What would make this block of fuses go bad?

[86 911 Targa]

Originally Posted by heavysixer

Here is an update on where I am now. I ordered three bags of bullet fuses (5,8,16) and they arrived today. I decided to replace the last 10 fuses at the end of the block since they all fit nicely into the amperage range I had.

Before setting the new fuses I gently cleaned the copper terminals with a sanding block to remove the built up corrosion. However, once set my headlights and fog lamps will no longer turn on. I replaced the new fuses with the old ones but no luck. Everything is still off.

Could gently sanding the connectors have messed something up? I would have actually thought I was improving the connection.

Any help is greatly appreciated!

[GH85Carrera]

Heavysixer, I am guessing the fuses you just bought are plastic in the core. Those are OK for short term use but they are junk. The fuse gets hot and the plastic gets soft and will squish.

Try a local VW dealer. They often have the ceramic core proper fuses. They are silly how expensive they are but they are worth using.

If you stay with the plastic fuses, keep a LOT of spares in the car.

[heavysixer]

@86911Targa thank you for the wiring diagram I will double check that I have the right fuses in place.

@GH85Carrera, actually I bought all ceramic fuses here is an example:
Amazon.com: Install Bay GBC8-25 8 AMP CERAMIC Fuse 25 PACK: Industrial & Scientific

They seem to be as good as the Bussman fuses that you can buy at the auto supply store.

I tested several of the fuses for continuity and they pass, and even swapping the old fuses back still doesn't make the headlights turn on.

I have zero experience testing electrical systems so I am wondering if:
1. Lightly sanding the contacts caused an error
2. I managed to blow something else like a relay?
3. My car hates me

I noticed that with the headlights in the on position the top of the fuses block is not hot according to the test light. I would assume it would be. This seems to be true for all of the fuses that control the high and low beam circuits. I do see the interior gauges light up though so I think that means the knob itself is functioning.

Thanks everyone for the help in debugging this!

[911pcars]

The issue you have is a lack of source voltage, NOT existing fuse capacity, even if the wrong fuses are installed.

Fuses are merely current sensing elements of a circuit. If there is continuity through the fuse, it should either work to conduct circuit current or "blow" (create an open circuit) if circuit current exceeds design specs.

Use the factory electrical schematic to search and identify the source of battery voltage common to all the affected fuses. Many are related to the headlight switch and ignition switch.

Sherwood

[86 911 Targa]

^^^^^
For our '86.

pm me as needed.

Good luck,

Gerry

[Das Schnell Ei]

Originally Posted by Noah930

I had this uncommon thing happen to me once:



Could explain why simultaneously everything on that fuse block isn't working. I couldn't tell until I took all the fuses out and took the block out that it had cracked like that and couldn't maintain good springy tension across the terminals.

this is the first thing that popped into my mind .... a cracked fuse block will be a random pain in the ass, sometimes everything works , breath on it wrong or poke at it and then half of the stuff in the car stops working ...if more than one circuit in the car is giving you random issues check the back of the fuse blocks for cracks....and like others have said after you fix the main issue swap out those plastic fuses

[GH85Carrera]

Are those fuses using aluminum for the conductor? If so you likely will find the aluminum will oxidize and cause problems in the long run.

It is a pain to find ceramic core copper or brass conductor fuses. Anything else will cause problems eventually.

I tend to keep my cars for a long time. I have had my 911 for 19 years and before that a 914 for 21 years. Trust me, if you uses anything but the ceramic and copper good fuses you will be cussing at yourself down the road. BTDT.

Electrical problems never seem to happen at a convenient time.

[heavysixer]

Sherwood I am starting to agree with you. Considering the top of the fuse block is not hot I do think there is a power problem.

I tried swapping the horn relay for the fog lamp relay and the horn continued to work, so I don't think it is the relay itself.

The headlight knob turns on the interior gauge lights so I think the headlight knob also works.

I am looking for a wiring diagram now to see where the source of the voltage originates from.

Just to clarify for others reading this thread, the fuses I bough are ceramic and brass, even though the amazon listing appears to show aluminum. I even scratched the surface of one of the fuses to confirm it was not just a light coating of brass on the surface of the metal. It appears to be solid all the way through.

