Move dash wires = no start
 

Even though I finally have the 67 GMC 3500 running, I still have not completely fixed all the wiring issues. I have been fine-tooth combing the under dash wires, and the headlight and taillight ones as well since I bought it. I have fixed 99% of the wires that the squirrels had for lunch, and replaced any otherwise bad ones I have found. For the past several months I have been dealing with the sight of a mass of rainbow-spaghetti (wires) where the gauges will be installed soon.
But I have noticed an annoying problem ever since it has been running. If I move these dash wires, the truck (when the key is turned) mysteriously will turn over, but will not fire. The first time this happened, I moved the tangled mess back to where I had relocated it from and this fixed the issue. Whenever this happens, it also sometimes makes a the starter turn weakly, unless you mess with the ignition wires.
But today I started cleaning up the wiring mess by zip tying them together, and I must now figure out what the problem is, not the symptom. Any ideas from the electrical experts?

Re: Move dash wires = no start
 

This has taken an even worse turn. The engine will not even turn over now. There must be a loose ignition wire somewhere...

Re: Move dash wires = no start
 

Remove any zip ties you have installed...they may be hiding wires that have been chewed at by mice etc and being all tied up in a bundle will make it impossible to diagnose.

First thing to check is fusible link in system to see if its shorted out and burned up....

Then check battery voltage
Battery leads to starter tight
Battery ground clean and tight
Ground cable between engine and cab in place
Ground cable engine to chassis in place

Check these and report back...then we will get into the wiring system for the ignition and start circuits...

:chevy::chevy::chevy:

Re: Move dash wires = no start
 

Sounds like a bad ignition switch. Mine did the same thing before finally not working at all. New one fixed the problem.

Re: Move dash wires = no start
 

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Also check the neutral safety switch if it has one....

LockDoc

Re: Move dash wires = no start
 

Good point LocDoc....

Tell us where the wires that you would move and cause the issue are located.

This link is to a post on the Electrical forum this site, that will help you test the system for open circuits...including he location of the fusible link on early and late models...

http://67-72chevytrucks.com/vboard/s...d.php?t=676663

Let us know how you go...

:chevy::chevy::chevy:

Re: Move dash wires = no start
 

Here they are before I had fixed most of them. It is impossible to tell which one is the culprit. My vacation ends Sunday, so my time to fix this is short.

https://imagizer.imageshack.com/v2/8...922/SwUAZL.jpg

Re: Move dash wires = no start
 

It's not impossible at all. It's the purple one, and there's only one purple one! Easy!

Trace it back to where it joins the bulkhead and turns red then forward to the key and neutral safety. That's the whole thing. Test for power at key switch poles, let us know. If no power, suspect neutral safety, check that.

If power on ANY term then you should get power on the OUTPUT or CRANK terminal of the switch when turned.

Hmmmmmm.......????????
 

Here is what I have done today to track this down. I went through the under-dash wiring for the fourteen thousandth time, and they all appear good. I pulled the fuse box, and they all appear good. I checked the brand new battery with my voltmeter, and it tests fine. I checked my grounds, and they appear fine. I went to the parts store and bought a new ignition switch, and the truck still will not turn over. So I then started tracing the purple wire like davepl suggested, and found no neutral safety switch (floor standard shift). The purple wire at the ignition had no power when I used the voltmeter.
But I found these:

Suspect # 1 Near the carb. A ground wire of some type?

https://imagizer.imageshack.com/v2/8...924/ZKCS1x.jpg

Suspect # 2 These wires ended at the starter, and the frayed one was barely holding on to it by only a few strands. I was able to rip it loose with my hand. Best suspect I think. The other wire was not attached to anything. My old pre-HEI coil wire perhaps?

https://imagizer.imageshack.com/v2/8...921/nozt2A.jpg

I may have to remove the starter to reattach this wire because I tried everything short of being a contortionist to get to where it attaches.
What puzzles me is what this frayed wire has to do with me moving dash wires around, THEN having starting issues. A coincidence perhaps....?

The mystery deepens...
 

Ok, I managed to get the red wire reattached to my starter with a new connector. Tried to start it and STILL nothing. I was thinking that maybe the starter has gone bad, but then I noticed that my headlights are not working now.
This truck has managed to go from running strong, all the way back to square one to when I bought it and NOTHING on it worked.
Before this happened it was acting up, but I got it started. It ran for a few minutes, then mysteriously died, and since then it will not even pretend to start. No turning over, not so much as a single "click" when the ignition is engaged. :cuss: :banghead:

Re: Move dash wires = no start
 

I assume you have checked both the positive and negative connections on the battery? Also the ground wire from the battery? About 2 weeks ago mine was giving me trouble and it turned out to be the negative battery cable had loosened up.

Re: Move dash wires = no start
 

Yes, and I rechecked them just to be sure. I even tried to use jumper cables to get SOME kind of electrical response (starter, lights, etc) but still NOTHING.

Re: Move dash wires = no start
 

Two related, things, which may not be the cause, having heard all the "starts" and "no starts"
1. In the engine compartment, in the area of the headlights (there's one on both sides) are in line fuse holders. They look lie rubber blobs or a wad of electrical tape on a wire. Inside the are short glass fuses. If blown, the p/u will NOT start.

