My fuse keeps blowing when heater fan is turned on. I looked for a short from blower fan to fuse block, but could not find problem. I disconnected orange wire to blower fan (which is new) turn the switch on and still blew fuse. Could resistors have gone bad, or a switch gone bad?

Is this an A/C equipped car?

It is a NO/AC car

You could see what happens when you pull the connector to the resistors, then turn on the fan.

Does it matter what speed the switch is in when the fuse blows? Try putting the fan switch on one speed at a time, then install a 10 amp circuit breaker. Saves on fuses during trouble shooting. See which speed the circuit breaker trips on. That will give you an idea which wire to trace for a short to ground.

Larry

I put the blower fan switch on "high", and then installed new fuse. Needless to say, it blew the fuse. It blows fuses at all blower fan speeds. I'll dig further into it this week.

Try my diagram. It's for a 69 Camaro, but should be close. Like most electrical problems, it's sounds like a very simple problem; it might take take a couple hours to find the problem but only a five minutes to fix. Before you start tracing wires, disconnect the resistor connector and the fan switch connector and see what the results are. You never know. Always do the simplest things first. But, it seems like the the orange wire is shorted to ground.


Larry

http://www.myimagehosting.com/pic.php?u=1808aaKnA&i=16284

I disconnected resistor plug and fuse blew when trying to turn fan on. I looked for bad wires between fan switch and resistor, everything looked fine. For some reason I'm leaning toward a bad fan switch. The orange wire from blower motor to fuse box looks good. God I love electricity!!

Save some money on fuses until you get it fixed. Remove the blown fuse. Clip a test light across the fuse clips. If there is a large short..like you have..the light will light up. When the test light is on, try removing the connector off the switch as your next move.

I put a test light across the heater fan fuse terminals. The light did not come on until I turn the fan switch on. I removed the ash tray and radio and unplugged the wires going to the fan switch. The light remained off. I inspected the plug and wires, everything looked good. Does this mean the switch it's self is bad?

Great testing. The light test showed something.
1, The wire to the fan switch (I believe brown) is not shorted.

Since we are using a light to check things, there is no power on the wires. This lets us try a couple of things that we normally couldn't.

Make a probe to stick into the fan switch connector contacts. A probe can be made up of a flattened piece of wire. Even a paperclip will work. Flatten it with a hammer so it goes inside the connector contact.
Use a jumper lead to jumper the probe from the brown connector contact to the switch contact. In this way you are only attaching only the brown wire to the switch.
Now try the light test again. Move the switch through all the different positions. See if the light comes on.
If it does the switch is bad.
If the light does not come on, remove the jumper from the switch. With your flattened probe jumper brown to one of the other contacts in the switch connector. See if that makes the light come on. If it does post back with the color of the second wire. If it doesn't, move the probe and jumper brown to another terminal.

The idea is to see if one of the other wires is shorted by making the light come on. I'm guessing it's not the switch but one of the other wires on the switch. Just trying to see which one.

OK, I jumped the brown wire(connector) to the switch terminal for the brown wire, moved switch to all positions the light did not come on. So that means switch is good. I left jumper in brown wire (connector)and removed the other end from switch, then jumped to the 2 orange, lt blue, and yellow in the same connector. The light stayed on for all three. I'm hoping I did this correctly. If so, whats next? Thanks.

Well, the test with just the brown wire to the switch showed that the switch is not shorted to ground. It shows that the switch is not causing the fuse to blow. Doesn't 100% mean the switch is good, only that changing it right now won't fix the blowing fuse problem.
Since the light came on when you jumped brown in the connector to each of the other colors, suspect that you have the other connectors plugged in.

Unplug the connector from the speed resistors under the dash.
Unplug the yellow wire from the motor.
Repeat the test jumping brown in the removed switch connector to the other colors. If the light still comes on post back the results.
If the light does not come on, install the speed resistor connector and repeat the brown wire jumper test.
If the light now comes on, post back the results.

I unplugged the orange wire leading to the blower motor and unplugged resistor plug.

Jumped Brown wire on fan switch connect to LT/Blue terminal in same connector-- No light

Jumped to yellow wire in switch connector-- No light

Jumped to double orange wire Light came- ON

With resistor plugged in

Jumped brown wire on fan switch connector to LT/Blue terminal in same connector Light -ON

Jumped to yellow wire Light- ON

Jumped to double orange wire Light- ON

Resistor Bad???

No, the problem is the orange wire is shorted to ground. To prove this again:
Leave the orange wire off the blower motor.
Leave the connector off the resistors.
Plug in the speed switch connector.
If I see it right, the light will only come on in the blower switch HI position but will be off if the switch is in any other position.

John, you are correct! With orange blower motor wire unplugged, and resistor plug unplugged, and fan switch plugged in. The light ONLY comes on when fan switch is turned to the High position. What's my next move?

You are down to the easy part... just one wire is causing your problem.

Unfortunately that one wire run quite a long ways: from the switch to the harness back to the fuse panel where it connects into the firewall bulkhead. From the bulkhead connector it runs all the way across the firewall to the blower motor. A lot of wire and a lot of possibilities for a short.

You could try removing the wire from the bulkhead connector to isolate it to inside or outside the firewall.

Or... you could take a gamble and play the probabilities. This particular wire runs all by itself from the end of the wire trough down around the blower duct, across the bottom of the duct, and up into the blower motor. I would personally closely examine that portion of the wire for ground contact and worn insulation. Note that moving the wire may make the contact go away only to return another day if the problem has not been fixed.

Vroom's correct. It may take a little time to find. The posted schematic is not quite correct. You've noticed that there were 2 orange wires in the switch connector. Either one of those could be the culprit. One orange wire runs over to the resistor connector. The other orange wire runs to the bulkhead connector behind the fuseblock.
You could start by examining the orange wire to the resistors. As Vroom says it's pinched somewhere inside or under the hood. Maybe leave the switch in HI and wiggle the wire to see if the light goes off in HI.
Suspect it's more likely a problem in the other orange wire. The one that runs from the switch connector to the bulkhead connector. From the bulkhead connectors it runs over to the blower motor.
Might try disconnecting a battery cable (for safety). Then unplug the engine harness connector under the hood. The engine harness connector is the inside connector of the 2 connectors in the firewall. It's the one that contains the orange wire. After you remove the engine harness connector, reconnect the battery cable and see if the test light is OFF in the switch HI position.
At least that will tell you if the orange wire has a problem under the hood or inside the car.

Well, I found the short!! After laying in an un-natural position for hours I found that the short was not under the dash! I thought with a new wiring harness in the engine compartment it could'nt be there! But it was! To make a long story short, I had a local shop (friend) of mine replace pump and torque converter seals in trans about a month ago. When he re-installed the trans he just nicked the wiring harness and pinched the orange wire between block and bell. Oh well. I would like to thank you guys for all the help and advise given! I learned alot about trouble shooting electrics. Hopefully there's another couple weeks of driving time left up here before snow flys. I want to reach that 500 mile break-in so I can really see what the old girl can do.
Thanks again!!
Jack

Cool, glad you found it. And pretty darn close to where I suggested you look too ;-)
Although I never would have guessed it would be bolted into the motor.

Steve

What is this snow stuff you speak of? Is it the same as the frozen stuff that's put into cones with syrup on top?

No syrup and we shovel it to piles!

OH MAN - This is my exact situation .. I'm following this ..

Is the 69 heater fan switch close enough in function to the 66 fan switch that I could use this same information to diagnose it?