Somewhere between replacing the Alternator and replacing the Heater Blower fan I lost power when the fan is turned to high. Checked the power to the fan with a test light and when on high I am not even getting power to it (thought maybe it was the new fan) but no. Checked resistors and all of the lower speeds work, just no high speed.

Has anyone else run into this problem?

 

Does the car have AC? If so, check the high speed relay & associated fuse. Not sure where they would be on a '68 but believe there will be a wire coming off the horn relay with an inline fuse holder. Check that fuse & follow the wire to the high speed relay. If no AC, not sure where to point you.

 

As stated previously, high blow relay if the vehicle has AC... If no AC, check the blower control switch on the heater control in the dash....

 

The car does have AC and the relay cycles when the fan is turned on and it clicks when the fan is turned to high but the fan shuts off.

 

Then check the connection at either end of the wire that goes from relay to the resistor board, or the wire itself. And as stated above, check the inline short fuse inside the little rubber boot near the horn relay.

 

When you say you have power at the fan, how are you testing this? If you are using a low-impedance voltmeter, it can show voltage even if current is insufficient to operate the motor. A test light or a high-impedance VOM are much more accurate test methods. If you have a corroded connection or other high-resistance connection anywhere from the high speed power source through the relay contacts to the motor, a low-impedance VOM will show 12V but the motor won't be able to draw enough current to turn.

 

^ an alternative test is with a lamp style voltage tester. I have a good meter but still use a lamp device when testing for true output. $15.00 auto store toy works great. They will glow dimly when current is low. Bright is Right. A must for trailer harness point to point testing.

 

Which is why I said this above...

 

Oops missed that. Got focused on VM function and fail.

 

Than you everyone. I was using a test light. It was a fuse in the line to the relay.

 

I believe I have the same problem and don't want to damage the rubber boot fuse holder. Can someone tell me if there is a trick to get it open to check the fuse? I have twisted and pulled hard on it and it wont budge.

 

I just bent the two halves and twisted. It came apart very hard and it broke the fuse which was blown anyway. Pulled the two halves of fuse out, used a tiny amount of dish soap and it slid right back together.

 

Ok thanks for the response, I will try and pull mine apart without damaging the holder.