Park / tail lights fuse keeps blowing

[wil84911]

Just happened (edit: prob inaccurate as it may have happened longbefore I started using the park lights. See resolution on post #34) . As soon as the fuse touches the box it lits then blows. Haven’t touch anything electrical except pull the radio out which wasn’t even connected and that was a week ago. Checked the wiring behind the radio but saw nothing that would cause shorting. Could someone kindly provide some clues? Thanks in advance.

 

 

12/71 2.6 block E88 heads triple weber 3/2 Mallory Abarth Tokico 1-3/4 sways

 

 

 

 

[JSM]

I'll start with the obvious, no ill will intended, you have the correct amperage fuse installed correct?

And this condition happens regardless if you turn the parking lights on?  And your isolating to the parking lights on only, not stepping on the brake pedal?

Edited October 24, 2017 by JSM

[wil84911]

I'll start with the obvious, no ill will intended, you have the correct amperage fuse installed correct?

And this condition happens regardless if you turn the parking lights on?  And your isolating to the parking lights on only, not stepping on the brake pedal?

 

It’s okay. I thought about that too. Got the correct 20A but it was blowing right after getting on the fusebox.

 

 

12/71 2.6 block E88 heads triple weber 3/2 Mallory Abarth Tokico 1-3/4 sways

[Mikes Z car]

My 240Z (early 1970 model) uses a 20A for the parking/tail lights.  I think I remember that if the 32V rating is on one end of the fuse the amp rating is on the other end and can be hard to read in my experience.  So if one end says 32V the other end should say 20A.

Edited October 25, 2017 by Mikes Z car

[wil84911]

My 240Z (early 1970 model) uses a 20A for the parking/tail lights.  I think I remember that if the 32V rating is on one end of the fuse the amp rating is on the other end and can be hard to read in my experience.  So if one end says 32V the other end should say 20A.

Thanks.. checked and updated my reply.


12/71 2.6 block E88 heads triple weber 3/2 Mallory Abarth Tokico 1-3/4 sways

[JSM]

So with the lights off, you put the fuse in and it blows? Have you turned the switch on and off a few times to make sure it's not shorting somehow internally? 

Sounds like you have a grounded short if it's not in the switch. I'm assuming you've been driving it with the lights on at some point  since you've got it and this just started. 

Aside from the radio you didn't mess with the fuse block in anyway and no lose wires running up under the fuse block?

[wil84911]

So with the lights off, you put the fuse in and it blows? Have you turned the switch on and off a few times to make sure it's not shorting somehow internally? 
Sounds like you have a grounded short if it's not in the switch. I'm assuming you've been driving it with the lights on at some point  since you've got it and this just started. 
Aside from the radio you didn't mess with the fuse block in anyway and no lose wires running up under the fuse block?

Yes lights off she blows . And yes I’ve drive it with lights working fine to this point. Haven’t mess with anything yet. Still checking around the fuse block but haven’t found anything though I suspect problem may be there. Thanks


12/71 2.6 block E88 heads triple weber 3/2 Mallory Abarth Tokico 1-3/4 sways

[SteveJ]

Why do you expect the problem is around the fuse block? 

In electrical troubleshooting, the first thing to do is isolate. In this case, remove the cover from the steering column and disconnect the 6 wire connector on the headlight switch. Use a test light across the fuse and see if it lights up. If it does, continue troubleshooting.

Let's follow your hunch about the fuse block. Disconnect your battery and remove the block. Look for debris that could touch the inner side of the fuse to the chassis. If you don't see anything there, it's likely in your dash harness.

If it's the dash harness, chances are that the green/blue wire has been chafed somewhere or someone tapped it as a continuously hot source. (Think aftermarket radio here.) Where the wire was tapped may have some bare wire that is coming into contact with the chassis or dash frame.

[wil84911]

Why do you expect the problem is around the fuse block? 
In electrical troubleshooting, the first thing to do is isolate. In this case, remove the cover from the steering column and disconnect the 6 wire connector on the headlight switch. Use a test light across the fuse and see if it lights up. If it does, continue troubleshooting.
Let's follow your hunch about the fuse block. Disconnect your battery and remove the block. Look for debris that could touch the inner side of the fuse to the chassis. If you don't see anything there, it's likely in your dash harness.
If it's the dash harness, chances are that the green/blue wire has been chafed somewhere or someone tapped it as a continuously hot source. (Think aftermarket radio here.) Where the wire was tapped may have some bare wire that is coming into contact with the chassis or dash frame.

