Electrical Headlight fuse blows

[cglax6]

Painless wiring harness complete. Started testing circuits and 30a headlight fuse blew when I pulled the headlight switch. Switch is brand new.

I don't claim to be an electrical guru, but I can follow directions and didn't stray from what the Painless manual said to do.

I also have new Speedhut gauges (speedo, oil, volt) and they're wired correctly.

From what I understand, if I'm blowing a fuse, that means there is too much on the circuit or there's a short. Besides the Speedhut gauges, all of my lights are the same.

That leads me to believe that it's a short somewhere.

Could my new OMIX switch be the culprit? I have my old switch and can put that back in.

Besides a cut wire somewhere touching something that it shouldn't, what else would cause a short?

I need to get a test light tomorrow and start removing bulbs to track it down.

Any other advice or recommendations out there?

Thanks for your help.

 

[shum8]

Swapping the switch would be an easy way to rule the new one out......


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[cglax6]

Swapping the switch would be an easy way to rule the new one out......


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Very true...just trying to prepare myself for worst case scenario. I don't have any more 30a blades hanging around, so I need to grab a few tomorrow...figured I'd grab a test light too.

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[shum8]

I’m assuming you swapped out the switch at the same time the new harness went in? Gotta start ruling stuff out somewhere..... If you blow another with the old switch, then yes, there is a short somewhere. Unfortunately, that won’t be the fun part....


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[cglax6]

Yeah, that's what I figured. Would it be best to pull bulbs one at a time to narrow down location of the issue before tracing individual wires?

And yes, I put a new switch in with the wiring install. Not sure why...the old one worked just fine.

My gut is telling me it's either the switch or how the Speedhut gauges are wired.

I inspected every single wire before and after running everything to prevent trying to find a cut wire somewhere.

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[shum8]

Disconnect the gauges and reinstall the old switch. If that blows the fuse, deep digging lies ahead. If that doesn’t blow a fuse, swap switches. If that doesn’t blow it, the you’ll have your source of irritation.


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[cglax6]

Oh goody! I can't wait[emoji1787][emoji1787]

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[shum8]

I love being the bearer of good news..... hopefully it will be the switch.


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[cglax6]

I hope so, then LG can chastise me for buying OMIX [emoji1787][emoji1787]

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[shum8]

[emoji1787][emoji1787][emoji12]


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[CJ]

Painless wiring harness complete. Started testing circuits and 30a headlight fuse blew when I pulled the headlight switch. Switch is brand new.

I don't claim to be an electrical guru, but I can follow directions and didn't stray from what the Painless manual said to do.

I also have new Speedhut gauges (speedo, oil, volt) and they're wired correctly.

From what I understand, if I'm blowing a fuse, that means there is too much on the circuit or there's a short. Besides the Speedhut gauges, all of my lights are the same.

That leads me to believe that it's a short somewhere.

Could my new OMIX switch be the culprit? I have my old switch and can put that back in.

Besides a cut wire somewhere touching something that it shouldn't, what else would cause a short?

I need to get a test light tomorrow and start removing bulbs to track it down.

Any other advice or recommendations out there?

Thanks for your help.

If the fuse blows immediately it is a direct short. Now, have to say don't just get a crappy test light, spend a few more bucks (or a small amount) an get a DVM or a meter.

Stop blowing fuses - it gets expensive an is not working. Use the meter to check each circuit to ground (continuity) and then each circuit.

A TEST LIGHT WILL NOT DO THIS.

Set the meter to ohms an see if you have an open circuit (good) or a closed circuit (bad).

 

[cglax6]

If the fuse blows immediately it is a direct short. Now, have to say don't just get a crappy test light, spend a few more bucks (or a small amount) an get a DVM or a meter.

Stop blowing fuses - it gets expensive an is not working. Use the meter to check each circuit to ground (continuity) and then each circuit.

A TEST LIGHT WILL NOT DO THIS.

Set the meter to ohms an see if you have an open circuit (good) or a closed circuit (bad).

The lights turned on and then the fuse blew immediately afterwards.

I have a multimeter. If there's a simple way to explain what I need to do to check continuity, I'm all eyes and ears. If not, I'll be researching tonight.

I'm a mechanical engineer...I get the basics of wiring and electricity...just not experienced in chasing down a short.

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[Masscj7]

Usually continuity is the ohm/resistance setting in the meter, you might have to change the mode.

Most meters when on continuity will give you a tone when you touch the two leads together. You can then put one lead to ground/chassis/body and then test the output side of the switch without turning it on. This will tell you if your circuit is grounding out. One side of your switch will also be correctly ground.


