REPAIR MANUAL MISTAKES ? 1978 Cadillac Load Level relay

Started by R Schroeder, January 16, 2011, 10:12:19 AM

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R Schroeder

This is out of my repair manual for checking the relay for the load leveler system. Pretty simple check, but I believe it is wrong.
This is on page 3D-6  1978 repair manual.
Step 4 tells you to ground BLUE wire. Well this is the hot wire coming into the relay. To me grounding it will only blow the fuse.
GREEN wire is hot AFTER relay is pulled in . Yellow is ground for the relay coil.
To me this test is wrong.

Step 5 tells you to , unplug wiring harness from relay , put a jumper on GREEN wire and YELLOW wire. Well, yellow is ground, and green isnt hot until the relay is pulled in, so this will do nothing , since its unplugged to begin with , and there is no hot wire involved .
So, I feel this is wrong too.
Any thoughts.

I'll ad the relay view too.

Joe 12138

Roy: on the polarity markings on the plugs in your pictures from the book, or did you draw them in? If so, are you sure? Sometimes one has to use "backwards thinking" with GM wiring schemes. Many circuits are completed by switching the ground rather than the "hot" (positive) wire.
   Without having the whole electrical drawing in front of me, I can't tell true polarity for sure. But Cadillac usually uses a black for the direct connection to ground (negative). This leads me to believe that possibly the dark blue is "on the way to ground" but switched by something else, possibly the ignition switch or another relay.
   If your polarity marks are wrong, in relation to frame of car, I believe the switching is being done to complete the circuit via ground paths. If so:
   Test step 4 does 2 things. (A) Verifys power (Positive in relation to car frame) availible at pin 2 (yellow wire).  (B) This also tests continuity of coil in relay.
    Test step 5 also does 2 things.  (A) Tests for power (+) at pin2 (Yellow) and (B) tests for continuity across relay contacts when relay is pulled in.  If the polarity is that the yellow is the supply to the relay coil and contact, these tests should be harmless. A fuse could still blow if there's other issues, but the test itself is probably valid. 
Good luck!...Joe Gibeault

R Schroeder

I'll send you a drawing after the football game......ha
But, the system is like this.
BLUE comes from fuse box. So it is hot. 12 volts. Key switch turns on the power.
GREEN goes directly to the compressor on the car. It is then completed by the grounding of the motor to the car frame.
YELLOW is the ground which goes to the rear control on the load leveler, and is then grounded through a black wire, when switch is made.
In third picture you will see the coil inside of the relay is picking up power off the BLUE wire. It then grounds through YELLOW to BLACK in the rear switch, to complete the circuit.
I did put the plus and minus marks on the drawing for clarity.

R Schroeder

Joe 12138

Roy: So., maybe the impedance of the coil will keep the fuse from blowing if what you say is true. I'd press the "I Believe" button, trust the shop manual and risk a fuse to find out. Damn the torpedos, full speed ahead!
No guts, no glory!
Joe Gibeault

R Schroeder

Sorry Joe, but when you ground a hot wire it will blow the fuse. The relay coil is a dead end without the yellow being grounded, so that is no help.

Step 5 is still checking a dead wire to a ground wire, so that isn't right either. No power going through those.
I don't have a problem with my car. I have a problem with the manual..................ha

I have caught printing errors like this in John Deere manuals too, for my tractors.

J. Gomez


If the third picture on your post is from the manual the +12V source would be switched by the relay contacts on this case via the terminal connection to the blue wire. Traditionally the switched side is the positive side and the yellow would then be the ground source, unless of course they switched the polarity for this application.  ???

From your diagram I can’t see what will switched off power to the relay and to whatever it powers since the blue is always hot? The yellow would be the once switching power to the relay??

Steps 4 tend to indicate the blue is ground while the yellow is the hot side, and step 5 is valid under this assumption.

If your hand trace wiring diagram matches the manufacture wiring diagram as you mention the manual is incorrect with these testing steps. But again the last pictures contradicts them when the blue is the +12V feed.

