Return Fuel System Electrical Issue (melted fuse)

[DSG2003Mach1]

Hoping to have time to chase it down this weekend but looking for input

I have a lethal return system in my Mach, been in for years. Last night I went to the trunk to pull the pump fuses so I didn't have to listen to them with the key forward. One of the fuse holders (20 amp fuses) the back side of the holder was melted. The yellow plastic around the fuse was basically gone. The fuse itself was brittle but intact enough to pass voltage. I pulled the other fuse and once I got it into the light you can see the yellow plastic was deformed as well.

The car has had no issues running or anything.

My question is what makes a fuse melt like that without popping? Will a rub/short do it or what?

I have 2 new fuse holders on the way that look identical to the ones supplied by Lethal. My kit is older so while it has the relays and such I dont believe it has the inline fusable links and such of the newer versions

 

[CobraSam]

Loose connections will cause heat issues. Perhaps the brackets that hold the actual fuse spades were a bit loose.
Also, over current will also cause heating issues. But I doubt that would be your issue since the Lethal kit comes with correct conductor sizing and fuses.
I’d check the complete wiring for any insulator breakdown where arcing or shorting could occur, like chaffing wires. Also, check all of the connections. Otherwise, install those new fuse holders and see what happens.

 

[Bullitt1448]

Concur with the above, very likely a poor connection at the fuse, could be the holder was worn or there was some corrosion happening. Replace the holder, check and monitor the wiring and you should be fine

 

[DSG2003Mach1]

Thanks guys, that's kind of what I was thinking. I'll pull the trunk liners and check for anything obvious then I'll just replace em and monitor closely. I found the replacement holders on amazon (same exact ones) for $14/pair.

 

[JaCobro]

High resistance causes heat in circuits. I.e loose connections, and/or corrosion.

 

[Slow 99]

like everyone above said...bad connection or corrosion. If you dont feel comfortable running that harness anymore, lethal just came out with "the box" and it's a (in my opinion) better version of the fore innovations controller. I was going to buy the box anyway and I have a spare dual pump harness that I never used that I'll sell to you for cheap if you want.

 

[DSG2003Mach1]

like everyone above said...bad connection or corrosion. If you dont feel comfortable running that harness anymore, lethal just came out with "the box" and it's a (in my opinion) better version of the fore innovations controller. I was going to buy the box anyway and I have a spare dual pump harness that I never used that I'll sell to you for cheap if you want.

I'll have to look up the box, I've thought about going to a controller and maybe staging the pumps would keep the fuel system cooler vs running both pumps all the time.

Im not overly concerned about the harness so long as I dont see any rubs or anything I'll check the power and ground connections then throw the new fuse holders on and keep an eye on them.

 

[DSG2003Mach1]

like everyone above said...bad connection or corrosion. If you dont feel comfortable running that harness anymore, lethal just came out with "the box" and it's a (in my opinion) better version of the fore innovations controller. I was going to buy the box anyway and I have a spare dual pump harness that I never used that I'll sell to you for cheap if you want.

Meant to also say thanks for the offer on the harness, if I need it I’ll let ya know

 

[MG0h3]

The fore controller is nothing but a fancy looking relay.

In order to have factory prime you’d have to fire a separate relay off the correct trigger, then have that relay go to the fore controller.

Same traffic with a Hobbs switch.

I deleted that piece from my Fore order and bought 2 $7 40a relays.

Not familiar with the lethal fuse holder but maybe it’s just cheap and got cooked by the current.

All the other guys are right RE resistance causing heat….due to the extra amperage required to do the work.


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[Blkkbgt]

I agree with what others have said about loose connections causing more draw and more heat.

I would also like to add you might have gotten a shitty fuse. I've seen it a couple of times where the plastic just melts because there is something wrong with the material.

It's not super common but does happen. Cheap ass Chinese fuses.

 

[Slow 99]

Anyone have any issues running 2 pumps at all time instead of one being on a hobbs? I know its wayyyy overkill having 2 465's running all the time but has anyone had pumps burn out?

 

[MG0h3]

Anyone have any issues running 2 pumps at all time instead of one being on a hobbs? I know its wayyyy overkill having 2 465's running all the time but has anyone had pumps burn out?

Never heard any issues reported. The primary pump is running all the time so it’s not the hours that wear them out.

The heating of the fuel myth was disproven by Malcolm


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[DSG2003Mach1]

I agree with what others have said about loose connections causing more draw and more heat.

I would also like to add you might have gotten a shitty fuse. I've seen it a couple of times where the plastic just melts because there is something wrong with the material.

It's not super common but does happen. Cheap ass Chinese fuses.

It melted the holder too though

Anyone have any issues running 2 pumps at all time instead of one being on a hobbs? I know its wayyyy overkill having 2 465's running all the time but has anyone had pumps burn out?

My 340s both run full time

 

[DSG2003Mach1]

Couldn’t find anything in the wiring. The relays after the fuse holders look perfect and so does all the wiring. Wiring from holders to fuse block are good. It’s wired to the same post as the alternator wire on the engine bay fuse box, that’s right too.

I’ll undo the factory ground in the trunk being used by the circuit and double check that because why not… looks like I’ll replace the fuse holders and see what happens

 

[Slow 99]

what size fuses are you guys running for larger pumps with the lethal wiring harness? I feel like 20 amp is too small for 465's

 

[CobraSam]

Still a 20amp. Are you planning on running 465’s? What size feed/return line? Oem rails? Regulator on the stock rail where the frps was? How much power u planning? These things are really important when choosing fuel pumps. You can 1000% have too much fuel pump for a given combo.

 

[Slow 99]

Still a 20amp. Are you planning on running 465’s? What size feed/return line? Oem rails? Regulator on the stock rail where the frps was? How much power u planning? These things are really important when choosing fuel pumps. You can 1000% have too much fuel pump for a given combo.

I was planning on running 2 465's with -10 feel and -8 return with an aeromotive regulator feeding aftermarket rails. I'm planning on being around 650 to maybe 700 on e85. I think that warrants 2 465's but I could be wrong

 

[MG0h3]

I was planning on running 2 465's with -10 feel and -8 return with an aeromotive regulator feeding aftermarket rails. I'm planning on being around 650 to maybe 700 on e85. I think that warrants 2 465's but I could be wrong

Think I did my system 4yrs ago or so.

Twin 465s. 2nd pump on Hobbs.


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[MG0h3]

Man I didn’t even catch that the fuse hadn’t blown.

I’d 100% just get a better fuse setup and just monitor it with the full expectation that the holder was the issue.




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[DSG2003Mach1]

I took the grounds off and reworked those as they were slightly suspect, new fuse holders in and will keep an eye on things