Additionally, I did a visual inspection of the block itself i unscrewed it from the body of the car and felt around behind it and did not feel any breaks. I could disconnect the entire thing but I don't want to break something else before I've tried to track down the lack of voltage. If I can't figure anything else out I will resort to unwiring everything and inspecting the block.

Thanks again everyone for the great images and schematics you have posted it is really helpful!

[heavysixer]

Ok so I'm an idiot (or at least mostly an idiot). As it turns out either the high beams or the low beams don't work and when the stalk is set to that setting inside the car you get no headlights AND no fog lights. I am not sure if that is normal or not though, and could be symptomatic of a larger problem.

Should you be able to run your fog lamps in either high or low beam settings (seems like you should)?

[911pcars]

Originally Posted by heavysixer

Ok so I'm an idiot (or at least mostly an idiot). As it turns out either the high beams or the low beams don't work and when the stalk is set to that setting inside the car you get no headlights AND no fog lights. I am not sure if that is normal or not though, and could be symptomatic of a larger problem.

Should you be able to run your fog lamps in either high or low beam settings (seems like you should)?

I haven't yet experienced a burned out Lo-Hi beam column switch, but I believe those are the symptoms. Do you have aftermarket headlamps and/or high wattage fog lamps (e.g. H1, H4)?

Sherwood

[Jtt84911]

May be the perfect time to replace the orig fuseblocks with the updated fuseblock panel kit...... which I and many 911 owners have done....which uses the modern two-prong push in fuses found in all current cars.

You can search this forum and see Fred Cook's panel. You can also get the headlight relays add on package with the new panel.

It's not that difficult to do.....if you are careful and take your time doing it

Regards,
JT

[911pcars]

Originally Posted by Jtt84911

May be the perfect time to replace the orig fuseblocks with the updated fuseblock panel kit...... which I and many 911 owners have done....which uses the modern two-prong push in fuses found in all current cars.

You can search this forum and see Fred Cook's panel. You can also get the headlight relays add on package with the new panel.

It's not that difficult to do.....if you are careful and take your time doing it

Regards,
JT

Respectfully not agree. Faulty fuse block? No problem. However, it's not wise to install a new fuse panel just to end up with the same symptoms. If you have to sublet repairs to a pro, they will either decline the job if an unknown aftermarket part was installed on top of the malfunction or charge you additional time to 1) confirm the upgrade was equivalent to factory spec and 2) to find and repair the original symptom.

Repair the malfunction first, then upgrade if desired.
Got a copy of the factory schematic yet? If so, grab a pencil and trace the path from the battery to the fuse block or headlight switch (I don't recall the exact current path). The headlight circuit should work with the ignition ON or OFF. Have you tried to simply tighten the circuit wire hold-down screws at each fuse position?

In my early 911, fuse no. 1 provides source voltage to the ignition switch which energizes all ignition switch-related circuits. If an open circuit occurs here, the entire ignition, fuel pump and cranking circuits are dead.

Sherwood

[fred cook]

Unless changed from the factory design, the fogs will only work on low beam. There should be a blue/white wire going from the bottom of fuse 6 that activates the fog light relay when the low beams are on and the fog light switch is pulled on. The ignition switch also has to be in the run position.

[heavysixer]

Fred thank you for the info! That explains why it works only with the high beam switch disengaged. I am going to try and take off the steering wheel and see if the high beam light is shorted now!

[fred cook]

Originally Posted by 911pcars

Respectfully not agree. Faulty fuse block? No problem. However, it's not wise to install a new fuse panel just to end up with the same symptoms. If you have to sublet repairs to a pro, they will either decline the job if an unknown aftermarket part was installed on top of the malfunction or charge you additional time to 1) confirm the upgrade was equivalent to factory spec and 2) to find and repair the original symptom.

Repair the malfunction first, then upgrade if desired.
Got a copy of the factory schematic yet? If so, grab a pencil and trace the path from the battery to the fuse block or headlight switch (I don't recall the exact current path). The headlight circuit should work with the ignition ON or OFF. Have you tried to simply tighten the circuit wire hold-down screws at each fuse position?

In my early 911, fuse no. 1 provides source voltage to the ignition switch which energizes all ignition switch-related circuits. If an open circuit occurs here, the entire ignition, fuel pump and cranking circuits are dead.

Sherwood

I agree with Sherwood. Fix the problems before changing anything you don't have to!
Unless there is a fault in the original fuse blocks, you should be able to get everything working. Good luck!