2. In the engine compartment where the engine wire harness plugs into the fire wall (I may have mentioned this before, maybe not to you...). Unplug the harness, look closely to see if one of the connections has melted the plastic plug around it......

Number 2 problem can be intermittent, and kill the engine, any time...

Re: Move dash wires = no start
 

The two 4 amp fuses control whether the amp gauge works or not. They do not have anything to do with the whether the engine starts or not. The fusible link from the battery to the junction block on the inside of the fender will cause no power at the fuse box if it is blown or melted..... That's a good thing to check.

LockDoc

Frustrated
 

I am beginning to think that the brand new battery is the culprit. But my jumper wire attempt failed, so that is unlikely. It shows that it has power.

Re: Move dash wires = no start
 

Most parts stores can test your starter. Even though they can test it, it's not always an indication of whether or not the starter will function properly on the engine....
They can load test the battery, also, that's a pretty good indication on the battery....

Thanks, Leon. My fuses caused me some grief, been, too long ago.

HBTS, do you have a test light?

Re: Move dash wires = no start
 

I have one somewhere. But right now my voltmeter is getting a run for its money!
Whatever is causing this is some sort of complete electrical failure. I have started to unwrap the electrical tape from the under-hood wiring now. I expect to find a burned wire hidden somewhere. I have now removed the fuse box (considering replacing it due to rust) and the bulkhead. No melted connectors.

Re: Move dash wires = no start
 

Did you check for voltage at the alternator? It should go from the battery, through the fusible link, to that taped-up splice and from there directly to the alternator.

Re: Move dash wires = no start
 

Could I make a suggestion here....

The attached image shows the wiring on a typical Chevy starter motor....shown on the rear of the solenoid

There are three electrical cables on the solenoid...the large cable n the center is the battery cable coming down from the junction block,,,lets say that cable is at 12 o'clock....

Located at approx 3 o'clock is the Start wire that comes down from the ignition switch start terminal....(dont worry about the one at 9 o'clock right now)

Measure the voltage present at the main cable 12 o'clock...it should be 12 v...regardless of whether ign is on or not.

If it measures 12 v...move to next step....if it doesnt show 12 v go back to the junction block and test voltage at both terminals...they should both show 12 volts.

With the ign switch turned off...Take a small jumper lead powered from the battery positive terminal and touch it to the terminal on the solenoid at 3o'clock position....if the solenoid engages the starter should crank the engine.
If the solenoid engages (click sound) but the starter does not turn the engine, the starter or solenoid is most likely faulty.

If solenoid and starter work correctly using the short jumper lead, there is an issue between the ignition switch feed or the switch itself...

You mentioned a scenario where moving the wires would cause the starter to crank but the engine not start...I suspect the feed wire down to the solenoid is receiving a 12 volt cross feed from another wire...most likely due to chafing...

If the solenoid has failed...Amazon has them under https://www.amazon.com/Tru-Tech-SS20...t%3Ac10+pickup

or try your local parts store...most folk tend to replace the starter unit...your choice

Hope this helps...Bill

:chevy::chevy::chevy:

Re: Move dash wires = no start
 

Just did it. It has power.

Re: Move dash wires = no start
 

I appreciate the help! I will try that tomorrow in the daylight.

Re: Move dash wires = no start
 

Just make sure the ignition switch is Off when you try the jumper lead...

Ya dont want that old chevy starting while you have your hands in there...

Have fun

:chevy::chevy::chevy:

**update**
 

Today I went under the hood and unwrapped the electrical tape from the wiring harnesses. I also checked a fusible link that I found a on a black wire with a white stripe, and it was intact. So far I have not found any burned ones, so I will check the starter and solenoid when I have the opportunity. But the starter and solenoid possibly being bad still does not explain why the headlights stopped working.

Re: Move dash wires = no start
 

The headlight power feed, and the majority of the rest of the power feeds originate at the junction post on the fender.

Follow the positive cable from the battery positive post around to a plastic looking junction box on the inner fender...

Post us a pic of the inner passenger fender near the battery showing both of the battery leads...

It is possible your truck has been modified previously...it may have a battery cable direct to the starter solenoid and a smaller gauge wire on the positive battery clamp thru a fusible link, then to a smaller junction post on the fender...

If yours is the second style described, the loss of everything could be as simple as a bad connector on the positive battery lead....

Post a pic and we can see how its wired.

:chevy::chevy::chevy:

Re: Move dash wires = no start
 

I will post a pic hopefully tomorrow. More info for you. When I bought this truck there was no junction block at all, and no lights worked. I bought a 67 Chevy front end that had the lighting wiring harness, so I removed and installed it in my GMC. I also removed the plastic junction box that came with the Chevy front end and installed it with this wiring harness in the GMC. I hooked up the ignition wire, and put a fusible link in it. This is when the headlights started working.
And later I got it running.
But all that has been erased, and I hope we soon figure out why, because my frustration is at an all time high.