1976 Coup Les Prblemes Electroniques

[A.D.MunierDucdeCadillac]

Hello All,
I currently own a 1976 Coupe Deville that requires some cosmetic work. This includes the cabriolet top, the paint, and the interior. (To this end I am looking for the rubber bonded carpeted and embossed Floor mats in grey)

The cosmetic aren't the only issues that the car currently has. Under the hood there is a group of cut wires on the passenger side in the general area of the climate control components. I have no current idea what was removed or disconnected from this area. The Carburetor is aged well enough that its linkages don't seem to allow the flaps to open adequately enough that the car can run uninterrupted unless I prop them open with an appropriately proportioned implement. Furthermore the throttle must be revved prior to shutting the engine off, or it will not start up again. The current idle seems to be somewhat high if I tell the truth. Additionally I have a moderate leak between the engine and the transmission, and My windshield washer fluid reservoir is shattered.
I am of the mind that all of these issues can be simple enough adressed, so I worry very little about them.

However I have considerable concern about a perplexing light dimming and fluctuating phenomenon that happens in the cabin. Please note that I have a delco thermal limiter fuse and an oem gm blower motor relay in my possession ready to be installed. First, the electric seat control switch engages the motors somewhat jarringly, operates considerably slowly, and this switch whenever it is pressed dims the cabin lights without fail. Secondly the radio will not turn on unless you wheel the volume dial around delicately to find the single point in its radius that it coincides with an electrical current being supplied to the system, at which point there is a loud pop from what I presume is the speaker(s). This pop is the only sound they make or the system makes. If you tune, change band, or press presets, nothing at all occurs. But when this signal is established it has the added effect of engaging the motors of the seat controls for an instant. Essentially you feel the radio being powered through the seat of your pants. This may be something inconsequential but it is alarming to me. Additionally this also causes the lights in the cabin to flicker. I have an idea that the cut wires may be related to the next issue; the radio mast does not raise at all the button for the antenna illicits no response from the vehicle that I can discern. And all of this troubles me.

Now I defer to your collective experience and hope that I can be directed towards a simple solution and years of listening, lighting, seat sliding, antenna lifting pleasure.


A. Munier

[Scot Minesinger]

If you have not already, purchase a high quality battery disconnect (on negative), install it, and disengage whenever the car is off and unattended.

This reads like and electrical nightmare, and could be very simple to fix if only the exact problem(s) was known.  Unfortunately 1975 and 1976 (maybe other years too) Cadillac used very poor quality wiring harnesses.

Of course if you have not already, please purchase the Cadillac Factory 1976 shop manual and the Body by Fisher 1976 manual.  It will be difficult, but basically you need to interpret the wiring diagram and find the problem. 

Highly recommend you find the history on previous electrical repairs for this vehicle.  This may save a great deal of time.

How does it drive otherwise? 

[A.D.MunierDucdeCadillac]

Good Day Scot,

I thank you for objectively and informedly Dropping my heart into my Large intestine. The coupe drives like a train. Literally I don't get on the throttle much at all. I haven't replaced the resonator and muffler yet so I just get it started and let the car roll off generally which it does somewhat readily. But after that is said and done it steadily pics up pace. I rather enjoy the torque-ish-ness of the old girl.


I am goin to get my hands on those manuals in short order. then Off to all sorts of ulcer related hell. I am in love with this damned vehicle I can't lie to you. So I just have to call on the good spirits of automobillia, and get this right. I may try to acquire or actually restructure a full harness using a pegboard. (How would that affect resale value in the long run?)

As for the Cut off, would a quick disconnect work also?

A. Munier

[Scot Minesinger]

How you wire the Cadillac so long as it is done right (in compliance with industry manufacturing standards) and functions reliably without draining the battery should have no impact on the resale value. 

On the comment about it driving like a train, I could not really tell if that was good or bad?

[bcroe]

To fix a car like that, you or someone you hire needs to have studied the
art and understands troubleshooting.  Do not think that just changing parts
will be an easy fix.  So many just want to "see" the problem.  You must
use instruments to track down the problem, guessing has little chance. 

