Hello All,

Can anybody tell me which wires / plugs connect to the blower switch and the rear defroster switch? The defroster is the grid type, not the blower type. I started out looking to see why the cigarette lighter wasn't working and one thing lead to another and to another etc... I found several unhooked wires and disconnected plugs. The manual I have is terrible and the wiring diagram isn't even close to the actual wiring.

1972 Cutlass Supreme, 350ci with a/c

Thanks!

 

I would suggest a chassis service manual. But here is a thread and about halfway down Allan R posted a huge image of the wiring diagram.

https://classicoldsmobile.com/forums...-71-442-a.html

 

I looked at that diagram before posting. It doesn't seem to show the switches in the dash and I can't find the rear defroster mentioned anywhere. Here's what I found...the green wire is on the defrost switch and I think it should be on the top terminal of the blower switch...not sure though. Thanks for the link.

Oh, and it's hard to see but the white wire from the connector seems to be hard wired to the defroster switch...I think it goes to the red power on indicator light.

 

Looking at the picture again now, I'm wondering if the plug with the white and brown wires should connect to the defroster switch. There isn't any power going to either wire but that could be another problem. I don't know why there would be a 4 pin connector using only 2 spaces though...seems strange. Hopefully somebody has this same set up and I can see for sure. It makes sense though because if the brown wire supplies power then the white wire could go to the defroster and to the indicator light. I'll have to find out where the other end of the brown wire goes.

By the way, if power is placed on the bottom terminal of the defrost switch as pictured above, the blower motor comes on when I flip the defroster switch! That's why I think the green wire should actually be on the blower switch.

 

Well I got the defogger working now. I had to rebuild the switch that was blowing a fuse under the hood. It's a short fuse in a weatherproof housing and is attached to the top of the voltage regulator. I guess that prevents any battery issues when using the defogger as it won't turn on unless the engine is running.

Now I just need to figure out where that light green wire goes? It doesn't make any difference if I connect to the top terminal on the blower switch or not. It also has +12v to it, with key on only, I think.

Also, maybe related...I noticed that the low and medium low fan speeds are the same. Medium high doesn't work at all and high works fine. Blower motor resistor maybe?

Here's a pic of the fuse holder for the rear defogger:

 

I have a working Griddefogger on my 71 CS.
There is an extra relayadded to the fan blower circuit.
The fan wiring for a car with the Grid optionis different than a stock 71 CS with Air cond.

I did see a crude diagram in the CSM somewheretalking about the Grid defogger.

The extra relays for theGrid have two safety features.

When the car is off, theMain power to the grid defogger comes from the Horn relays to a Grid relay, viaa thick black wire with an Inline fuse (short fuse that breaks easily and ishard to find).

This cable looks identicalto the High speed fan power cable.

The grid relay will only getpowered on, when the external voltage regulator is seeing power from thealternator. This may be different withan internal regulator.

Another safety is that whenthe 4 speed blower is on high, and the Grid defogger is ON, the power to theHigh speed Blower is disabled. Thesystem will default to Speed #3. This isnormal.

The reason is the 63 ampalternator can’t handle the load at a stop light, Headlights on, Fan on High, withthe grid defogger ON.

In short, the power wire forthe High Speed Fan relay has to go to the Grid relay, so that when the GridRelay is ON, the power to the High Speed fan relay is removed.

 

That makes sense with what I was able to figure out. I can hear a relay turn on with the rear defogger but I haven't seen it. Thanks for all the info!

Any idea what the light green wire is for? And where it might go? The 1st and 2nd speeds are the same on the blower, the third isn't working at all, and the 4th seems to work fine. I can't remember for sure if that was with or without the defogger on. I never thought they'd be related at the time.

 

Just had a thought....could the light green wire be from a missing terminal on the defogger switch? it looks like there's a third rivet (under the yellow wire) but no terminal. Any idea if the defogger switch should have 2 or 3 terminals?

 

Duplicate, sorry.

 

Hi 79MKII

I have not touched my Dash Fan area yet, not sure where stuff goes at that end.
I would suggest you get all 4 speeds working first, and then try to fix the Grid Defogger.
It is all working this week. I did have some issues with blown fuses for the fan system (one fuse in the fuse panel and the other, In-line from the horn relay) and a burnt out fan from old age.

I used the attached diagram to debug the 4 speeds on the fan.
This print is for AC with 4 speeds. It does not show the Grid Defogger relay.
From Memory, the Grid defogger relay is used the Break the wire #8 Black/Orange.

The Black/Orange wire gets turned into a White wire coming out of the Grid Relay, which then goes into the

Blower Relay, when theBlack/Orange wires use to go.

Speeds 1, 2, 3 will work allof the time with or without the Grid Defogger.
Wire #8 for Speed 4, gets disconnected when the Grid is ON.

If you are missing speed #3, then unplug the cable from the Resistor pack and meter the voltage.
As you move the switch, you will see 12 volts on 1 wire at a time: Wires,5, 6, 7.
Remove and clean the resistor pack.

When you plug it back in, make sure all of the tabs on the resistor pack Mate with the black connector. I did loose speed #3; it was only that the TAB missed the plug when I put the connector back on.

 

I just looked at your picture with the vacuum can. Looks like CS 72 is similar. Your Grid safety does come off the External voltage regulator just like mine. That wire is for low current, just to turn provide power for the Grid Relay. The fuse should be low amps.

