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Discussion Starter #1
Warming the truck up today it suddenly switched off. No power into the cab, no lights, blinkers or flashers.

Wiggled some underhood wiring and it worked for a moment....

Found a disconned wire down on the pass side fenderwell and reconnected it, no change. Swaped voltage reg, no change.

Truck has lots of wiring hacked on it for many years, but I am wondering what I am missing here... Should be one wire headed into the cab to power everything, correct?

Also, what does the three pronged unit on the fenderwell do? It has three tabs in a triangular array, and it is bolted on near the starter solenoid. It has power in one wire, but not any of the other wires.

Truck is set up for duel batteries with a battery isolater... Alternator is wired into the isolater.

any ideas? Just wanted to save some time before jumping into a bunch of diagrams.
 

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Fork over the $20 for a Haynes manual, grab your volt meter and start hunting. it is a pain in the ass, nobody (in their right mind) llikes doing it, but dedicate a couple of hours and you will have it figured out. Having a few cold beers on hand makes the process more tolerable.
 

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Discussion Starter #5
Fork over the $20 for a Haynes manual, grab your volt meter and start hunting. it is a pain in the ass, nobody (in their right mind) llikes doing it, but dedicate a couple of hours and you will have it figured out. Having a few cold beers on hand makes the process more tolerable.
Yeah, yeah. I have the manual, I was just hoping someone had run into the issue before and had a place for me to start from.
 

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Hawk - from the BAT terminal of the starter relay (fender solenoid) should be a fat BLK/YEL wire through the firewall. This wire splits under-dash into:

  • smaller BLK/YEL to the fuse box
  • BLK/ORG to the headlamp switch
  • YEL to the ignition switch.
Depending on what is dead, you can determine if it's the primary source wire or one of the feeds off the splice. Fortunately, that's as far as the primary power wiring goes. Should take just a few minutes to hunt that gremlin down and mercilessly kill it. Let's see gremlin guts.
:D
David
 

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Discussion Starter #7
Hawk - from the BAT terminal of the starter relay (fender solenoid) should be a fat BLK/YEL wire through the firewall. This wire splits under-dash into:

  • smaller BLK/YEL to the fuse box
  • BLK/ORG to the headlamp switch
  • YEL to the ignition switch.
Depending on what is dead, you can determine if it's the primary source wire or one of the feeds off the splice. Fortunately, that's as far as the primary power wiring goes. Should take just a few minutes to hunt that gremlin down and mercilessly kill it. Let's see gremlin guts.
:D
David

AWESOME. Just what I needed. thank you my good man! I will share in the feast with you XP
 

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Fork over the $20 for a Haynes manual, grab your volt meter and start hunting. it is a pain in the ass, nobody (in their right mind) llikes doing it, but dedicate a couple of hours and you will have it figured out. Having a few cold beers on hand makes the process more tolerable.
having the beer and let others dov the thinking is the norm.
openging the book takes to much effort
 

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Well, I sort-of handed you the direction to go, but if learning troubleshooting diagnostics for anything (engines, vibrations, etc. - but in this case electrical), then you need to stop and analyze what is or is not happening to cause the exact symptoms you are looking at. A logic tree of sorts, even if only in your head. Detectives solve cases using clues. This is the same, but using available symptoms as clues, then diagnostic results as more clues. Gather as many clues as possible to make diagnostics faster and easier.

In this case, let's say you lost power in just one circuit as shown in my first drawing below. What is the common denominator? Only component 2 is dead, though other components are fed from the same primary power feed and they are OK. This would indicate the primary power feed is OK, and that the failure is somewhere between the pink X and the orange X. I would begin probing for the break in the circuit in one section at a time, e.g. - from before the red wire splice to the component, then across the component, then from the component to past the ground. You don't need a diagram to do this, but it helps know what is beyond what you can see laying under the dash, or before you even start looking.

In the second drawing, we have multiple failures. What is the common denominator? Well, none of them are getting power, making the common failure point in the primary power feed. Therefore, we would look between the pink X and the orange X.

What else is common? They have separate grounds, but share a common primary ground near the battery. So, we should also check between the pink X and the blue X, including the battery. The entire circuit is necessary to function, and so every part of it should be considered in the analysis, including the battery itself. This way you miss nothing.

While some individual components may have issues, we will not check them at this point until we solve the common issue. Then we can move on to other trouble sections as the system comes online in chunks. It is possible you could have both situations below, but obviously we would start with the primary failure first, and that will make the secondary failure immediately apparent.

One final observation - our old cars tend to have more ground issues than power issues due to age and corrosion affecting grounds to a greater degree. However, if creating or following a troubleshooting plan, nothing is left out so nothing is overlooked. While not always possible, a majority of the time troubleshooting diagnostics will identify the failure specifically and allow going straight to the issue. This saves a surprising amount of time, money and frustration. HTH

David

Failure in one branch circuit:


A failure common to multiple devices, indicating a primary failure on either end of the circuits:
 

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There is also no shame in learning from others.
see the above post by David, the very first part he said what You must do.

Davids first post was info you could get by opening a manual.

you are correct-no shame in learning from others , thats only if you put effort in and hit your limit . you got a manual- use it first
 

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Discussion Starter #12
Thank you david! I usually use a logic like that, but the wiring is excessively modified and I have three red, large gauge wires taped into the harness that go into the cab, and a small tangle of stock wiring spliced in to make the alternator work... other than the little bit of stock wiring not much is left... I love it when someone uses all the same color wires to 'fix' their old harness...

After about an hour of digging around in that mess trying to find the cab power wire I called it a day. lol. I will have to see if any of the other stock wiring survives.
 

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Discussion Starter #14
took another look today, traced some wires and found out the amp meter that was wired in series had gone bad and cut all power from the battery.
 

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Excellent. That shows the value of logical tracing, and/or having a wiring diagram with that info. The diagram I peeked at did not have an ammeter, but it's pretty obvious when crawling in there where the power flows. Be careful - if you get good at electrical troubleshooting, you may find yourself making a lot of money. ;) Maybe 1 in 1000 people are not afraid of wiring. Perhaps 1/10th of those can actually do effective troubleshooting on it. It is a rare skill in high demand.

David
 

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I know this is an old thread, but I joined this forum just to say THANK YOU. I've been banging my head against the wall for three days and turns out I had the same exact problem - some genius rewired the truck without any inline fuses and the ammeter fried. ?
 
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