Expert: Rob Painter - 2/23/2011

Question
QUESTION: Hello,
I recently purchased a 1981 cadillac coupe deville.It ran okay at 1st but now the heater comes on when the car starts and won't shut off,and the interior lights won't turn off either.Any advice?
Thank you!

ANSWER: Hello,

These were notorious for bad relay modules located under the hood on the passenger. Side at the plenum. They were bout $300 bucks and haven't been at the dealer for 20 years.

I have intruction for bypass with will only give you high or nothing, but I won't be back home for a couple days.

As for your dome issue, could be a bad pin switch where the door opens at the front.

---------- FOLLOW-UP ----------

QUESTION: Mr Painter,
Im interested in bypassing the heater blower when your back around. And was also wondering why else my interior lights go on and off at their own will as i don't think the doorpin switch is bad?Thanks again!

Answer
Hello,


I hope you appreciate this. I gave you very detailed instructions from scratch for your blower motor bypass. Did not have other computer. You will see I know a heck of lot about the Eldos. This should be the good engine the 368 CU in 4-6-8. Always disconnected the wire and ran 8 cylinder. I also list the problems with the 1982 and up with the aluminum engine. Your 368 is the last of the really good cast iron engines.

There are many issues that could cause the dome light problem and the pin is the easiest to check.

I have had many of these cars. Sold my 83 when I moved to Texas in 2009 and brought my Allante down instead of the Eldo.

I do not know if they go that old, but 85 will be pretty much the same. Go to http://www.alldata.com and check their chart. If they go back as far as 1985 or older that would be great. Seville will help you 79-85 as well.

If they have the cars listed, pay the $30 for membership. Download all the factory service manuals. For you, this would be gold! I make no money referring this site. Its just excellent for diagnoses.

I remember a module that controlled the dome light and if it has the factory alarm and illuminated door locks, could be a trouble there too.

I worked on these cars when new. I repaired hundreds of these from theft. The biggest problem is that there are things about these cars I remember and there are tings that if I look at a manual it jars my memory. It's just too darn long.

The heater blower resister module was such a big problem that at any given time walking through a service area and you would see two or three with their hood up and the module being changed.

These were a great car, but the common problems were loose steering columns from hanging on them to get in or out. By the way, always remember me for steering column issues. I still rebuild them for whatever problem.

Another very common bunch of issues with the HT 4100. Many have a factory built in knock commonly from rist pins and annoying, but generally will run for a long time.

This aluminum engine can never be run hot!!! If you hit 220 degrees your engine is self destructing and the first affect (not the cause) is a blown head gasket at minimum and it goes down hill from there real quick!!!

I get many people that thought, well I can at least drive it another mile. No you can't! Junk yard engines were commonly overheated and junk. If you can get an engine from Cadillac it will set you back $5K installed. I never had a problem with any of these engines other than the knock in a couple. I have owned over 20 Cadillacs, primarily the Eldos like yours, Engine is powerful and good on gas.

You would have loved my black 83 Biaritz with the grill, the trues,vouges and instead of gold, it was all chrome. Spent $5k just on the paint! Had it too perfect and when I was in Colorado, instead of driving her brand new Firebird convertible or the Corvette, she took my Eldo one night with her girlfriend and crashed it! That's one of many reasons she is an ex-wife!!

The digital radio numbers would not work right on these cars and if a Bose, they were very expensive to fix!

Power antennas had problems, either they kept running or the mast would break off. Cadillac used to stock mast kits which were a heck of a lot easier to change than the assembly.


If you have a factory moon roof, they would leak because the drain plugged up.


Then of course the resistor module would take a poop.


I can tell you how to remove the dash. I replaced hundreds of them. The same goes for the iterior.


Those are all the real common problems besides the crummy paint they put on and they all crazed (cracks in the laquer.

The one I sold in 2009 had 68k and it was a maroon biaritz with a perfect red and white interior, Seat belt cover would crack and some of the plastic inside would change color from age. Almost every one I have ever seen the driver's armrest on the inner trim panel on the door would crack from the location of the power window switch. At one time there was some sort of repair for the arm rest. It was an after market fix.

