Headlight fuse #2 keeps blowing

[OldRoller]

If you are using a digital volt/om meter or digital probe to check your systems, the results can be misleading. These devices can measure very small resistances and indicate a ground when in reality it is measuring the path through bulb filaments, led circuit boards, motor brushes, etc.

Best use an incandescent test light to verify the path. If there is a ground the bulb will pull enough current to light when the test light cable is connected to battery positive. Car positive cable disconnected from battery, negative must be connected. 

 

Reading back to your original #2 fuse issue I missed the LED install. It is possible that your original fault was a shorted LED bulb housing. On more than one occasion I have had LED's that short internally and create havoc, working intermittently or blowing fuses, especially since most are cheaply made. 

Remove all your Led bulbs and recreate the scenario. Rule out a bulb/housing/wiring issues with the lights first.

Edited January 8 by OldRoller

[Ral]

Thanks Sparkie.  Very helpful information on knowing what is what.  

 

I have been checking the right side (high side) of the fuse box.  Since I'm concerned the solid red wire from the battery is somewhere grounded I have been testing circuits with the battery disconnected and using my multimeter in continuity mode.   When. the red (+12) is connected to the right side of #7 circuit in the fuse box I show it being connected to ground at the battery and also at the ignition switch.  If I disconnect the red wire from the fuse box both ends of the solid red wire at the battery and ignition switch are no longer grounded.  Also the now disconnected red wire connected to #7 is not grounded.  This leads me to believe that something in the fuse box is grounding out the #7 circuit and also other circuits.  But after reading your explanation on the headlights, I should expect those circuits to show some continuity. 

I find it hard to believe the fuse box is somehow shorted and tying circuits together.  I'm going to disconnect the high side of 7-12 and see what it shows for continuity across those circuits and then start to trace the other circuits without lights to see what I can find.    

 

Thanks all for the help.  I will be driving this car again soon.  :-)

[John76]

29 minutes ago, Ral said:

 When. the red (+12) is connected to the right side of #7 circuit in the fuse box I show it being connected to ground at the battery and also at the ignition switch. 

Ral,

Is your key still in the ignition switch?

Did you check the ignition switch with a load (incandescent bulb as recommended by @OldRoller)

 

Attached sketch is for a '74-'76 car.

Your Green wire from the ignition switch (#15) goes to fuses #9, #10, and #11 (all linked).

Your Violet wires from the ignition switch (R) go to fuse #12, and to the plug for the radio. Is your radio still connected???

 

[Ral]

Thanks John76.  I somehow missed the steps that OldRoller suggested.  I have since gone back and removed all LED lights (all tail lights, front turn signals, license plate) from the circuit.  Also learned that I do get a ground reading on # 2 & #3 when the headlights are connected so this validates a previous comment that current flows through the filament of the bulb to ground.  Never thought of that before.  I'm going to go check the ignition switch next.  I did find that the Red / white wire on #8 going to the hazard switch is grounded.  I think this might be the part of the problem.  When I remove that wire, fuse box #7 & #8 are no longer grounded.

 

I'm also going to check the LED lights with a multimeter.  Just reading on how to do that if it has a diode setting.  Also noticed that the previous owner put in a special blinker relay that supports LEDs.

 

Class is still in session on this problem.

[OldRoller]

Ral, when you are checking, are you using the multimeter? In what scale? What reading in ohms are you getting when testing the red/white wire from #8 to the hazard switch? 1 ohm? 10K ohm? 1M ohms? Grounds on our old cars are best tested with a test light connected to battery positive.

I know this car is new to you. Did it arrive running and some functions worked? Or was is a non functioning 02 with many systems inoperable? Battery in good nick? Was it connected when you began this episode? You may be running down a rabbit hole with no evident bottom. Very highly unlikely that the solid red from the battery to fuse panel/ignition switch was grounded. If so you would have found wiring burnt and the magic smoke released. Reassemble your circuitry and determine what works and what doesn't. Check all fuses (for 12v on both end clamps) and narrow your focus on what doesn't work.

If your led lights are the standard base models. simply ground the base and apply 12v to the terminals. They will either work or they won't. 

 

[Ral]

Yes using a digital multimeter but only in continuity mode and to check voltage.  I have owned the car for a couple of months now and for the most part it was working.  Fixed odometer and interior light and was chasing the dash cluster lights not working when #2 fuse started blowing. I have a suspicion that an LED light was causing that problem and will know once I test them out.  Battery is good and located in the trunk.  Positive from the battery runs behind the back seat, along the left side to a terminal block mounted on the firewall.  Battery negative is terminated on the back wall of the trunk.

The red wire ground was a result of hazard wire circuit that appears to be grounded but need to spend more time with that one.  

