Is my T/S & Emergency switch bad!

When I press the brake pedal, I only get power to one side of the rear lamps. I verified by taping the two wires that run in the sill plate on the drivers side to verify I had power to one side but not the other. The single culprit in the circuit is that switch. Do I give NPD an order?

I would also check the voltages at the connector on the steering column, make sure it's not a problem with the wiring ahead of the door sill. Because you'll have to pull the steering wheel to replace the switch I would probably pull it now, to verify that the switch is the problem. Chances are it is the switch.

Why won’t my 30 year old puller set that says, steering wheel, on the cover, fit this steering wheel? None of the threads work, and the holes are too close together, using the puller flange, to put any bolts in it anyway. Is there some special tool for this car? Do you think the Autozone for rent one would work?

Ok, I checked the power from the stop light switch is solid going into the switch, it I’m still only getting power to one leg. If it’s not the switch, I don’t know what it could be. I still can get the steering wheel off to pull in out and check it.

Steve McMahan said:

Ok, I checked the power from the stop light switch is solid going into the switch, it I’m still only getting power to one leg. If it’s not the switch, I don’t know what it could be. I still can get the steering wheel off to pull in out and check it.

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A few thoughts to ponder. Do both your left and right turn signals work? If the turn signal light does not work on the same side as the brake light that is not working you could have anything from a turn signal switch, to a wire that has broken, to a bad 1157 bulb, to a failed ground circuit at the taillight. That you have already decided to dive into the Turn Signal Switch tells me you are not a novice to electrical systems. But, I do not know if you have a schematic. The electrical schematics for 71, 72, and 73 Mustangs are similar, with a few changes here and there. But, I am pretty sure the 71 through 73 Mustangs share a lot in common with the turn signal and brake light circuits for the taillights. I have attached a PDF file snippet of the pages I think you will find useful, with color coding info as well.

Although you sounds like you have been around the block with electrical systems, I ask you indulge me for a bit. Some of this may seem mamsy-pamsy, easy, and obvious. But, too often (still) I find often needless deep diving occurs when the basics are overlooked. At the risk of embarrassing myself with some perhaps needlessly simplistic thoughts I offer the following...

Using a test light/probe (after ensuring its bulb is good) go into the trunk and with the 4 way emergency flasher working test the Circuit 5 (Orange with Light Blue Stripe wire) at the taillight pod sockets on the Right side. The test light ought to flash on and off. Do the same for Circuit 9 (Light Green with Orange Stripe). on the Left Side.

The reason I suggest using the 4 way flasher circuit to test the brake light circuits is because the 4 way flasher system sends current to both the left and right turn signal/brake bulbs at the same time, through the turn signal switch. If the circuit lights the test light, but the brake light/turn signal bulb(s) is not lighting, it is either a problem with the current getting to the bulb and filament (corrosion), failed bulb, or current leaving the bulb not getting to ground.

If there is no current getting back to both Circuits 5 & 9 in the trunk, you now at least know what color wires to test at the wiring harness that comes from the turn signal switch (the wire color for Circuit 5 or 9) not lighting up the test light in the trunk area. If you are lucky the side not flashing with 4 ways (on the same circuit wiring used for braking) is not lighting up the test light at the turn signal harness for either of the wires for Circuits 5 & 9 (the Orange Between with Light Blue Stripe and Light Green with Orange Stripe wires), depending on which side the failed brake light exists. If both wires are illuminating the test light at the harness near the turn signal switch you have a break in the connection between the turn signal switch and the rear 1157 bulb(s). If either of the two circuits fail to light the test light near the turn signal harness the problem is most likely the turn signal switch. I saw "most likely" because there is always the possibility the wire that is not lighting up the test light might have a failed connection at the turn signal switch itself (I have never seen that happen, but...).

I hope that helps, and that you find the schematic snippet useful.

I remember replacing the turn signal switch in my old 71 Sportsroof when I was a teenager because of the same brake light issues that were exposed to me at DMV when getting the car reinspected. Ahh… memories… good times

The DMV, that could be a fun thread.

Thank you for the very nice wiring diagram. Ok, here’s what I found:

When I engage the emergency flasher, I get all bulbs flashing. Turn that off, then I press the brake pedal, only the r/h rear bulbs. The turn signal is hard to move and doesn’t work on either side, even after replacing the flasher (JIC), and making sure I had power at the T/S flasher. So, I deduced from those tests, I have good wiring and sockets/bulbs (since I changed all 4 bulbs ), the brake switch is sending current to the T/S switch, and the overall condition of that system is good, but I have a bad/broken T/S switch.

I also have an old ignition switch that will not move to the accessory position, so I’ve got to replace that anyway, and I’ve ordered both for this week delivery. But, I still haven’t been able to get the steering wheel off, so I’ve got to figure that out.

Thank you the diagnostic plan you provided. I think too often we (me) are ready to replace parts before we‘ve determine it needs to be replaced. I appreciate the effort you went into to provide me this. Steve

Steve McMahan said:

The DMV, that could be a fun thread.

Thank you for the very nice wiring diagram. Ok, here’s what I found:

When I engage the emergency flasher, I get all bulbs flashing. Turn that off, then I press the brake pedal, only the r/h rear bulbs. The turn signal is hard to move and doesn’t work on either side, even after replacing the flasher (JIC), and making sure I had power at the T/S flasher. So, I deduced from those tests, I have good wiring and sockets/bulbs (since I changed all 4 bulbs ), the brake switch is sending current to the T/S switch, and the overall condition of that system is good, but I have a bad/broken T/S switch.

I also have an old ignition switch that will not move to the accessory position, so I’ve got to replace that anyway, and I’ve ordered both for this week delivery. But, I still haven’t been able to get the steering wheel off, so I’ve got to figure that out.

Thank you the diagnostic plan you provided. I think too often we (me) are ready to replace parts before we‘ve determine it needs to be replaced. I appreciate the effort you went into to provide me this. Steve

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You may have found this out already, but just in case. The T/S Switch for fixed steering columns is NOT the same as for tile wheels. Choose carefully... I found this out by observing someone else trying to fit the non0tilt- version of the switch into a tilt wheel column. I do not recall the differences, but the fixed wheel switch simple could not be made to work, much to chagrin of the tech who tried to force it to work,

I ordered the non-tilt. That and my new ignition switch.