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  #1  
Old January 2nd, 2023, 07:15 PM
MeganK MeganK is offline
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Default Ignition Mystery

First and Foremost thank you all that have helped a new owner sift through some basic questions.

I have had my 66 for about a month now and I have done everything I feel I needed to do to see if I can get it running.

When I bought the truck the seller turned on the key, lights went on and we cranked the engine... just for a second or 2....

I get in the truck for that moment of truth turn the key on and nothing... no lights on the dash no power. I checked the battery, battery cables, connection at the starter and all were getting power.

I did nothing with this part of the system and now nothing. The only thing I had done in the cab was to replace the aftermarket steering wheel with the original. So out of desperation I changed it back to the crappy aftermarket wheel. turned the key, dash lights up. engine cranks...but I only cranked it for a couple seconds to get gas and oil into the system. I go to crank it a second time and no lights no power all over again.

In my head it seems illogical that this issue would be tied to the steering wheel/column so my next guess would be to start looking at the ignition switch wiring. Ignition wiring and diagnosis is a notch above my skill set and the previous owner seems to have had a passion for electrical tape and leaving wires to nowhere.

I am not sure if having the 500CI Cadillac motor and TH400 transmission adds to the complexity or not but I feel like it shouldn't matter. FYI I was able to narrow down the engine to a 1973 but without taking it apart I still don't know if it is a 472 or 500.

Not sure if i should invest in some kind of remote starter switch or fix what will eventually need to be fixed anyway.


thanks all

Megan
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  #2  
Old January 2nd, 2023, 07:29 PM
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AZKen AZKen is offline
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Default Re: Ignition Mystery

Hi Megan I'm sure I can help you. It all depends on if you monitor your post and answer in a timely manner.
1. When you say replaced steering wheel, do you actually mean just the wheel that is held on with one big nut or do you mean the whole steering column?
2. Does the cad motor have HEI or points ignition.
3. I do have some suggestions after I get these answered.
Right now it points to a simple battery connection. Focus on the two big battery cables. The positive and the negative. Clean the battery posts and the cable clamps. Tighten the clamps. Then, on the other ends, check and tighten the one to the starter. Then clean the ground, shine up the ground terminal on the cable and shine up the place on the motor where the ground cable is attached. Shine= to bare metal.
ALSO!!!!!!!! Check the voltage on the battery and report all findings.

Checking to see that "all things are getting power" does not catch a bad connection under cranking load. Does not catch a bad battery breaking down under crank load. So redo the check and clean and tighten again and be SURE TO CHECK THE BATTERY ITSELF FOR VOLTAGE> NEEDS TO BE 12.6V approx.
You MUST be sure of connections and battery before we move on to further troubleshooting. This is critical.

Last edited by AZKen; January 2nd, 2023 at 07:39 PM.
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  #3  
Old January 2nd, 2023, 07:33 PM
MeganK MeganK is offline
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Default Re: Ignition Mystery

the only thing i did was replace the steering wheel itself nothing with the column or shifter or anything. When i put the crappy steering wheel back on it worked but only once..

It has a coil. I checked the voltage at the battery 12.5 and at the starter 12.3 so i am leaning towards something in the cab being off...
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  #4  
Old January 2nd, 2023, 07:41 PM
MeganK MeganK is offline
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Default Re: Ignition Mystery

this was the original engine pic.. it is cleaner now LOL

PXL_20221130_180517196.jpg
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  #5  
Old January 2nd, 2023, 08:37 PM
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Default Re: Ignition Mystery

Well this website is not for GMC's with Cadillac motors but if it's an electrical problem maybe we can help.
Let me know when you have redone the connection cleaning and tightening.

The change if the wheel has no bearing on your issue. As you say there are many possibilities for your trouble, but first things first.

You have an intermittent electrical issue it seems. That usually spells connections. When the whole system is dead.... it spells big connections. So focus, clean and tighten the ones I mention again more carefully.

The very next thing is take battery to get it tested under load. Tell us what they say about the battery.

If you want to get a remote starter switch or jump the starter, go ahead. This will eliminate or expose ignition switch and wiring.
Do another check: Key off, turn on headlight switch to see if they come on. If they do, turn key on and crank motor, observe what the headlights do.....dim a little or go off? Did starter crank motor? Headlights won't come on at all?

Last edited by AZKen; January 2nd, 2023 at 09:07 PM.
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  #6  
Old January 3rd, 2023, 04:40 PM
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Default Re: Ignition Mystery

I would agree with azken, check battery connections. Check at the terminal itself and check where cable goes into terminal. If the terminal uses bolts to clamp down on the cable that is very often the problem.
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Old January 5th, 2023, 06:02 PM
MeganK MeganK is offline
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Default Re: Ignition Mystery

Update,, of sorts...

Did all those things.

used a volt meter to check battery, solenoid and everything else. made sure all connections were tight and clean and nothing..

then yesterday it decided to work again so i am going to rewire the ignition and clean up the rats nest of wires that are currently there

honestly I want to rewire the entire truck since god only knows how creative the previous owner was. Is there such a thing as a full wiring harness or do i need to make my own sections

Last edited by MeganK; January 5th, 2023 at 06:13 PM.
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  #8  
Old January 5th, 2023, 07:23 PM
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Default Re: Ignition Mystery

OK I will forget about helping with the troubleshooting part and just answer the harness part.

There are wiring harnesses. I use universal, pre wired fuse panel type. Some crimping involved. About $200.
Example: Click

A near "plug and play" type is about $600 for 63-66 Chevy. There are a few differences on GMC not covered. But that's OK.

Building your own is not viable.

This post should be in the electrical forum.

Last edited by AZKen; January 5th, 2023 at 07:50 PM.
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  #9  
Old January 6th, 2023, 12:06 AM
lizziemeister'sV6 lizziemeister'sV6 is offline
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Default Re: Ignition Mystery

Before I would just replace the complete truck wiring which is a major feat to accomplish since there are NO GMC specific harnesses available I would start with only the ignition circuit and see if you can get the truck to start every time you try. Just wire up a simple stand-a-alone harness to get it going and gradually go from there - You are already in a bad place cause the original motor/transmission has been replaced with a off breed donor engine - wonder why they used that motor/transmission combo but I guess they had it sitting around and said "Why not". Start with little accomplishments and once you gain a little experience and feel warm and fuzzy about it then go into tackling the prior owners cluster of a mess. I have seen many project cars and trucks abandoned and left for scrap because the new owner didn't have the knowledge, mental drive or the funds to finish. You can do it! Ever heard the old saying - "How do you eat an elephant? ----- one bite at a time."
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  #10  
Old January 6th, 2023, 01:52 AM
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Default Re: Ignition Mystery

I am pretty sure there is not enough difference in the "plug and play" harness to be concerned about.......and the universal harness is universal.

The only significant difference is the circular connector on the cluster printed wiring board.
You do not want to damage that!!!!! Leave it alone and plugged in.

The motor wiring is also not an issue.

It's not too challenging technically on old trucks, just a bit of work.. Satisfying DIY project.

There are ads on craigslist for helping you with installing harnesses. For a small fee.

Last edited by AZKen; January 6th, 2023 at 02:03 AM.
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