiring. Check yours out to make sure everything is going where it should and re-post if you still have problems. It'll be easier to trouble shoot if you are positive that your wiring is routed correctly.

Check these diagrams, may be clearer than what you have:
http://www.autozone.com/servlet/UiBr...3d800ce982.jsp

 

You only need fuel, spark, and compression for the engine to run. You said you have fuel and spark. A nice blue spark? A few other cases when I have seen an engine have all the above, and still not start are the timing chain jumped(you can tell this because the engine does crank evenly) or the plugs where fouled.

Pull some of the plugs and see if they are wet with fuel or black. If so, they are fouled out. The best solution is get a new set of plugs, but you can try cleaning them with a wire brush, though this sometimes only helps a little bit. If you get new plugs, and it still won't run, pull the plugs again to see if they are wet with fuel. If they are, your float in the carb may be stuck with dirt from the fuel tank, flooding the engine with fuel.

 

hagapeach and Franklin2, thankyou for a prompt reply. Currently on the weekend shift so won't be able to chack anything out until Sat. nite at the earliest. For the most part (from memory) what hdgaperach had said about the wiring is correct; however there are wires coming off of the ones mentioned that don't seem to match with any schematic I've come across (will try web site mentioned later this even.) Battery is fresh and currently has nominal charge. When last pulled plug (only one) wasn't a usper spark, but one none the less and it was a bit wet, wouldn't say fouled but could be getting there, onlt about 3000K on them but engine is in need of overhaul. Running a Demon carb and fuel lines as well could be gunked (fuel in carb looks clean and getting a nice flow, maybe too much!) Is there a way to home-test the voltage regulator and module or is that a parts store check? If the later then will probably not be able to post verified reply until early next week. By the way, prior to first post I did clean ground connections with Dremel except for removing the solenoid. All fusible links are new except the one coming from the solenoid and the regulator, that one is original and tested fine at the junk yard (so I was told anyway). Will look over everything again tomorrow nite, Thankyou gentlemen for your input and will post again soon, Brad

 

There are two ways the alt can be wired. The first diagram is usually the way a truck is wired since most of them have factory amp guages.




If you have a "alt" light in the dash, then it's wired this way.

 

Per hdgapeach, checked and cleaned as per your suggestions. All seems ok (thanks for the detailed discription as well as the link). of note are a few wiring changes, not mine but as came with the vehicle. Coming from the front post of the starer solenoid is a black wire(fuse link) and continues onto a fact type connection that also has the yellow wire from the voltage regulator and a red wire from the battery line coming off of the alternator. The red wire is part of a factory connector that also has black and yellow wires(2) going into it from the factory weld in the black battery wire coming from the alternator. The factory weld also has another black wire going directly to the connection of the red, yellow and black wires under the fusible link from the starter solenoid. Stator wire goes directly into a factory connector(yellow wire) adn from that connection the red/green wire goes to the voltage regulator. Field wire goes straight to the voltage regulator, also had a black/grey wire spliced into it (I guess for the electric choke), but not in use, so taped up. Ground is not used. There is a ground wire coming staight off of the Neg. battery post and is connected to the fender well. Also of note is another wire with in-line fuse coming off of the front post of starter solenoid and going thru the fire wall, assume this goes to the fuse block and/or for the accessory gauge pack that was after market, amp meter does not work, maybe disconnected. Have about 13 volts at battery but only max at 6v at coil, could this be from bad module and or the voltage regulator? Also lost spark. Will replace plugs tomorrow and re-check. Should I replace coil? Could the distributor have anything amiss and needing attention? If wiring as stated can I hook up new module and voltage regulator after changing plugs without frying anything or do you suggest other action, new battery or replace coil? I had a weak spark before so don't know why I have none now, thought one of the boxes might be bad, plugs are pretty cheap anyway, old ones don't look bad but feel I'm running out of options before having it towed to the nearest electrical mechanic for what will probably be a simple solution. Should I be pulling all of the plugs or just one? I changed them at the beginning of the year, so only bothered checking easiest one to get to? Thanks again to both Franklin2 and yourself for all of the much needed help! Will post again soon, Brad