[Cracker289]

I don't see in the diagram, or labeled on the fuse box, which circuit feeds the horn. I'm a little old and chunky to climb under that dash very many times with my multimeter; anything that can help me isolate and fix problem as quickly as possible is highly appreciated!

 

[Veronica]

Hello. The horn wiring doesn't go through the fuse box. There is a yellow wire that comes from the headlight switch and goes up to the horn button, then the blue/yellow wire goes out to the horns. Here is what the fuse box does.
The Care and Feeding of Ponies: Mustang Fuse Box 1965 1966

 

[Cracker289]

Hello. The horn wiring doesn't go through the fuse box. There is a yellow wire that comes from the headlight switch and goes up to the horn button, then the blue/yellow wire goes out to the horns. Here is what the fuse box does.
The Care and Feeding of Ponies: Mustang Fuse Box 1965 1966

Hi Veronica, I realized today that I caused the horn to not work due to some wiring mistakes I made under the hood. I installed a relay for the horn and I had it hooked up wrong!

 

[Veronica]

Hi Veronica, I realized today that I caused the horn to not work due to some wiring mistakes I made under the hood. I installed a relay for the horn and I had it hooked up wrong!

Hi again. I hate it when I do that. :gringreen

 

[Cracker289]

Hi again. I hate it when I do that. :gringreen

Hey Veronica

Can you lend your expertise for a moment. This yellow wire has no power to it when key is on. In this diagram it is number 913. Goes to the heater blower motor.

http://hammar.dyndns.org/~djhamma/wiring/1966/66acces1.jpg

However the heater fuse is good, has 12 volts on both ends, and according to the diagram the yellow wire is not going to the fuse box anyway. I can't figure out why this stopped working. Does the yellow 913 wire only have power if the fan is good? Or am I missing something obvious. I've checked fuses and connectors. My back is killing me from being twisted up under the dash and my face is beat to heck from everything I've banged it against while trying to get out from under the dash. I'm getting frustrated cause I can't figure it out myself!

 

[Veronica]

Hi again. How that is supposed to work on your car is that there is a brown wire coming out of the fuse box that takes keyed power straight to the blower motor. The yellow wire coming out of the blower motor goes to the resistor, and that three wire connector going from the resistor to the switch is what takes power to the switch, with the switch housing working as the path to ground, with the position of the switch determining which of those three wires is actually grounding out on the dash. So, with the key on, that yellow wire plugged into the front of the resistor should be hot. If it is not, I would unplug the yellow wire from the heater blower and see if the yellow wire coming out of the motor was hot. If yes, the problem is with that yellow wire somewhere along its path to the resistor. If no, unplug the brown wire and see if the wire that you unplugged from the blower, not the wire that is coming out of the blower, is hot.If yes, the blower motor is bad. If no, the problem is somewhere along the browm wire between the fuse box and the blower.

As a side note, you're supposed to crawl through the glove box, slither underneath the radio and then wrap yourself around the steering column like a tree boa to avoid beating yourself up in there. I think that this is even in the shop manual supplement.

 

[Cracker289]

Hi again. How that is supposed to work on your car is that there is a brown wire coming out of the fuse box that takes keyed power straight to the blower motor. The yellow wire coming out of the blower motor goes to the resistor, and that three wire connector going from the resistor to the switch is what takes power to the switch, with the switch housing working as the path to ground, with the position of the switch determining which of those three wires is actually grounding out on the dash. So, with the key on, that yellow wire plugged into the front of the resistor should be hot. If it is not, I would unplug the yellow wire from the heater blower and see if the yellow wire coming out of the motor was hot. If yes, the problem is with that yellow wire somewhere along its path to the resistor. If no, unplug the brown wire and see if the wire that you unplugged from the blower, not the wire that is coming out of the blower, is hot.If yes, the blower motor is bad. If no, the problem is somewhere along the browm wire between the fuse box and the blower.

As a side note, you're supposed to crawl through the glove box, slither underneath the radio and then wrap yourself around the steering column like a tree boa to avoid beating yourself up in there. I think that this is even in the shop manual supplement.

What if I told you the brown wire under the dash is fluctuating from like 3-5 volts? This might be where it is coming out of the fuse box, there is a 2 lead connector (yellow & brown) near the fuse panel, I disconnected it and the brown wire is fluctuating like I described (when i turn the key on, 0 volts when I turn it off).

You know what I need is lonnnnng skinny arms. :shiny:

 

[Cracker289]

Ok Veronica, you nailed it! I pulled off the wire loom so I could check for voltage, and guess what - both wires disconnected. Also noticed in the same general area, the transmission dipstick handle is bent down. Looks like the guy that did my hood and fender alignment probably disconnected by mistaken while working back there and with the wire loom still covering it, did not realize.

 

[Swan1966]

When did the 66's go to a 20amp fuse for the Lighter/Emer. Flasher in the fuse block?

I checked out Veronica's picture, from a 1966 wiring harness, it has the 14 amp block for that fuse. I am replacing mine, pulled it out and saw that I have a 20A fuse for those items. Mine is a standard, stock 1966 wiring harness.

I am putting in the repro wiring harness, the new fuse block also denotes this socket as 20A.

Not that it makes any difference now, but did the 66's have two different wiring harness that changed fuse blocks sometime during the year, or were they perhaps at times, plant dependant, working with left over stock from 1965?

My car was built 4/2/66-Metuchen

My 1966 Mustang was a Metchen NJ car as well. How can I find out what day it was built? My VIN is 6T09A252199.

 

[GT'sGT]

Here's what I did with mine:

It uses the newer blade fuses and has 5 empty spots for adding additional components to the car. When a fuse blows, the LED in the window lights up so you can see instantly what fuse is bad.

I recommend at least putting in the new fuse holder kit that is sold for these cars.