Should all fuses make test light light up in ON position?

I’m trying to figure out a electrical problem in my car and when I probe the Taillight fuses the light doesn’t light up. Car is in ON position.

Should all fuses get a reading? Looking at the fuse itself, it is not blown.

Just trying to understand if this means there is definitely an issue in the circuit of it’s normal for light not to light up.

If the ignition switch is ON but the engine is not running, all the fuses should read about 12V or the test light should glow. The switch to turn things on is downstream of the battery and the fuse.

Tail lights should be connected around the ignition switch directly to the battery so they can be turned on without the ignition being on.

I do I do believe though that the circuit needs to be energized before you will get a reading or the test light going on. If you turn the light switch on, you should get a reading, otherwise the circuit is dead, correct? The fuse is just in line downstream from the battery and then switch to power it up. Now using an ohm meter is different. You would get a reading regardless of the circuit being powered up.

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IF the circuit is powered, you should get a light ON on both sides of the fuse. If it’s not powered, it should be OFF both sides. If you get ON one side and OFF the other, the fuse is popped.

If you have OFF both sides, energize that circuit (turn the lights on, the radio on, whatever) so you get an ON indication.

If you use an ohmmeter, you can get false readings if there is any power in the circuit. In other words, only use an ohmmeter if there is no power on anywhere. You can remove the fuse and then check it with the ohmmeter.

It depends on where the fuse is located in the circuit. In most cases the fuse would be upstream of the tail-light switch, so if you placed a test light on the fuse and the chassis, it would light up when the tail light circuit was powered up (irrespective of whether the tail lights were on or not). But if the fuse was downstream of the tail-light switch, it would only test as powered up if the tail light switch was on.

Yeah I think you are probably correct. Gotta look at a wiring diagram I guess but depending on the purpose of the test, if you turn the light switch on and no tail light and no test light on, you know there is a problem. Must have been a reason for checking the fuse, huh?

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Yeah, it’s a electrical problem and I don’t know much in that. Let me explain the issue.

Out of the blue one day (which, I know things usually don’t happen like that, well I did replace my windshield but don’t see how they could have caused issue) when I hit my brakes, my parking light and interior night lights come on. Release the brake they go off. On the other hand, when I do turn my parking and interior night dash lights on, they come on as normal, and my cruise control will not set and the ESC OFF light will come up after about 5 mins of driving and not work until car is restarted. As if it thinks the brake is engaged when the lights are on? Also, my remote start doesn’t work anymore, starts up but the it turns back off after dash light flashing which probably just means the current issue is affecting the remote starter and that cannot operate properly.

Now I have no clue what to do. Since this is a beaterish car I kinda wanna learn and fix it myself but at the same time I have no clue where to start, so I did with the fuses.

Some say it could be a bad ground and I know how to check the grounds voltage and know if it’s bad, but how do I start knowing which ground could be bad or where are all the grounds in the car?

Haha, so yeah, if you have any idea or pointers I greatly appreciate!!

Remove each brake light bulb, one at a time and check if the brake light to tail light short goes away.

I don’t know much and am shooting in the dark on electrical problems, but if one circuit is affecting another circuit, you have a short someplace. Not a dead short where the fuse would blow but two wires (or inside a switch or device) that are bare touching each other, so that energizing one circuit feeds into the other circuit.

Really I’ve had both a couple times and was not able to diagnose it as a professional but found the problems by looking for problem areas plus thinking back of things that happened and linking them. So a little more crawling around looking for wires burned or devices burned etc. might help. Looking at a wiring diagram might be useful too.

At any rate back with out 61 Mercury when I was a kid I took it out of town and heard a bump and then the muffler got louder. Took it out a few days later on a longer trip and when I turned the signal light on all four lights would flash. Took it to a shop and they pulled the steering wheel off etc. and were stumped. Back home I started looking around and thinking about the exhaust noise and lo and behold found melted wires right above the resonator that I had punched a hole in. The heat from the resonator melted the wires together causing the short.

Another time on my 67 Buick hauler, I got stopped for my tail lights being out. I put a fuse in and they would be ok short trips but then would blow the fuse. It was for sale and when some kid tried it out, when he brought it back the lights were out again so I knew he warmed it up pretty good. Started looking again and found the wires above the muffler were hanging down on the muffler. When it got hot enough it would melt the wire and blow the fuse. When it was cold no problem.

So just saying you don’t always need to know what you are doing to find the problem if you are determined, take a good look, and put events together. Or pay someone.

Wow ok. It works. No lights come up, cruise works when light on, remote starter works. But how??

I did somewhat what you said, at first I took one and 2 at atime, still doing it, then I’m like F it I’ll take all 4 (there is 2 per brakelight) then the issue went away! So I’m like ok, I’ll put 1 by 1 and test every time, issue did not come back at any. Did a like 2 min drive no problems as of yet.

How?? It would have made sense if I put one back then it comes back but the issue just went away? I must say though one bulb was different, the metal at the bottom is copper instead of the other gray and says China on it which may have been a replacement bulb and it’s causing issues? If it comes back I guess I’ll replace that bulb.

A loose filament in the bulb can sometimes come in contact with the other circuit, brake/tail light. Look closely at the bulbs, check if both brake and tail light filaments are intact and working.

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Hmm ok.

Just hard to understand how it could do that since the bulb is in it’s own little lens right. Oh well.

If problems comes back I’ll take another look.

Understanding take a second place to results. Wouldn’t be the first time I didn’t understand why something worked or not.

Haha I know I know, especially electrical problems aye.

I noticed yesterday now my bottom brake light bulb is now always on so that bulb is definitely malfunctioning. I ordered a new set of bulbs.

I don’t see how a bulb defect can make it be on all the time. That is some other problem, like a relay or wiring issue.

Well, when that bulb was in the upper position it would cause my original issue, and now it only causes this in another location so… anyways I’ll just return the bulbs if it isn’t it, got them on Amazon.

Bulbs on Amazon when there are parts houses and even Walmart and now you have to pay a return fee, Why.

There’s a few reasons.

  1. Free Amazon returns, no fee, not sure what you’re talking about
  2. Going in person means I need to get out of the house
  3. I was missing a few bucks for 1 day shipping, so I’ll be getting them tomorrow anyway

Crazy light problems many times are caused by bad grounds. Bulbs then ground through other bulbs and nothing makes sense.

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