The main power feed for the Grid should be a thicker wire, which also has a inline fuse set for 30 amps.

I can see the White wire tothe left of the vacuum can. This wire will kill the (#8 black/orange wire) Speed #4 for the High Speed fan relay.

 

Great information. I'll dig into it a bit more this weekend. The defogger is working now, but the blower motor is not quite correct.

The fuse for the defogger coming off the voltage regulator is only 5 amps, low just like you said. Going by that diagram, it looks like the light green wire does in fact go on the blower switch. Just have to figure out why speed 3 isn't working....I'll check those things that you mentioned. Thanks again!

 

Just looked a little more closely at the wiring diagram. The 3rd speed, the one that isn't working on my car, is fed by the light green wire I was asking about. Coincidence....I don't think so! I'm sure it's something with how I have the wires connected at the blower switch, or possibly the switch itself.

 

After you get the fanworking correctly you can tackle the heating elements in the Grid.

A few of the resistor wiresin the grid may have cracked. I was ableto fix one of my broken elements with a kit from the local auto zone. It actually worked.
As for the wires, you willneed a good Volt Meter. Connect the Negativewire to ground. With the engine runningoutside and the Grid turned on, test each wire. Get some Post it paper with the sticky edge. Cut the paper into half inch sticky squaresand mark the squares 1, 2, 3 etc. Youwill use these as markers to identify bad wires later.

Do not use REAL tape on thewires. Tape will damage the wires.
Start testing from big stripon the far Right; you should see a full 12 volts.

Now go to the top centerwire and touch it.
Very very lightly tap theedge of the resistor wire with the positive volt probe.

You should see Approximately6 volts at the Center of the window wire.
If you see Zero volts, thebreak is to your Right (Driver Side).
If you see 12 Volts, thebreak is to your left (Passenger Side).

Mark the bad ones with thePost-it sticky paper.
Keep testing until you havechecked all wires (maybe 11 wires?).
After you have found all ofthe good wires and bad wires, now go back to the bad wires and test every inch or so, until you find the badspot. The bad spot may beInvisible. No visible scratches.

With the volt meter the badspot is easy to locate. The Right sideof a break will have 12 volts, the left side will have Zero volts.

Note: With a Good Wire, The closer you get to the Passengerside; the voltage will gradually drop from 12 to zero, gradually, this isNormal.

With a Bad wire, the voltagewill stay at 12 volts from Right to Left, until you pass the Break. At that point the voltage will drop to Zero. There is NO gradual voltage change for a brokengrid element.

 

Grid Defogger Test and Repair.
How the Grid works.
The grid is made up of 15 Resistor wires. Each wire is attached to a Ground Strip on the PS side,
and to a Positive strip on the Driver Side.
Each wire is actually a Resistor, connected in Parallel. You can only test Parallel Resistors with a voltage applied to the resistors.
The resistor wires on the CS do not have an Insulation coating, so you can easily take a voltage reading from each wire.
They are also very fragile. You can easy break a wire if you touch too hard with your voltage probe.
The DS side of the Positive Strip will show you the Highest Voltage of 12+ volts.
The Passenger side (PS) will show you the lowest voltage / ground.
As you move your probe from DS to PS, the voltage will gradually drop from 12 volts, to 6 volts to 0 volts (gradually).
All 15 wires should have a similar voltage drop.
The Engine must be running, Grid defogger ON, and the car parked in a well ventilated area.
Bad Wire Example:
In picture 966, you can see the meter reads 12.76 volts. This reading is collected from the 7th grid wire.
The probe is approximately 10 inches from the Passenger side ground strip. At this point I should be seeing approximately 2 volts.
Since I am reading 12.76, it means that this grid wire is broken. The break is somewhere towards the passenger side of the wire.
Good Wire Example:
Picture 967 shows an example of a good Grid Wire. The voltage is 1.32 volts.
Since this wire is only 4 inches from the Passenger Side Grounding strip, this is a good reading.
Patch:
Picture 970 shows part of the repair process. I used a kit from Permatex Complete Rear Window Defogger Repair Kit.
This kit did work. You need 1 kit per broken line. The white paper is a stencil that is placed over the broken resistor wire.
Next you paint on several coatings of metal paint. I put on 10 coats over a 1 hour time period.
After you remove the stencil, the stencil will usually break and cannot be reused. I waited 2-3 days before testing the repair.
It actually worked.





Above, broken wire example







Above, Good Wire example





Stencil in place during repair.

 

Wow, I never knew you could measure voltage directly from the grid. I will definitely try this when I have a chance. Awesome information. Thanks

 

Grid Defogger Update:
It has been 4 years since I installed the Permatex patch kit to fix the Rear Window Grid.
Since I rarely drive in damp weather I do not use my Grid that often. On those rare occasion I did get caught in the rain, the patch I made to the Grid is still holding after 4 years.

Grid Defogger Side effect:
The Grid Alternator Relay does draw a small amount of power from the Generator Light Circuit. This is by design to prevent the Grid from running when the Engine is Stopped. As a result, when the Grid is ON, the Generator light will glow slightly. It does not mean there is anything wrong.

I also replaced my 63-Amp 10DN alternator with a clone 10DN that makes 100 amps on the highway and over 60 Amps are crankshaft RPM of 700.