1966 Coupe DeVille Wiring, Engine/Idle Questions

[Aki]

Hello all, 1st time Cadillac owner here. My background is mostly injected, turbocharged Subaru racing so this is a whole new world to explore. I have to say, it's already a joy to work on these cars with how much room they have for activities!

I've done some searching around on here but have run across a few things where some direction would be helpful. I did pick up a FSM so can reference the wiring diagrams, etc. once I know what I'm looking at, or what might be missing.

Wiring:
I have found a few areas where it looks like some accessories might have been removed or previous modifications un-done. I suspect the car had some more aftermarket stereo equipment than still remains (deck and 2x door speakers). I found some very modern wire and an inline fuse holder near the battery, the other end of which terminates somewhere behind the dash. I found a loose ground terminal near the battery and said inline fuse. Also, right next to that ground and fuse is what looks like some stock wiring harness that's unplugged. It's right next to the alternator; unsure if related to the aftermarket stuff or not.

There is an aftermarket single DIN stereo in place and working in the car. There were a few loose wires next to it but coming from another part of the harness. Not sure if those were just attempts to intercept some switched power for the stereo or something else entirely. I know the cigarette lighter is inoperative and clipped, suspect the shortest of the three loose wires is possibly for that since it's nearby.

Next there is some melted wiring that's on the passenger side fender well in the engine bay. Looks like a factory plug. Maybe this car had AC at one time? I found no other evidence to suggest it had that option, just a guess based on location.

Right in front of the radiator/core support are a few factory blade connector ends that are unplugged, 3 total from what I can see. Might fit the AC theory if there was another fan here or sensors on the condenser?

Engine:
My friend took delivery of the the car so what follows was all second hand accounting, but it was driven about 500 miles to reach here, and on a pretty hot day. The oil had been changed before departure but was showing about 1-2 qt. low 100 miles from home, and the engine bay was coated with oil mist. It was topped up again and driven the rest of the way home without issue. Speaking with the previous owner they suggested it might have been a bad PCV valve (which fits if the crankcase was pressurized and pushed oil out the breather/fill tube).

We installed a new PCV valve, and I replaced the hose from the valley cover hard pipe to the valve since it was showing some cracks and was very leathery. The smaller 3/8" to 1/4" valve to carb hose was decent enough to reuse but does anyone know of a suitable new replacement? Parts store didn't know of one off the shelf with that reduction in size.

The idle when in Park or Neutral is quite high but seems fine when a gear is engaged. I've been reading that this can be vacuum leaks moreover than a carb tuning issue. I do wonder if there were PCV issues leading to poor idle and this was someones fix, or since this car was previously tuned at altitude in Colorado and is now much closer to sea level, could it indeed be a base idle adjustment issue? Still need to try capping off any vacuum line/port to check the carb for leaks but wanted to get other opinions. Was also curious if people had recommendations for tachometers, I could install a basic electrical or mechanical permanently one on the car, but is there a simple tacho just for testing that people like? It is also dieseling on shutoff, trying to snap the throttle closed quickly seems to help it shut down. I understand that high idle is a cause for dieseling though, so hoping one will address the other..

I also wanted to compression test the engine just to see how it's doing. I found the instructions for a 346ci, would the same steps apply to a 429? Would I need to point the fuel line in to a jug so I don't introduce any fuel in to the engine?
Sorry for the basic questions, just coming from a place where I'd disable the pump by laptop or unplug a controller 


We have some OEM replacement wheels coming from Coker, was curious is anyone else is running those and if they will needed a beauty ring to allow the stock hubcaps to attach. Have heard you need something like 1/2" of lip for them to grab on to.

I've included a few photos and can certainly take more if they'd help with diagnosing what's going on.
Thanks in advance for any advice you might have; it's great to see such an active forum in the days of social media!

Alex

[savemy67]

Hello Aki,

Regarding a compression test, generally the same procedures apply regardless of engine, as applied to carbureted engines.

Make sure your battery is fully charged.  Engine should be cold.  Remove all the spark plugs.  Block open the choke and throttle valves.  There is no need to disconnect the fuel line from the carburetor as the engine will not develop enough vacuum at cranking speed to draw fuel from the carburetor.  A properly operating carburetor float and needle valve will prevent excess fuel from entering the carb.  Do not pump the gas pedal when cranking.  You are not trying to start the car.  Be sure all of the plug wires are away from an accidental ground connection, or deliberately ground all of them in a safe manner.

Connect your compression tester to one cylinder, and crank the engine 4 to 6 times so the tester has a chance to obtain the highest reading.  Record the result, and do the remaining cylinders in turn.

The 429 should read around 180 to 190 pounds per cylinder.  The absolute number is not as important as the percentage of variation between cylinders.  If any of your cylinders vary by more than 10 percent, a squirt or two of oil into the cylinder, and a repeat of the test will help determine if you have a ring problem or a valve problem.  If the readings improve after the squirt of oil, your rings/cylinder may be worn.  If the readings do not improve after the squirt of oil, a low reading may indicate valve problems.