I'm going to test the LEDs and then test the ignition switch voltage.  If all  looks good then spend more time with the hazard circuit before I put this all back together and see what the new symptoms are.

Funny story, last night when I was hooking up the battery again to test a circuit as soon as I connected it the horn started to go off.  I had to laugh at the yet another electrical issue I had to deal with.  Turns out the horn wire connection grounded out as a result of me playing under the dash.  I'm enjoying the adventure but I'm ready for it to be behind me.   

Thanks all for the help.  At the end of this I have a much better understanding of the car.

[Ral]

Making some serious progress.  Seems like the instrument cluster is the one that is overloading the #2 circuit.  I hooked all lights up and the instrument cluster and everything was working for a bit and even had instrument lights working but it didn't last long until the fuse blew again.  Removed the driving lights from the circuit and was pegging the meter in the 600ma scale.  It wasn't until I remove the instrument cluster from the circuit that I was able to not blow a fuse.  With just the driving lights on, the #2 circuit was drawing 500ma.  All driving lights are LED lights.  I did upgrade the instrument cluster lights to 5w from the original 2.5w.  This in combination with the LED lights might be over loading the circuit.  I need to look closer at the instrument cluster to see if there is a short on the lighting circuit board.   Go figure that the original objective was to get the instrument cluster lights to work so I could see the instruments while driving at night.  In the process of working on the instrument cluster I replaced all the lights to a higher wattage so it could be brighter.  The reostate that dims the instrument lights doesn't seem to be working but at this point I don't care. Ignition switch seems to have the right voltages in all positions also.

[OldRoller]

Nice! Driving lights at half an amp and instrument bulbs won't blow the #2 fuse on their own. Sounds like you have an intermittent short in that circuit. I assume you have the driving lights wired straight off the #2 fuse and not a relay? Disconnect the driving lights and see if the dash causes the fuse to blow. No? Swap circuits - dash off, driving on. Or disconnect both and rule out anything else on the car. Keep at it!

 

[Ral]

Final chapter (maybe).  Spent time with the instrument cluster today and didn't find a short.  Decided to add a ground to the cluster as per a previous posting and installed the cluster.  My reading through the #2 fuse was 500 m amps without the cluster and with the cluster installed I pegged the meter at 600 m amps.  Need a new meter with a larger scale.  Decided to live on the edge and went from a 5 amp fuse to an 8 amp fuse and it held.  I've ordered a new meter so I can know for sure what it's drawing but I have dash lights and running lights working again.  With hindsight I should have focused on the component (instrument panel) I was working on instead of chasing the rabbit.  On the bright side I learned an awful lot about the wiring, LED lights, and what I can do to improve the headlight circuit.  Thanks all for the help.  Now that it's running again of course it's raining.   Love this car.  I had one in high school in the 70's and it feels like I'm 18 again in my mind.  My body says otherwise but the mind is what counts until you get out of bed.

[jimk]

2 hours ago, Ral said:

My reading through the #2 fuse was 500 m amps without the cluster and with the cluster installed I pegged the meter at 600 m amps. 

Could be that one of the circuits that passes thru the cluster is causing the current draw and not the cluster.

[OldRoller]

Glad you have it to this point! The load of 500 milli amps (one half of an amp) is not much of a current load. And another 100 milli amps (or one tenth of an amp) is to be expected from modest cluster operation. You now have an 8 amp fuse protecting the circuit, capable of handling 8000 milli amps plus a small percentage. Not to worry, a dead short to ground or a failed component, should you have one, will make short work of the 8 amp fuse. 

Points:  1. you have tackled an issue and bested it.   2. You know more know about the workings of your 02.  3.You still love your 02!

4. You're still 18 in your mind! The body will just have to catch up....

Well done Ral!

[Ral]

Thanks for the milli amp to amp conversion.  Once I get the new meter I will know if I can go back to the 5 amp (5000 milli amp) fuse.  I had a good laugh with Points 1-4.  Thanks again for all the help.  

[Mike Self]

6 hours ago, Ral said:

Decided to live on the edge and went from a 5 amp fuse to an 8 amp fuse and it held. 

Uh...IIRC all the fuses on a 2002 are either 8 or 16 amp.  Someone correct me if I'm wrong, but I don't remember a 5 amp fuse in the system...perhaps that's been your problem all along, especially if you have driving lights wired through that fuse.  Even LED driving lights draw a bit of current...

 

mike

[02Les]

FWIW - Fuse sticker/decal for 1971

[Mike Self]

Les, you're absolutely correct--for 12 fuse cars...I was thinking 6 fuse cars where the fuses are all 8 or 16 amp.  However, if Ral has his fog lights wired directly through fuse 2 with out a relay, that's probably enough amperage to pop a 5 amp fuse...

 

mike