hot headlight fuse holder

[Landpimp]

on my stock 64 fj45LV. WHen the headlights(sealed beams in this case) are on the headlight fuse holder gets REAL hot.......like enough to leave a mark on my finger. My 66 fj45 did the same thing with H4 installed, I "cured" this by upgrading the headlight harness on it. But I don't really want to do this on the 64 as it involves hacking a hole in the back of the headlight buckets. I actaully have a harness I bought for it, but somehow I must have got the wrong one, it has plugs for 4 headlights.......had it so long I lost the package.

But regardless, why is the holder geting so hot? don't seem right.....almost downright dangerous. I have cleaned the fuse holders, checked wiring ect.

Thoughts?

 

[IDave]

Heat = high resistance, somewhere in the circuit.

When that happened to me, it was corrosion in the plug to the headlight switch. Melted the plastic on the corner of the fuse box cover, burned my finger. Also, melted the plug (which in retrospect was a big hint.) Like what you are seeing, John. I ended up getting a multimeter and tracking down the problem that way.

 

[Landpimp]

what the trick to useing a multi meter to track down high resistance?

Heat = high resistance, somewhere in the circuit.

When that happened to me, it was corrosion in the plug to the headlight switch. Melted the plastic on the corner of the fuse box cover, burned my finger. Also, melted the plug (which in retrospect was a big hint.) Like what you are seeing, John. I ended up getting a multimeter and tracking down the problem that way.

 

[IDave]

Ha! I am an electrical bonehead. I had to be walked through it, but IIRC, it involves setting it on OHMs and testing segments until the resistance jumps way out of range. Davee and Poser (and a number of others) gave me lots of help.

Here's a link to that discussion: https://forum.ih8mud.com/showthread.php?t=16071

 

[Landpimp]

I will do some reading. I have never been able to figure out the ohmes/resistance settings, but I suppose its time

Ha! I am an electrical bonehead. I had to be walked through it, but IIRC, it involves setting it on OHMs and testing segments until the resistance jumps way out of range. Davee and Poser (and a number of others) gave me lots of help.

Here's a link to that discussion: https://forum.ih8mud.com/showthread.php?t=16071

 

[drohweder]

I will do some reading. I have never been able to figure out the ohmes/resistance settings, but I suppose its time

I'm getting ready to pull my entire harness (like you rec pimp) and lay it out and run the whole thing. Time for me to learn how to use the multi meter as well. I got the voltage down

 

[72cruiser]

have fun with all that fellas...did a little bit myself this weekend

yeah, the heat is a by-product of resistance...my whole fusebox got nasty hot when i was workin on my headlights. (rust on the back of the connectors in the fusebox)


malphrus

 

[Rocky_LC]

I agree with JM - The heat will be generated at the place where the high resistance is.... So... It's in the fuze box. I would check the contacts clamping in the fuze (a round file can buzz off the rust) - that's where my problem was, or the back of the connectors (like he said). Make sure the battery is disconnected when you start poking into the electrics with a metal file...

Rocky

 

[72cruiser]

also,
i have a good fusebox (with 8 fuses) that i just took off my 72 fj40
if you need one with clean connectors on the back...let me know, and i can get it out to you in about a week (it's at my house at school)


malphrus

 

[72cruiser]

Make sure the battery is disconnected
Rocky

i second this suggestion...really big sparks, ha ha


malphrus

 

[dd113]

The heat is resistance but you should expect the headlight fuse to get hot as it take a lot of current to run. Chances are it is the plug from the harness to the light. The only real way to fix is to replace.IIRC early trucks had an insulator block on the lower fender that splits to both sides for the running/turn/head lights. I would start there for a resistance issue.

 

[spotcruiser]

John,
If the fuse block gets hot when only the headlight circuit is energized, it's because:

1. The circuit is drawing more current than it was designed for (aftermarket headlights of a higher wattage than stock).

and/or

2. There is a high resistance connection at the fuse block. Don't know about early fuse blocks, but later FJ40 fuse blocks have riveted connections on the back for each fuse. The rivets get loose/corroded, which results in higher resistance and heating at that spot.

Your problem may be one of these or a combination. I'd pull the fuse block and clean/tighten the connections on the back. The problem may also be due to poor connection at the fuse, so clean the fuse clips as well.

By the way, disconnect the battery before you start pulling apart the fuseblock.

Good Luck.
Todd Bull.

 

[Yoda]

John,

2. There is a high resistance connection at the fuse block. Don't know about early fuse blocks, but later FJ40 fuse blocks have riveted connections on the back for each fuse. The rivets get loose/corroded, which results in higher resistance and heating at that spot.

.

That is what I had wrong with mine. Headlights draw more current, so any resistance makes heat. I pulled my fuse panel, glass bead blasted it, and soldered all of the rivet spots to give good connections. Has worked good for years now.

Mine had gotten so hot it melted the solder out of the fuse and the lights ALL went out!

 

[toddslater]

When mine did this, turned out to be some funky cross fed wiring debacle done by a PO. Somebody put in some splice clips thingies just aft of the headlight harness plugs just after it exited the fuse block..spliced a couple wires onto each other....makes ones head spin. None the less, I removed said abortion and it solved my problem. Your problem is probably what others have stated above, as your stock lv appears to be very unmolested. But then again...so did my 40...so it's a least worth a mention and a peak at the wiring exiting the block going to switch and lights.