Respectfully submitted,

Christopher Winter

[The Tassie Devil(le)]

G'day Aki,

What a wiring mess.

But, nothing is unfixable, but you do need to get a Factory Shop Manual, as this will  be the best investment that will be made whilst you have the car to work on.

That first set of pictures looks like factory wiring, and the Manual will designate where they are from by looking at the colour-coding, grouping, and the second picture does look like it could be from an original 2-wire Alternator.

The under dash ones are typical of a rushed "want to get the stereo working NOW" episode.

Bruce.

[Aki]

Thank you so much Christopher and Bruce!

Should hopefully have time today to do the compression testing.

I did snag the Detroit Iron shop manual as well, so will dig in to that and sort out what's what for wiring.

[scotth3886]

Thank you so much Christopher and Bruce!

Should hopefully have time today to do the compression testing.

I did snag the Detroit Iron shop manual as well, so will dig in to that and sort out what's what for wiring.

I'm also a newbie very late in life starting with my first old Cadillac, incidentally, also a 66.  Had/have many many old Pontiacs though.

Although, horrifically old, I am quite computer literate and tried the Detroit Iron CD version of shop manuals.  Also been around OBD-II in late model cars with laptop in hand, BUT I find the best method for something like this ole beast is print.  The manuals I think come in handy are the:

Shop manual

https://www.ebay.com/itm/1966-Cadillac-OEM-Factory-Shop-Manual/262750597692?hash=item3d2d27f23c:g:Ps8AAOSwC~tdZgx6

Fisher body manual

https://www.ebay.com/itm/For-Chevy-Corvette-1966-Detroit-Iron-1966-Fisher-Body-Service-Manual/283567192913?fits=Year%3A1966%7CMake%3ACadillac&hash=item4205ebfb51:g:C6oAAOSwYTpdQwHQ

If you're going to do a dive deep then also:

Assembly manual (I had never looked at this one before so I can't attest to its helpfulness, but I did just now order one)

https://www.ebay.com/itm/1966-Cadillac-Written-Assembly-Manual-Deville-Eldorado-Calais-60-75-Fleetwood/161924750549?fits=Year%3A1966%7CMake%3ACadillac&hash=item25b3779cd5:g:1hQAAOSwSdZWeGaR

Master part book

https://www.ebay.com/itm/1965-1969-1970-1971-1972-CADILLAC-MASTER-PARTS-CATALOG-ORIGINAL-PARTS-BOOK/133433739194?hash=item1f114547ba:g:v1wAAOSwUF1dA1Jp

Hollander exchange manual

https://www.ebay.com/itm/HOLLANDER-INTERCHANGE-PARTS-MANUAL-HOLANDER-BOOK-1954-1966-CATALOGUE/324233228027?hash=item4b7dce6efb:g:bZYAAOSw~JBfEjjg

[Aki]

I agree on the print media, Scott! The shop manual you linked is the one I got a paper copy of from Rock Auto. Reprint by Detroit Iron of the original 1966 manual. Sometimes it's nice to have scans or other digital reference material but once you're coated in grease it's less fun to navigate anything on the computer, hehe.

Good news on the engine front! Compression test looks very healthy:

1 - 190
2 - 180
3 - 180
4 - 190
5 - 190
6 - 193
7 - 190
8 - 185

One surprise while doing that testing was that cylinder #2 has a different spark plug than all the others. They're all gapped equally to about 0.32 but 7 Autolite 85s and one lonely AC Delco R45S. Is that going to be an issue at all if they're still gapped the same?

I also removed the small section of wiring near the alt that had melted away and cleaned up a few other previous fixes that had since failed. Will now dig in to what exactly it was that let go...

[MikeLawson]

Given the current state of your wiring it might be worth considering obtaining an engine compartment wiring harness radio wiring from a parts car. This way, you'll have everything you'll need to restore the car back to its proper condition. I believe the engine wiring harness unplugs at the fire wall and the whole thing could be swapped out. If you got a replacement harness you could easily clean it up, make any needed repairs and then install it in your car.

[Daryl Chesterman]

Aki, in the second picture showing the alternator, the plug-in connector pictured by it is for the stock alternator.  The black wire with the eyelet is probably a ground, but you would have to check a wiring schematic to be sure, like Bruce suggested.  Someone has substituted a Delco 10si alternator and made up a plug-in for the internal voltage regulator.  The original alternator had parallel male spade connectors and looks like this (picture courtesy of Rock Auto):

https://www.rockauto.com/info/177/20169_BAC__ra_p.jpg



Has your original voltage regulator been by-passed?

Daryl Chesterman

[Aki]

Someone has substituted a Delco 10si alternator and made up a plug-in for the internal voltage regulator.

Has your original voltage regulator been by-passed?
Daryl Chesterman

It was bypassed with fire, it seems! Very astute observations, Daryl. And thank you for the additional info on the alternator. I had only a partial serial code on that unit to go from and wasn't finding much online.