Good luck..!
J. Gomez
CLC #23082

R Schroeder

The drawing is correct. It is the part of the system that turns on the compressor.

Again, the BLUE wire is the hot wire . It comes from the fuse box. It is hot when the key is on. It supplies power to the compressor through the relay. Comes in on BLUE and goes out on GREEN.
The Yellow wire is the ground wire for the coil inside the relay. It runs to the level control box at the rear of the car.
The yellow runs to black ground  when the switch closes, there by turning on the compressor , by grounding the relay coil.

If you follow the system , you will see that the book is wrong on those two steps.

I sent you the diagrams , Jose.

Again in step four ,they are showing a jumper wire that is going to ground. If this were done it would short out, because the BLUE wire is coming from the fuse box, which is a power wire.
It isnt showing that the BLUE wire is a ground wire.

R Schroeder

Here is a simple drawing of the system.

J. Gomez


I would say the picture of the relay socket on step 4 and step 5 are reversed on the manual. If the pictures are reversed it would make them in synch with the steps.

Good luck..!
J. Gomez
CLC #23082


I am not familiar with this car or the electronic level control, but normally GM color code is red, yellow and orange wires are power.  Red is the most direct to the battery while yellow and orange are switched some how. 

Glen Houlton CLC #727 
CLCMRC benefactor #104

R Schroeder

Jose - that would not help, because the caption on the top , of each step , would not match the drawing.

Glen - to a certain degree you are right.
But if you looked at a dimmer switch for this car the yellow would be a hot wire feeding the switch, and in the case up above the yellow is a ground wire closing the circuit for the relay coil.
So, they are both switched , but one is hot in one case, and a ground in the other.

In the load leveler wiring harness running to the rear of the car there is also a white ground wire for the solenoid ,which opens the air valve to lower the car . It is fed by the same BLUE wire that feeds the relay. BLUE in, and WHITE out to ground. When white is grounded , solenoid works.
Both the yellow and the white wire go to ground through a black wire , at the rear switch.

Both of the steps in 4 and 5 are wrong.
Forget about the color of the wire and just look at it as hot and ground.

R Schroeder

Glen - to make this drawing even more simple, change the blue and green wires to red. Change the yellow wire to black. This would then be a basic wiring system . RED - hot . BLACK  - ground.

J. Gomez


Please ignore my last post to fast on the trigger before looking at the wiring arrangements.  :-[

Looking at them closer you are 100% correct both of these steps are incorrect in the manual as shown. Step 4 should be ground to yellow and step 5 should be strapped blue and green.

Good catch..!
J. Gomez
CLC #23082

R Schroeder

There ya go. Thats what I was trying to relate.

In my spare time I read the manual for the car. Something did not seem right. I have caught mistakes in my John Deere manuals too.

Step 4 should read , ground the yellow wire to check the relay coil pull in . If it pulls in and compressor runs, then you know you have a problem with the wire going to the rear of the car , to the control box. It could be a bad switch back there or a broken wire to it.

If it still didnt run then you would go to step 5 to check the contacts in the relay, by jumping the green and blue. If it came on , you would know the contacts are shot in the relay.

David King (kz78hy)

Anyone got the next years Cadillac Serviceman Bulletin?  That is where they would note and correct errors.

David King
CLC 22014  (life)
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R Schroeder

Mike Jones sent me a diagram of the level control system. This is the box mounted at the rear axle.  It shows  YELLOW going to ground, and WHITE going to ground for the air release solenoid.
This proves the book is wrong.

JOE - I cant push the " I believe button " until I know its right.
I have seen a couple of friends , back in high school , turn there wiring harness a beautiful red glow and watch the plastic drip to the floor. They then stepped back and said " Oh @#$%........................ha

R Schroeder

I spent a couple of mornings now trying to search TSB's on Google.
Even went to the government site , NHTSA. Boy have  they ever gone south. Typical government site though.
They take you to sites where you pay for the info now.
They also dont even list a 1978 Cadillac on there site. They do for Buick and Chevy though, and some cars that have not been made in a hundred years. Government idiots.
So, I'm lost as to where you get them.