I have made some pretty scary harnesses, but I was in the phone
business.  For a car like this it is quite a challenge, and the opportunities
to screw it up are huge.  One big problem is getting the connectors, the
shops that specialize in this seem to have found them. 

Marginal problems like this are more difficult than hard failures.  Switches
or connectors may have too much resistance, without outright failure.  I
took the easy fix on antennas decades ago, there are no power ant here. 
Radios can be sent out and fixed, speakers debugged or replaced. 

Don't be surprised, if you discover the car once had fuel injection. 
good luck, Bruce Roe

[chrisntam]

Here's battery disconnect switch for both top & side terminal batteries.

https://www.amazon.com/Battery-Disconnect-Switch-Will-Both-Side/dp/B00099YOV8

[Scot Minesinger]

I know these are used all the time, but they are not that great.  I would use a real good "T" handle 900 amp "Flaming River" type that Summit (and others) sell.  The flaming river switch allows multiple ground connections, I have frame, body and engine grounds on the other side of my Flaming River negative switch.

[fishnjim]

You can tell a lot about how much work will be needed, by the odometer mileage, not mentioned, and how it's been stored or used since new.   I'd say by thumb '70s are in trouble over 70+K.   I gauge roughly 10K per decade - 50 - 50k, 60s - 60k, etc. because of the technology used in the day and years elapsed since new.   Collective vibration, corrosion, wear, and degradation takes a toll based on exposure hours.   I think this is the hardest part of this "hobby" that takes people in and sends them down the money rat hole all the time.   A quick look, fall in love w/ terms of endearment, like old girl, etc. are tells, but don't always realize what they're getting into.   Classic story.   
Usually, when somethings been disconnected, it's because the PO didn't want to spend the money to have it fixed or it sat and someone "pilfered" the parts.   It's usually "cheaper" to fix it in time than years later but that decision occurs in the transition between a "used" car and a "coollector" one.   People don't spend money on them after a certain period/$expenditure of owning.
The problem with electrical is you fix one thing then new stress causes something else to go, so at some point you have to repair/place it all because the deterioration leads to continual resistance build up.  It's a major job to go through a whole electrical system and repair and replace as required.   Best to do in conjunction with other repairs.   
One has to decide if they're preserving or restoring before jumping in.   Maybe best to just make it safe, drive it as is, and enjoy the "gremlins".   I've lived here 9+ years and a neighbor has a period other brand car that he drives everyday all day, and I'm continually amazed it's still looks good and is on the road, but they seem happier that way.   Eventually, they all clap out, but it'll be well used up by then.

["Cadillac Kid" Greg Surfas 15364]

Bonjour Duc.
I am guessing that "rides like a train" is a comparison to French trains and that is a compliment.

From your description it sounds like perhaps someone has "re-wired" some of the car's circuits.  In spite of previous comments regarding the 75's and 76's having poor quality wiring I have not found that to be true.  It is essentially all copper wiring with Packard (manufacturer) connectors, and if the car was not immersed in water the wiring is more than adequate.  There were a few changes in the circuitry in 1975 and often mechanics working on these cars early on did not understand the changes and modified the circuitry.

Regarding the cut wires  "near the Air Conditioning components". Can you be a little more specific, and can you take a couple of pictures and post them?
Regarding the radio I would leave this for last on the line of things to do and perhaps un-plug the power to the radio.  The only thing the radio switch (on/off/volume) should do is turn on the radio and through the radio raise the power antennae.  If you have the optional foot controlled "station finding" feature it is POSSIBLE that there are some bare wires under the carpet.
Regarding the seat, the dimming of the lights tells me that the motors are straining. A small dimming of the lights with the car not running and a low battery is "normal", but the described action of the seat seems to indicate that some clean up and lubrication of the seat tracks might be in order.
Get your shop manual, follow the wiring diagrams, one wire at a time on one device at a time.
Au revoir
Greg Surfas

[Scot Minesinger]

The 1975 and 1976 wiring harness have a weakness where the wires back out of the black connectors (especially the power wire on programmer connection behind glove box) when they are unplugged 40 years after manufacture and plugged back in.  In comparing the 1975 harness to a 1974 Cadillac wiring harness it is obvious the 1974 is better quality.  This may have been the wiring harness manufacturer cutting corners on Cadillac without telling them.  I have seen two replacement under dash (from factory, not aftermarket) wiring harness on 1976 Eldorados.  They replacements were very high quality. 