Just guessing as I remember getting a spark pulling the radio out (yes aftermarket). I will try your suggestions. Thanks


12/71 2.6 block E88 heads triple weber 3/2 Mallory Abarth Tokico 1-3/4 sways

[JSM]

9 hours ago, SteveJ said:

Why do you expect the problem is around the fuse block? 

In electrical troubleshooting, the first thing to do is isolate. In this case, remove the cover from the steering column and disconnect the 6 wire connector on the headlight switch. Use a test light across the fuse and see if it lights up. If it does, continue troubleshooting.

Let's follow your hunch about the fuse block. Disconnect your battery and remove the block. Look for debris that could touch the inner side of the fuse to the chassis. If you don't see anything there, it's likely in your dash harness.

If it's the dash harness, chances are that the green/blue wire has been chafed somewhere or someone tapped it as a continuously hot source. (Think aftermarket radio here.) Where the wire was tapped may have some bare wire that is coming into contact with the chassis or dash frame.

That may have been my fault Steve.  Since it was fine until he pulled the radio, I was thinking he might have gotten a lose wire, coin or something under there.

Wil, do everything Steve says.  He's the Picasso of electrical gremlins around here.  I'm still in kindergarten drawing stick figures!

Edited October 25, 2017 by JSM

[wil84911]

That may have been my fault Steve.  Since it was fine until he pulled the radio, I was thinking he might have gotten a lose wire, coin or something under there.
Wil, do everything Steve says.  He's the Picasso of electrical gremlins around here.  I'm still in kindergarten drawing stick figures!

Thanks folks. Appreciate the help so far. Kinda feel I didn’t leave the aircooled Porsche forum


12/71 2.6 block E88 heads triple weber 3/2 Mallory Abarth Tokico 1-3/4 sways

[SteveJ]

25 minutes ago, JSM said:

That may have been my fault Steve.  Since it was fine until he pulled the radio, I was thinking he might have gotten a lose wire, coin or something under there.

Wil, do everything Steve says.  He's the Picasso of electrical gremlins around here.  I'm still in kindergarten drawing stick figures!

Keep in mind that I know a lot about troubleshooting because I've done enough things to cause trouble, whether it was in my cars or in my projects at work.

[Dave WM]

One trick you may use is to wire in a 12v light in place of the fuse that keeps blowing. If it lights brightly, you have a short. You can then move wires around and see if you can find the issue. Move the wires around that you suspect. Disconnect the battery anytime you are messing with the fuses or connecting the test light (I use insulated alligator clips). One slip while installing fuses or hooking clips up can result in a blown fuse.

[wil84911]

One trick you may use is to wire in a 12v light in place of the fuse that keeps blowing. If it lights brightly, you have a short. You can then move wires around and see if you can find the issue. Move the wires around that you suspect. Disconnect the battery anytime you are messing with the fuses or connecting the test light (I use insulated alligator clips). One slip while installing fuses or hooking clips up can result in a blown fuse.

Fuse lights up then blows with lights off key off. Same thing right? There’s definitely a short somewhere.


12/71 2.6 block E88 heads triple weber 3/2 Mallory Abarth Tokico 1-3/4 sways

[Dave WM]

yes but with the light on you can monitor the testing with less risk to the existing wiring. the light introduces resistance to the circuit and protects the wiring from constant loads (at least until the fuse blows). The light will be on but the brightness will vary as you turn things on and off and hopefully enough of a change in brightness for finding the short.

[Dave WM]

One more thing, you may want to remove the access panels and take a look at the tail light sockets and wiring, IIRC have read about issues with shorts back there.

[SteveJ]

Just now, Dave WM said:

One more thing, you may want to remove the access panels and take a look at the tail light sockets and wiring, IIRC have read about issues with shorts back there.

Those would not come into play with the switch off. The OP said he messed with the radio before his problems started. Considering the circuit has constant power, it would be tempting for someone to tap into that circuit for the memory functions of the radio. The fact that the radio was touched recently makes that area a prime suspect.

I hope the OP will follow the troubleshooting in post #8 and let us know the results. If more diagnostics are required at that point, it can be performed in a measured approach instead of shotgunning ideas.