Doors are very heavy and sag. We would adjust using front end shims. Inside door handles are cast and notorious for breaking.

I also remember problems with the fiber optics for the fenders and the rear optics. As I said, they are a great car if you keep these things in mind. Look at what happened, you jarred my memory!


I will take the time now and just write the repair for the blower motor.

Go to a parts store and get what you need. Only get a two throw toggle (on-off) with the highest amperage rating you can get. Get a 10' role of red #10 wire. Get a pack of yellow but connectors and a scotch lock with a bladed connector for it. Preferably yellow. You may have to buy a small package. One roll of cheap black electrical tape. For some reason the cheap $.50 cent roll has better adhesive than the $7 tape. In line fuse holder and 30 amp fuse, cheap test light and crimper/stripper. Get a can of spray silicone.

This will not be the easiest to get to the wires coming and going to the ignition switch, but I will tell you. you don't even want to remove the lower  dash if you don't have to. There are hidden screws by the ashtray and the lower dash goes all the way to the passenger side.

You need a 7mm or 9/32 nut driver. There are 3 screws that hold the black plastic hush panel under the driver's side of the dash. Remove the screws. Then you need a deep well 10 mm socket and ratchet to remove the two bolts at the fire wall. Remove bolts and then hush panel.

It is not going to be easy, but I really don't want you drilling a hole through the fire wall and having to use a grommet.

Take the silicone and spray only the center of a grommet going through the fire
wall. This thing may fall out of the fire wall and you will need to position. Hold a rag under where you spray trying to prevent leakage on the outside of the grommet. Do the same thing to the same grommet. You will see a number of wires in this black rubber grommet.
Now, get a steel coat hanger and straiten. Take one end of the hanger and bed into a loop. Take your new wire and don't strip it, put it through the hanger loop, leaving about an inch out of the loop. Once this is done, crush the loop as best as you can. You need the very flat almost crushing the wire getting that looped end as possible. It would work better with another person too. Now, tape the looped end and to the wire as well. Without hurting any wiring, put the other end of the coat hanger through the middle of the grommet trying to find a place where you have some room between the wires to push the hanger through into the engine bay. Bend your hanger in the engine area so you can pull. Pull and once the hanger is pulling the wire through another person under the dash can pull back if the wire gets stuck in the grommet. Pull the hanger and wire through. Once wire is in engine area, cut wire end and throw out the hanger. The worst is done!!!

Run your wire across the fire wall to as far as the blower motor. Pull the one wire with the rubber tip off the motor. Cut the wire leaving enough to splice you new wire. Strip the end that you cut from the blower motor. Strip the end of your new wire. Use the yellow butt connector.

Put each stripped wire as deep in the butt connector and crimp. Lightly pull each end checking your connection. Tape each end with tape going from butt connector on each side just to secure connection. Reinstall blower motor connection firmly.

Now, just to make it easy to get quick access to the fuse, cut your new wire in the middle of the car and strip both ends and use the yellow butt connectors to attach fuse holder. Install your 30 amp fuse. Pull any excess into the car.You don't want this wire real tight, and attach your wire with small plastic tie wraps to the factory harness. You are done under the hood!

Take the test light and poke into the thicker 10 gauge wires with key on. Turn ignition off and there should be no power. This is known as switched power and that way if you forget to turn the fan off, no problem, it will shut off without you worrying about running battery down.

Once you find the wire, put your scotch lock on with pliers. You will feel it snap together.


cut a foot off your wiring. Strip both ends. Install you wire into your scotch lock bladed end. crimp and tape to secure wire. Install bladed connector into scotch lock firmly. Cut the other side of the wiring and leave it to the length of the lower dash.

Now if you want to do this right, drill a hole in the hush panel where the switch is easy to access and install switch into hush panel. Tighten the toggle switch. I do not know if the switch requires connectors or if ou can just install your stripped wires. Ask the parts guy when you get the toggle. Reinstall hush panel and check it out. You will have high blower and off with ignition on.

Good Luck!

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