 

[IDave]

I will reiterate what David Dearborn said, because it is clear that some of you don't agree. And while I don't claim electrical expertise, I can truely say I "proved" this point in my circumstance using my OHMmeter. And that is this:

If you have a high resistance point ANYwhere in the circuit, it will mean that the current flow across the fuse is increased (to overcome the resistance), and that will heat (and eventually melt) the fuse.

Although it CAN be, the high resistance point is NOT necessarily at the fusebox. It is likely to be at a (any) contact point that can corrode, or it might be at a short, such as Todd is describing.

 

[Steve C]

One way to troubleshoot this type of thing is:

1. Get a volt meter. get some wire and somehow extend the length of the ground side probe of the voltage meter to about 20'.
2. Attach the end of the 20' ground lead right to the (clean) batt - terminal.

3. Now, set the volt meter to a range a little higher than 12 volts. at this point you can walk around the car with the volt meter and take readings of voltage without getting faked out with potential ground problems.

4. here's the fun part. measure the voltage at the + terminal of the battery. This is the max reading you will see anywhere on the car (with the engine off)

5. Trace through the circuit, starting at the battery + (nom. 12 volts) and working to the batt - terminal (0 volts), measuring volages as you go. For example, say you take a series or readings of 12.5, 12.3, 12.2, 11.5, 11.4 volts. The place where you see the big drop of voltage is where the problem is (it will also be the hot spot).

No need for ohms. it only offers the opportunity to fake you out.

 

[honk]

"No need for ohms. it only offers the opportunity to fake you out" ...but it's ohms that make for voltage drops.


All headlights draw high levels of current. Old wire and connections have higher than design level impedance because of oxidization. Adding higher than original output lights to old circuits amplifies the problem. This shouldn't surprise anyone.
Probably the best and easiest fix is to run them on direct battery connections through heavier than stock wires and a relay. To put it simply you connect the headlights to the output terminals of a relay with 12 gauge (or bigger) wire. The relay can be mounted close to the lights. Then lighter wire, the stock 16 gauge(?), and the original dash switch can be used to energize the relay and turn on the lights. A relay is a secondary switch and you'll hear a click when you switch on the lights. The circuit should still be fused of course but by doing this you'll end possible smokeouts of even fires.

All I'm describing here is exactly the wiring usually provided in good aftermarket light wiring kits, so most of us have the needed parts leftover from when we decided that all that crap wasn't necessary to make the lights work.

 

[Landpimp]

WOW guys lots of great info

yes the fuse got so hot that it melted the solder.

only is the headlight fuse. Healights are stock sealed beams. Wiring is all stock.

I "cured" this same problem on the other 45 by upgrading the headlight harness, not wanting to so this on this 45

so time to get the meter out and start cleaning some stuff up. I have some questions but I gotta read all the replies again when I am more awake.

thanks

 

[mallred]

"No need for ohms. it only offers the opportunity to fake you out" ...but it's ohms that make for voltage drops.


All headlights draw high levels of current. Old wire and connections have higher than design level impedance because of oxidization. Adding higher than original output lights to old circuits amplifies the problem. This shouldn't surprise anyone.
Probably the best and easiest fix is to run them on direct battery connections through heavier than stock wires and a relay. To put it simply you connect the headlights to the output terminals of a relay with 12 gauge (or bigger) wire. The relay can be mounted close to the lights. Then lighter wire, the stock 16 gauge(?), and the original dash switch can be used to energize the relay and turn on the lights. A relay is a secondary switch and you'll hear a click when you switch on the lights. The circuit should still be fused of course but by doing this you'll end possible smokeouts of even fires.

All I'm describing here is exactly the wiring usually provided in good aftermarket light wiring kits, so most of us have the needed parts leftover from when we decided that all that crap wasn't necessary to make the lights work.

Excellent solution, I have been avoiding driving at night since I will periodcly loose the head lights due to the fuse blowing and been putting off the cleaning of the fuse block.

We do the relay system on the boat a lot when we have long runs 200' +.

I think I will put a fuse or circut braker on each headlight so you don't loose both at the same time as I do now.


I don't think Pimp will go this way with the StricklyStock 45, but it is a good improvement IMO.

 

[Steve C]

"No need for ohms. it only offers the opportunity to fake you out" ...but it's ohms that make for voltage drops.

The problem with trying to "ohm out" a lighting circuit is that it ignores a few things:

1. It makes an assumption of linearity for a circuit, where it is the case that most are non-linear. To get in and try to "ohm out" a liting circuit ingnores the fact that the bulb is non-linear, and dosn't have a fixed resistance ("ohm") value. (as the filament heats the current goes down)
2. It assumes an intuative knowledge of electronics. While most people would have trouble analyzing a electrical network of the scale of a car, almost everyone can understand the concept of following a voltage "down hill" to ground. This equates to kirkoff's law in electrical engineering.
3. It's really hard to troubleshoot ground loops unless the circuit is powered.

All just my opinions. (based on having tried to do things the hard way)