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[Masscj7]

You can use continuity to test for blown fuses without pulling them. Very quick to go to each fuse and touch tabs on the tops of the fuse. If you have tone, an intact fuse. No tone, probably blown. Now this isn’t an absolute. Many times I’ve seen fuses hair crack and they’ll pass continuity, but if you actually test them with dc voltage, you’ll see one side usually 11-12volts and the other side much less than that. It’ll pass continuity tone to appear not blown, but won’t pass enough voltage to power the circuit. But we’re getting away from the question at hand of how to find something shorted to ground.


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[cglax6]

Just want to make sure I'm understanding correctly...

To test for a short somewhere (assuming my new switch isn't the culprit), put one lead to ground, and then one lead on an output wire on my headlight switch (or whatever part of the headlight circuit that I need to test). If I get a tone, then that individual circuit is good and I can move on to the next?

If I don't get a tone, that means that circuit is bad, and then I'd have to trace that particular one down and find out where the short is? Besides frayed wire, what would I be looking for?



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[CJ]

Usually continuity is the ohm/resistance setting in the meter, you might have to change the mode.

Most meters when on continuity will give you a tone when you touch the two leads together. You can then put one lead to ground/chassis/body and then test the output side of the switch without turning it on. This will tell you if your circuit is grounding out. One side of your switch will also be correctly ground.


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You can use continuity to test for blown fuses without pulling them. Very quick to go to each fuse and touch tabs on the tops of the fuse. If you have tone, an intact fuse. No tone, probably blown. Now this isn’t an absolute. Many times I’ve seen fuses hair crack and they’ll pass continuity, but if you actually test them with dc voltage, you’ll see one side usually 11-12volts and the other side much less than that. It’ll pass continuity tone to appear not blown, but won’t pass enough voltage to power the circuit. But we’re getting away from the question at hand of how to find something shorted to ground.


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Wow, this is why we have great members.

 

[Masscj7]

Just want to make sure I'm understanding correctly...

To test for a short somewhere (assuming my new switch isn't the culprit), put one lead to ground, and then one lead on an output wire on my headlight switch (or whatever part of the headlight circuit that I need to test). If I get a tone, then that individual circuit is good and I can move on to the next?

If I don't get a tone, that means that circuit is bad, and then I'd have to trace that particular one down and find out where the short is? Besides frayed wire, what would I be looking for?



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Well, in theory, depending on what your testing for, tone could be good. Let’s use example of speaker wires. Say you have a speaker not playing. If you have the wires at the speaker location and behind the radio available, you can cross your wires at the speaker location and put your meter on each lead behind the radio, if you have tone you know you have continuity across both wires. If no tone you have a break.
If possible break, now have to meter the wires individually. Use a long piece of wire or I have long alligator clip leads, clip one lead to one side of speaker wire and other lead behind radio, if tone, wire is intact, no tone, wire is broken. Another scenario, very very common in 90’s XJs, the speaker wires break in the front door boots. To test, one wire lead to ground, and then start testing your speaker leads one at a time. If you get tone, you know a wire is grounding out or shorting to ground. So if you ever have an aftermarket radio that powers up, changes stations, plays CDs, just no audio output it’s almost always a wire or speaker terminal grounding out and sending the internal amp in the radio into protect. Remove the grounding out wire and amp comes right back on.
So back to your scenario, if we’re testing to see if we have your output side of the switch (or +12 volt output) is shorted to ground, tone would be bad.
One thing I don’t know without looking is how to make sure that you try to isolate the wire lead, meaning disconnect/isolate from the switch. There is possibility that the circuit would rest at ground when connected or it might rest at open. If resting at ground, you’d have a false reading of shorted to ground.
You could always bench test the switch with a 12v battery and a meter too. I’ll see if I can drag my switch out of the attic to see what it looks like.


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[cglax6]

Quick update. Tested the headlight switch and dimmer switch on the floor. They are both good.

Checked continuity of the wires going to the headlight switch. Found a short on the white wire which is power to the parking lights and tail lights.

How do I go about testing each wire at this point? Do I go to the bulb side and check continuity that way? Find the culprit and then trace the wire looking for the fault?

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[cglax6]

Narrowed it down thanks to some coaching from Masscj and Painless tech support.

Turns out I had spliced a hot wire from the front passenger side parking light to ground. I must not have been paying attention and thought it was a ground wire and forgot that those lights ground through the housing to the front clip. Oops!

Thanks for all the help and ideas. Thankfully I didn't have to search for pinched wires.

I removed the extra wire splice, insulated it with heat shrink and hooked everything back up. All tests SAT.

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[shum8]

Good deal!! Glad it wasn’t hiding 4 hours in.....


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