Check the resistance across the brake light switch. Maybe you're getting too much loss across it and it will only let one lamp light, or fully light. Also check the voltage at each lamp under load. I notice you have black out lenses, so one lamp may be lit dimmer than the other and you can't see it.
1983 Mustang driver side brake light issue
Mother of God, this is hands down the most annoying problem this car has. Ever since I got it, I've had to deal with it. I thought I had it taken care of which gave me peace of mind for a couple of months until I looked at the big chrome bumper of the truck behind me today at a red light and noticed that my driver side brake light was not working. I've literally done everything I can think of. I'm at a total loss here, you have no idea how frustrated I am. I have brand new bulbs in both brake lights, I have them both grounded directly to the metal in the back of my trunk (which was prepped by sanding away the paint) and I have all new sockets installed (I wired in newer style sockets from an '89 Mustang into my harness). The wiring is fine, the bulb is secure and in fine working order (I looked at it as soon as I got home), there is no corrosion in the socket or in the brake light fuse location. After I did all of this, I noticed that the problem persisted, so I ook a shot in the dark and ran a completely new wire from the output on my brake light switch all the way back to my harness. Don't try telling me that I did something wrong because I know I didn't. I spent hours making sure this was done right and until today (about 3 months after the job) I haven't noticed it not working once, and believe me when I tell you that I go out of my way to check them all of the time because it's embarrassing honestly, it makes my car look like a piece of ****, and I've spent way too much damn time trying to make it look nice. Anyways, the part that really gets me is the fact that the two bulbs share the same power feed, but the first bulb that recieves the feed does not work sometimes. It can't be a grounding issue and it can't be a power issue. I really don't suspect a bulb being bad because it works sometimes and it's only three months old. The socket is fine and is not corroded at all. If anyone can help me out, I would seriously appreciate it. All I want is the feeling you get behind applying your brakes and knowing that both of your lights are coming on, like everybody else on the road. Thank you.
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How would you go about checking resistance across the brake light switch? Sorry I just realized my avatar makes my car look like it has blackout lenses but I can assure you I would never let a pair of those touch my car haha. Thanks for the help.Check the resistance across the brake light switch. Maybe you're getting too much loss across it and it will only let one lamp light, or fully light. Also check the voltage at each lamp under load. I notice you have black out lenses, so one lamp may be lit dimmer than the other and you can't see it.
I assume that there is a terminal located at the switch carrying the hot lead (from the fuse panel) and the load (to the bulbs). Disconnect the terminal and measure the resistance with an ohm meter across the contacts at the switch. It should be infinity at rest and zero with brake pressure. If it varies from that, or varies with pedal pressure, then replace the switch.How would you go about checking resistance across the brake light switch? Sorry I just realized my avatar makes my car look like it has blackout lenses but I can assure you I would never let a pair of those touch my car haha. Thanks for the help.
Okay I'll try that out after school tomorrow and I'll let you know what I get. Thanks!I assume that there is a terminal located at the switch carrying the hot lead (from the fuse panel) and the load (to the bulbs). Disconnect the terminal and measure the resistance with an ohm meter across the contacts at the switch. It should be infinity at rest and zero with brake pressure. If it varies from that, or varies with pedal pressure, then replace the switch.
So, I checked it out today, and when the brake pedal was not depressed, and the switch was closed, I got nothing on my meter, like I should have. When I depressed the pedal and the switch opened, my meter fluctuated a whole bunch between around 120-130 ohms. Any ideas?
Yeah, replace the switch.
Jump the hot lead directly to the load just to make sure. But I'll wager that when you do that both brake lights will be bright.
Jump the hot lead directly to the load just to make sure. But I'll wager that when you do that both brake lights will be bright.
Yeah I'll go ahead and replace it then. I figured that was about the only thing it could be at this point. I mean, it can't be ground, the bulb, the socket, the power feed, all the connections are good, no corrosion, etc. and it's not like it could be the power being fed to the switch or neither one of them would work, it must be the switch. I really hope that takes care of it, I can't stand wondering whether or not my right brake light is working each time I press on my brake pedal. I figured it would probably be the switch but I was hoping for a second opinion on the matter. Thanks again!Yeah, replace the switch.
Jump the hot lead directly to the load just to make sure. But I'll wager that when you do that both brake lights will be bright.
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