burnt wiring- thoughts?

[LEAKYSEALS951]

Smelled something burning last night. It was this.
Thoughts? Looks like this has happened before as the fuse holder had been replaced.
Thanks,
Ron

[E Sully]

Year and engine info, any modifications?

[LEAKYSEALS951]

Thanks, yes. 78 sc. Stock with exception of new msd streetfire ignition installed over a month ago. The fuse panel list this position as "fuel pump relay" but it had this 25 amp fuse which went bigtime. This fuse (and it's holder) was spliced in at some point, and (before it burnt) fit well into the round relay hole, so I don't know if it was a jury rig, or a replacement for another OEM fuse holder that blew up in the past. My google searches don't really show many pictures of a 25 amp fuse in the #2 relay position. We've got some family in town, so I haven't really had a chance to research this/dig in, but I'm assuming it's the fuel pump fuse. That sucker burnt! I'm planning on redoing my fuel lines here soon (and install a new fuel pump) so I'm gonna use this as good excuse to get that project going since it looks like I'm gonna have to trace all this stuff anyway. Haven't had a chance to test the actual fuel pump circuit/ relay yet. I was basically wondering- is this setup stock? and is this failure common?
R

[Lapkritis]

Quick glance but that wire gauge appears a bit light for fuel pump duty...

[Jdub]

Are H4 or similar halogen headlights installed without a relay? Have you noticed any weirdness with Hi/Low beams and the leftside stalk?

[irl]

Maybe someone could post a good shot of what the fuel pump relay location should look like for you. Sorry but this is my my knowledge base or I would shoot one for you although I will be embarking on heavy wiring education soon

[LEAKYSEALS951]

Originally Posted by Jdub

Are H4 or similar halogen headlights installed without a relay? Have you noticed any weirdness with Hi/Low beams and the leftside stalk?

PO had installed H4. I was unaware of the need for addl. relays- but that makes sense. I do not see any additional relays added in fuse area. Would need to pull out all carpets to make sure. Are the power to H4 and fuel pump fuse interconnected?
When you mention "leftside stalk", you are referring to the hi/low turn signal switch, right? On one occasion (just once) it did seem like a short in the contacts in the stalk prevented high beams from coming on unlesss you "held" the stalk in very sternly (as one would do if they were going down the interstate at 70 mph and all of a sudden the lights went off) I chalked it up as a bad contact. Never happened again.

[tctnd]

Heat at some point in an electrical circuit generally indicates that the resistance is excessive there. The most frequent causes are:
1. Poor connection (very common in european "pointy" fuse holders)
2. Overloaded circuit (see above queries re lights, extra components etc.)

[LEAKYSEALS951]

Here's a better pic of the "splice" in of a newer style 25 amp ato fuse. The original #6? location european fuse has the fuse but no wires. The wire gauge of the splice in seems equivelent. Also,the contacts in this car are immaculate! (well at least compared to what I am used to...)


FWIW: I am tempted (once I find out/rectify what CAUSED this) to abandon the ATO fuse location, remove the splices, and go back to the original fuse location. It certainly would be the easiest fix, unless the ATO works that much better. Did people abandon the european fuse for the ATO in the fuel pump fuse for reliability? Just curious.

[javadog]

Obviously, that is not stock. People put crap like that in because they are too cheap to fix it the correct way, or clueless.

Since I don't own the car or know it's history, I can't say which of the reasons might be the real one. Let me speculate as to what happened. The original fuse holder lost a little tension. This could be from resistance caused by corrosion, followed by an increase in temperature when the car was run. It's also possible that the fuel pump is getting old and perhaps drawing more current than it should. Once the fuse holder loses tension, there's a little cycle of less tension=more heat, etc.

The fuse box is made up of several sections of fuse holders of differing lengths. These are replaceable. My suggestion would be to replace any that you feel might have a problem. Or, you could try cleaning all of the contacts and replacing any fuses that look suspicious. Beware, there are aftermarket fuses that are essentially crap and you don't want to use those. Testing the amperage draw of the fuel pump is also not hard to do. There are specs for the maximum permitted draw.

You might also check that all of the fuses are the correct size for each circuit.

JR

[LEAKYSEALS951]

Originally Posted by javadog

Obviously, that is not stock. People put crap like that in because they are too cheap to fix it the correct way, or clueless.

Since I don't own the car or know it's history, I can't say which of the reasons might be the real one. Let me speculate as to what happened. The original fuse holder lost a little tension. This could be from resistance caused by corrosion, followed by an increase in temperature when the car was run. It's also possible that the fuel pump is getting old and perhaps drawing more current than it should. Once the fuse holder loses tension, there's a little cycle of less tension=more heat, etc.



JR

That's what I don't understand. To me, the original fuse box is in really good shape (see closeup). That's why I was wondering if this was a common thing to "improve" the fuel pump fuse or just something that this one owner did. I can't see any reason to abandon the present fuse panel based on it's condition.Perhaps the original fuse panel sucked, the owner rigged the ato fuse, then somebody else replaced the fuse panel to the current immaculate fuse holders. Who knows...

[javadog]

It might look fine but that doesn't mean it wasn't a problem. A fuse can make poor electrical contact before you see any visible corrosion products. The tension problem isn't something you'll see just looking at it. You'd have to install a fuse and see how it feels.

Either way, the "upgrade" has to come out, so you'll have to decide which course of action you pursue for the repair.

JR

[LEAKYSEALS951]

Hey folks,
Thanks for the help with the fuse. The "upgraded" ato fuse 25 ampendectomy was a complete success and the after going back to the original fuse panel, the car starts better than ever. After studying the filament on the 25 amp fuse (it didn't burn out), i am guessing the melting occurred due to a short between the fuse and the copper connector, or a potential worn through short between the wiring and the fuse box itself.

After reading up on the fuel pump relay itself, i think i have a pretty good idea of how it works, especially after reading this thread:

Why is red fuel pump relay special?

But i did have one question. In the wiring diagram, It appears that both the air meter and something called a "speed switch" ground out pin 85 on the fuel pump relay, but what/ where exactly is the "speed switch", or am I reading the wiring schematic wrong? forum searches, google searches, and cis primer searches pulled up nothing on a "speed switch". I'm just curious.

Thanks.
Ron

[timmy2]

Speed switch is the rev limiter in US cars, euro cars used a rev limiting rotor. Your MSD probably covers that aspect. Is your car a US '78 or ROW? Speed Relay should be on the rear fuse panel for US car.


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[T77911S]

25 is too big. put in a 15.

i would also check the current that the FP is using. i think my 77 was only using about 7amps.

[darrin]

back to your headlights -- the reason you want headlight relays is that, as delivered from the factory, all the headlight current runs through both your headlight switch and the high/low beam switch on the turn signals. With std. sealed beam headlights, this can be a bit much (my turn signal switch contacts became misaligned due to the heat in the contacts softening the contacts, which caused me to randomly flash folks with my high beams (not fun).

Since h4 conversions frequently utilize even higher wattage bulbs, this compounds the problem. Adding a relay (our host sells a turnkey kit by jwest) turns the headlight switch and turn signal into triggers and keeps the current away from these. AS an extra benefit, by limiting the high current circuit, your headlights may well get brighter too.

[johngypsy]

here you guys go, click on this link hope this helps

930 Fuel Pump Fuse Overload - The Solution - Pelican Parts Technical BBS

[pors1968]

one year old .