Sorry I'm new here so if I sound dumb that's why. I have an 1985 f150, carburatored, manual 4x4. I'm fairly mechanically inclined but wiring throws me off. I can't seem to get power anywhere. I checked all the fusable links and they are good, battery is charged. I have voltage at all the grounding spots in the engine compartment. I pulled the wiring harness off the ecm and I have power coming to it. I have power going from that harness to the fuse box. I put in a new ignition switch. I cannot get power to anything though, no lights, horn, blinkers let alone the starter. Could the ecm be faulty? Is there a way to test it? Could it be something else? I can jump the selenoid to turn over the starter. I appreciate your expert opinions. Thank you for taking the time to read and respond.

 

That's common - most people have a hard time understanding electricity.Exactly where & how are you checking?Exactly how did you check them? Click this & read the caption:


(phone app link)That's confusing... Voltage is measured BETWEEN two points; not AT one point. So it matters where each of the meter probes is. And it matters WHAT the voltage is; 0.007 VDC is "voltage", but it's not significant (effectively 0). For each thing you want to check, you have to specify the location of each probe for us to understand what you're checking, and what the reading actually means. Generally, the best place to keep the black probe is at a clean (shiny) spot on the battery (-) post. That's the standard reference point for measuring all voltage on a vehicle. Click this & read the caption:


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If you actually got ~12VDC between the battery (-) and the underhood grounds, it would mean that the main body ground is disconnected (or broken, corroded...).


(phone app link)I assume you mean "connector":


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The "harness" is the wiring bundle wrapped all over the vehicle, like the leather harness on a horse:


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Probing the EEC connector terminals is risky because they have to make good contact to the EEC pins, and the meter probe can bend the terminals so they DON'T make good contact.Why, exactly? When (before this symptom appeared, or after)? What brand/PN/source? Did you keep the original? Did the replacement pass the same tests that the original failed? I recommend you put the original back in, and don't change any parts unless they fail a published diagnostic procedure. Do you have a Haynes manual?


(phone app link)That suggests a problem AT the battery terminals. Read all the captions in this album:


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...and these:


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(phone app link)Of course, but it CAN'T cause any of the symptoms you've described.In the truck is the best way.Of course, and since the EEC can't cause any of the truck's symptoms, there MUST be some other problems (which isn't surprising on an antique pickup).So you HAVE voltage at the starter relay (it's not a solenoid).


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That suggests that the battery terminals are in good-enough condition to power anything else on the truck. The starter draws the most current, so the headlights & radio should work. The difference is that the starter is served by the block ground (main battery negative cable) and the headlights & radio rely on the BODY ground, which is a separate cable from the engine to the firewall sheet metal).

 

Steve83

Thank you for the very detailed response. I will try to answer your questions as best as I can.

Exactly where & how are you checking?Exactly how did you check them?

I tested the fusable links by cutting the wire after the link and testing the voltage by using a voltmeter and having one lead on the battery and the other on the wire. I then used butt connectors to repair the wire.


That's confusing... Voltage is measured BETWEEN two points; not AT one point. So it matters where each of the meter probes is. And it matters WHAT the voltage is; 0.007 VDC is "voltage", but it's not significant (effectively 0). For each thing you want to check, you have to specify the location of each probe for us to understand what you're checking, and what the reading actually means. Generally, the best place to keep the black probe is at a clean (shiny) spot on the battery (-) post. That's the standard reference point for measuring all voltage on a vehicle.

I measured the voltage at all the grounding points I could find by by using a voltmeter and having one lead on the battery and the other on the ground point. I believe I got 12V at each connection. I will have to double check those.

If you actually got ~12VDC between the battery (-) and the underhood grounds, it would mean that the main body ground is disconnected (or broken, corroded...).


(phone app link)I assume you mean "connector":



Probing the EEC connector terminals is risky because they have to make good contact to the EEC pins, and the meter probe can bend the terminals so they DON'T make good contact.
Yes, I removed the connector and probed the terminal with my voltmeter and observed varying voltages in the connector. Not all had 12V. I found 2 spots that had 12V reading between them, then kept one probe on one of the spots and probed the other spots to measure the voltage. I then measured the voltage from the one spot to the fuse panel. Some spots int eh fuse panel had a 12v reading others were less. Should they all read 12V? Sorry if that sounds confusing, it makes sense in my head.

Why, exactly? When (before this symptom appeared, or after)? What brand/PN/source? Did you keep the original? Did the replacement pass the same tests that the original failed? I recommend you put the original back in, and don't change any parts unless they fail a published diagnostic procedure.

Since nothing worked when I turned the key I assumed it may be a problem with the switch, I purchased one from my local auto parts store. I do still have the original. I do not know what diagnostics to run on it to see if it is faulty.

Do you have a Haynes manual?

Yes I have the blue version.


That suggests a problem AT the battery terminals. Read all the captions in this album:

The terminals look ok, no corrosion, posts are clean. I did replace the heavy gauge wire from the negative terminal to the starter.






(Of course, but it CAN'T cause any of the symptoms you've described.In the truck is the best way.Of course, and since the EEC can't cause any of the truck's symptoms, there MUST be some other problems (which isn't surprising on an antique pickup).
That is good to know that that is not the problem.

So you HAVE voltage at the starter relay (it's not a solenoid).

Yes I have 12v at the relay and can get the starter to turn by jumping the relay.




That suggests that the battery terminals are in good-enough condition to power anything else on the truck. The starter draws the most current, so the headlights & radio should work. The difference is that the starter is served by the block ground (main battery negative cable) and the headlights & radio rely on the BODY ground, which is a separate cable from the engine to the firewall sheet metal).[/QUOTE]

I will look to try and find all the body grounds and ensure they have a clean surface.
How many body ground points are there?

Thanks again for your help.

 

Don't do that any more. Even if you're really-good at crimping, it's unnecessary damage to the wires, and a very high risk of creating new problems in the harness. Either use a common stickpin or a commercial pierce-probe to check at a point in an insulated wire, as linked in this caption:


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But it's generally good enough to check at the ends of a wire (even a spliced wire, like those with fusible links). A stickpin or commercial back-probe is usually sufficient.WHICH lead? On WHICH battery post? Be specific. If you can't remember clearly & specifically, re-check more carefully, taking specific notes &/or pics.That's very vague, and not conclusive at all. Keep the meter's black probe on the battery (-) post. If that's not possible, measure voltage to another true grounding point. If it shows 0V under all conditions (key on/off; headlights on/off; cranking...), then it can be considered equivalent to the post, and you can move the black probe to it. But you started with a dozen unknowns; randomly chose 2 unknowns; and then randomly chose one of those as a reference to check other unknowns.Read the Haynes; cover-to-cover at least once so you know what's in it, and where to find things when you need to. I also like to cross out sections & pics that DON'T apply to my truck using a light-colored crayon (so I can still read through the marks if necessary). Don't use a highlighter - it will bleed through the pages.Read that caption - there are at least 2 distinct editions with the same blue cover.Does that mean you disassembled them and inspected everything? Or do you just mean glancing at them when you open the hood?When? With what? Why - what test did the original fail? Did you clean the mounting point on the starter down to shiny metal?Depends on what options the truck has - potentially DOZENS, but at least a dozen.

It will help if you put ALL the truck's details into your signature so we can see them all as we try to answer your questions, without having to dig back through the thread to see if you posted them and where.


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