So this makes more and more sense based on the additional heavier gauge wiring and inline fuse that was added after the fact. There is some kind of homebrew enclosure/box in the trunk which likely had a subwoofer in it. And the parcel tray sheet metal has been hacked up pretty fierce on one side, and no interior trim remains on or around it. There are two Pioneer speakers in the door cards but nothing further as far as speakers. I'm betting that whatever was on the parcel tray or trunk drew way more current than the OEM regulator could handle and cooked it. The new internally regulated alternator was installed and the old stuff just bypassed and left to hang. The melted section of harness is definitely what used to go to the now missing voltage regulator based on the wiring diagrams. The red output wire from the generator is the one that fried, took out the 3 wire plug at the regulator when it went. And that black wire is definitely the ground that ran from generator to reg.

Automotive archaeology at its finest, haha, every vehicle has a story but this one is getting pretty wild!

[fishnjim]

I'd say things look normal for one of these that's been around this long.     
My recommendation is always to take one system at a time.   Get that one right before the next.
So if you start with the wiring, assess what's "wrong" and what it'll takes to fix/replace, how to best accomplish that, cost, time, etc. you'll be way ahead of the pack.   
Then go through each system, as time and money allow, and it'll be ready to cruze safely again.   But if too slow, other things will start to show up at same time.   Enthusiasm wanes.   
Owners always get to a point where something fails and they have to decide whether to fix as is(?parts?) or adapt/change (parts) OR abandon the effort(no parts/costs too much-let sit) and that's how they get in this condition.   Little by little over time.  Someone else comes along and kicks it down the road they're own style.

[The Tassie Devil(le)]

I can't believe that anyone with the ability to change an Alternator and get the re-wiring done would simply leave the old wiring simply flopping around.   Even a short piece of electrical tape would suffice to hold everything up out of harms' way.

Bruce.

[Chuck Swanson]

I would highly recommend a new engine harness, as they are reproduced, along with a battery disconnect.  I have 6 of these (65-66) and always replace at least the engine harness when I get them. 

As a side note, my 20 yr old son drives a '65 Eldorado, and has an '04 Subaru...he has worked at Subaru dealer for over a year too Too bad not local as he would fix all the Cadillac issues as he knows these cars very well, and maybe would trade for help to convert his WRX to an STI . 

Use inner wheel weights only or special offset weights (not made anymore). 

Chuck 

[cadillacmike68]

I would highly recommend a new engine harness, as they are reproduced, along with a battery disconnect.  I have 6 of these (65-66) and always replace at least the engine harness when I get them. 

As a side note, my 20 yr old son drives a '65 Eldorado, and has an '04 Subaru...he has worked at Subaru dealer for over a year too Too bad not local as he would fix all the Cadillac issues as he knows these cars very well, and maybe would trade for help to convert his WRX to an STI . 

Use inner wheel weights only or special offset weights (not made anymore). 

Chuck

Who makes replacement harnesses for these years - 1965-70? I'm interested in one as well.

[Chuck Swanson]

A few vendors, but here is one:

http://www.wiringharness.com/PDFS/2020_Cadillac.pdf

YNZ does also

[scotth3886]

A few vendors, but here is one:

http://www.wiringharness.com/PDFS/2020_Cadillac.pdf

YNZ does also

Thanks.  That's who did my complete replacement 63 GP harness some 21 years ago and it's remained trouble free ever since.  Frankly, I wasn't having trouble with the original harness either, but the car had undisclosed frame rust (dealer purchase) so I took it completely apart, replaced frame (no VIN in frame), and did everything from the pavement up.  Fast way of turning a $20,000 purchase into a $100,000+ car.

[bcroe]

The idle when in Park or Neutral is quite high but seems fine when a gear is engaged.
Alex. 

Regarding the high idle, your car was built with a switch pitch
transmission, note 2 electrical connection on the left side.  The
intent is that the trans torque converter is put in high stall by
12V applied to the upper terminal, when idling in drive.  This lets
the engine idle easily without much load. 

If the above is not functioning, the trans may be in low stall when
idling in drive.  This would tend to load down the engine, so the
idle may have been raised to compensate.  In that case the idle
will be a lot higher in park, with the trans dis engaged.  Bruce Roe

[Aki]

Hehe, this is one of the more finished projects at the moment, if you'd believe it 
But I hear ya, dividing things in to chunks is definitely the way to go and to keep the fires lit.

And you said it, Bruce! Pretty tremendous lack of care shown, here. 

Chuck, thanks for that info! There were a few other spots on the harness where I was at least planning to re-wrap or protect a bit better, but that price is quite reasonable to have the whole thing done.
And hahaha, that would be something! I definitely know more about Subarus at this point, they're like Legos much of the time but not without their subtleties as well If he's got a WRX as a starting point that simplifies things tremendously, as wiring is usually the biggest chore (my race vehicle is an STi swapped 1st gen Legacy).

And very interesting bcroe, thank you, I will investigate that!