AC Blower Blows fuse on high speed only

[Norm Waters]

Blower works perfectly on low, medium and medium high but when switched to High it blows the fuse immediately. I suspected the switch or blower resistor so I pulled the 3 wire plug at the resistor to take it out of the equation. When turned on high it still blew the fuse. So I pulled the dash pad off to get to the plug at the back of the switch, I found a yellow wire tapped to the back of the plug in the same location of the brown wire for high speed Any ideas what is up with that? Could this be the  cause of the fuse to blow when switched to high speed? The wiring diagram shows only the brown wire in the high speed switch location.

[Kurt]

The brown and yellow wires are actually tied together in the wiring diagram but in the diagram it appears to be at the firewall bulkhead connector.(see red arrow in pic) Not sure why they don't show it tied at the fan speed switch location. Electrically it doesn't make any difference whether it is tied at the switch or bulkhead. I assume your wires look original and not re-spliced, correct?  My guess is that the fan speed switch might have a short when switched to "high". You can test the fan high speed operation by connecting 12V directly to the fan. Since it works on all other speeds, it's probably OK. 

Next reconnect the brown wire to the fan and try 12V directly to the brown/yellow wire (connector disconnected from fan speed switch). If that works, problem is most likely a short in the fan speed switch.

[Norm Waters]

Kurt thanks for the reply. That makes sense it shouldn’t affect electrically. If it is determined the switch is defective at the high speed setting could I just remove the dark green medium high wire before it goes through the fan speed resistor and tap into the yellow wire? If I’m thinking correctly this should make the medium high position high speed? This would only be temporary until I can locate a switch and wait for cooler weather to install since I here it’s a difficult process.

Thanks!

[Kurt]

Correct. If you tie the dark green wire to the yellow wire, 12V will travel directly to the motor and skip travelling through the resistor even if you don't detach the wire at the resistor (since current likes the path of least resistance).

You can confirm a defective switch by doing a continuity test to ground on each terminal of the switch (plug disconnected) while moving the switch through each position. None should be grounded.