[wil84911]

Awesome! Might take me awhile but will certainly report findings.


12/71 2.6 block E88 heads triple weber 3/2 Mallory Abarth Tokico 1-3/4 sways

[Dave WM]

Oh ok, I remember my brake lights (I was thinking brake lights, not sure if that is the same as "parking" lights) being active regardless of key on or off. my bad.

I also see the tail lights are not hot (+ goes thru switch under pedal, ground is continuous, I am used to seeing the ground be the switched circuit) unless the brake switch is activated. oh well.

ha timely post one of my brake lights is burned out!

Edited October 25, 2017 by Dave WM

[SteveJ]

Both the brake lights and parking (aka running) lights have constant power.  Neither depend upon the key being in the On or Start position to operate. They are on completely different circuits, though. 

Again, diagnostics were posted to isolate the problem. Once those results are known, then we will know whether the problem has an easy fix or more diagnostics are needed.

[David F]

I have a similar issue:  I have spent the last couple of months bringing my '72 back to life from a long slumber.   When it came time to check all the lighting, I noticed none of the running lamps worked at all.  Checked fuse...yep, blown.  Replaced fuse without it blowing (20A, switch off).  But, turning the light switch to position one produced no light and the fuse becomes too hot to keep a finger on the terminal (but fuse did not blow).  I traced the green/blue wire to the right side firewall junctions and get continuity to three wires at the junction block with the green/blue wire.  One of them is a large gauge red wire.  I don't think this is correct, so I need to start at the switch which I will do tonight.  Will remove the switch and confirm it behalves as indicated on the wiring diagram.

Any other suggestions?  Might help both me and the OP.

Incidentally, I removed the fuse block and it is perfect...no loose connections or discolored (from heat) terminals.  Headlights work, dimmer does not (might be relay...need to check that, or switch...will check when checking combo switch).

[SteveJ]

5 hours ago, David F said:

I have a similar issue:  I have spent the last couple of months bringing my '72 back to life from a long slumber.   When it came time to check all the lighting, I noticed none of the running lamps worked at all.  Checked fuse...yep, blown.  Replaced fuse without it blowing (20A, switch off).  But, turning the light switch to position one produced no light and the fuse becomes too hot to keep a finger on the terminal (but fuse did not blow).  I traced the green/blue wire to the right side firewall junctions and get continuity to three wires at the junction block with the green/blue wire.  One of them is a large gauge red wire.  I don't think this is correct, so I need to start at the switch which I will do tonight.  Will remove the switch and confirm it behalves as indicated on the wiring diagram.

Any other suggestions?  Might help both me and the OP.

Incidentally, I removed the fuse block and it is perfect...no loose connections or discolored (from heat) terminals.  Headlights work, dimmer does not (might be relay...need to check that, or switch...will check when checking combo switch).

It doesn't sound like anything the OP is experiencing. You need a different set of diagnostics, similar to what Dave WM described in post #15. Buy a test light and post back when you have it.

[David F]

Thanks, but I don't need a test light to show/tell may anything that my VOM won't tell me.   And, a fuse that blows and a fuse that gets too hot are very similar...both are drawing too much amperage.  Why might be the difference.  I just need to trace each circuit feed by the the running light fuse.

I have verified my combo switch works as it should and I got the mechanicals of the dimmer switch working properly.

[SteveJ]

2 hours ago, David F said:

Thanks, but I don't need a test light to show/tell may anything that my VOM won't tell me.   And, a fuse that blows and a fuse that gets too hot are very similar...both are drawing too much amperage.  Why might be the difference.  I just need to trace each circuit feed by the the running light fuse.

I have verified my combo switch works as it should and I got the mechanicals of the dimmer switch working properly.

You don't even know what your meter is telling you. That is obvious from your first post. You don't even know the difference between a dead short and an overloaded circuit. What you're lacking in knowledge, however, you're making up with attitude.

If you want to drop your attitude and learn how to diagnose your problem, let me know. There are reasons for the instructions I give, and I don't necessarily explain them fully. Then again, I don't need to. 

[David F]

Tell me again who has the  attitude?  I know how to use the meter.  Thanks anyway.  I wanted help, not arrogance.  Not sure how you came to your conclusion from my first post.  Obviously you are not the one to help me.