OK, on a serious note, without any "Chardonnay..." (just for today
Since we have moved this over to "General Discussions ~ Processes & Techniques" the information already shared to this point MAY not match up to every example out there (example, pin connections in the TS harness to main under dash harness, the O.P.'s Mercury looks to have a curved plastic bulk connector at this juncture point where I know other examples do not). Another situation is that the '66 and older Mustangs DO NOT incorporate the hazard flashers into the steering column, though the basic function of the Turn Signals is 100% the same. (67-up has more wiring to work with in the column) I'm not trying to nit-pick details since I am sure the information is most likely 100% correct for the O.P's example.
What I am asking is, that for clarity purposes, that perhaps not only the wire 'color' be described but to possibly consider including the circuit number that Ford engineers provided in the descriptions/comments. Ford used the same circuit numbers for many years just like they usually used the same wire colors for many years. This added "circuit number" (with the wire color) could aide in translations to other applications for future readers of this thread. I know when I trace out schematics I like to use both so those readers who are "wired" like I am, this could help us a LOT!
Just a suggestion, not trying to derail or hi-jack the thread in any way. To explain what I am suggesting, using Midlife's previous quote (with only detailed wiring colors), I have copied his text and added (high-lighted in red) the particular circuit numbers. I have confirmed the circuit numbers using the 1967 Osborne Assembly Electrical Manual, page 96, that these wiring colors shared earlier MATCH 100% to my wiring diagram of my 67.
OK...you're getting power to the turn signal switch. Let's turn to the turn signal switch itself. First, disconnect it from the underdash harness and you'll need to set your DVM to resistance, ohms, or the upside down U. No need for the key to power anything. Put the turn signal switch lever in the neutral position and look for resistance between the blue wire (circuit # 44) and the following: white/blue(circuit # 49), green/white,(circuit # 50) orange/blue(circuit # 5), and green/orange(circuit # 9). These wires are in the center of the turn signal switch connector, top and bottom row. You should see high resistance between blue and these wires.
Now put your turn signal switch to the down or left side position. Measure resistance again as above, and you should get low resistance for the green/white (front) (circuit # 50)and green/red (rear)(circuit # 10) lamp turn signals. High resistance for the other two wires.
Put the turn signal switch to the up or right side position. Resistance should be low between blue(circuit # 44) and white/blue (front)(circuit # 49) and orange/blue (rear) (circuit # 5)wires. High resistance for the other two.
Now then...brake lights come from the green wire(circuit # 511) below the blue wire(circuit # 44). You can measure resistance between the green wire(circuit # 511) and the four above. You should see high resistance for the white/blue(circuit # 49) and green/white wires (circuit # 50)and low resistance for the green/red (circuit # 10)and orange/blue wires(circuit # 5), with the turn signal lever position in the neutral position.
Post the results and I'll bet 67gtasanjose's afternoon chardonnay glass that the turn signal switch is bad.
I think I copied over the correct circuit numbers, anyone is welcome to double check.
My money, (no booze, or Chardonnay
) is on connection issues and/or incorrectly pinned connector(s) (pins plugged into incorrect cavity perhaps) We'll see. Randy does these things far more often than I do and either is suspect at this point of time for the O.P.'s situation IMHO