In fairness to Cadillac, yes they did not design their cars to last 50 years and to have the connectors unplugged and then reconnected multiple time either.  However, the replacement availability of much higher quality makes me think, they knew it was an issue back in the day.

[A.D.MunierDucdeCadillac]

Good Day All,

(forewarning this post is lengthy)

I haven't been near a computer to check the replies on this. I see that I have a lot to think through. But I am in good company.
As far as the confusion about my comparing the C.d'V. to a Train it was a remark made in pride. It pulls strong, it does feel smooth, and feels as though it applies its power effortlessly. I regard freight trains as highly capable machines, often under-celebrated for the level of engineering and durability that they benefit from being made with.

As far as this decision to acquire the car, I have to admit that it is a definite and irreversible choice to own and operate classic vehicles, to the exclusion of all others. I am currently also an owner of a panther platform sedan and am seriously thinking about turning that over to acquire a C-body GM to use as a daily driver. It's cheap, running, and the metal is cancer free. If it pans out, I will be chest deep in "seasoned" Detroit Metal. (I own a G body in addition)

I feel that making the investment to restore the wiring and connections at this point will only produce a benefit.
I do take into account that the actual science and theory of electronics/electrical wiring has to be considered. I also presume that Cadillac did this when they initially manufactured the vehicles (or this would have been a 5000lb kiln in short order), moreover  I presume that the good members of this forum and other interested enthusiasts have found out many of the overlooked issues that may have slipped through the cracks at GM. So I suspect that if I am attentive to the harness and I maintain the consistency of the gauge and the soundness of the connections, I can (with the help of added information and the manuals) indeed produce a reliable harness. (I will consult an automotive electrical professional or two during and before this-(all suggestions are welcomed)). Also I believe that the connections may be something that I can commission if not purchase replacements of outright, or with enough information I can find substitutes that function in the same fashion (remains to be seen I would guess).

All of that was to say. I'm not upset at all about the car, and I am proud to own it, and I will take the necessary time to correctly fabricate a replacement harness. However for now I will take this to a wiring specialist and see whether or not they can trace the issue(s) down. Fortunately I know a reliable technician and Ill ask them to find everything that is questionable and proceed from there. (And along the way chastise them appropriately for trying to milk blood from stones... etc.)

I may be an oddball here but I honestly have a distaste for modern cars. It could be that I have wanted these cars for so long that I can't consider others, or it may be that I enjoy the fact that they are distinct from today's vehicles. I think that if I need to pay 20,000 for a basic modern offering, or with some work and searching can invest that amount to have an impressive and satisfying (God save me , Reliable also) classic; I opt to have the latter. At the point which I'd have invested 100k (If I manage to do it prudently) then I can have an exceptional vehicle of my own. That is my take on the matter anyway. But I am glad that all of you have kept me from getting starry eyed and rose tinted about this.


Glad to be here good people. (pics of the cropped and possibly absconded compenents, the datatplate, and the foot well, soon to come)

A. Munier

[bcroe]

However for now I will take this to a wiring specialist and see whether or not they can trace the issue(s) down. Fortunately I know a reliable technician and Ill ask them to find everything that is questionable and proceed from there.

I may be an oddball here but I honestly have a distaste for modern cars.
A. Munier 

I would favor this plan.  After the questionable stuff is cured, I think
there will be no need for a new harness.  Here only individual wires are
likely to be upgraded.  Your taste in cars is close to mine.  Bruce Roe