Why is my headlight fuse melting?

[doghead]

You do not connect the wires after cutting the diode out. You simply remove it and tape up the exposed wires.

 

[chesapeake]

That is the best news all day. Thank you. Now I just have to figure out how to get to it. So you have a preferred method to get to it easily. I have noticed a lot of pictures look like they were take from above

 

[bp m1009]

That is the best news all day. Thank you. Now I just have to figure out how to get to it. So you have a preferred method to get to it easily. I have noticed a lot of pictures look like they were take from above

I was able to get to it from the bottom with some little wire snips

 

[chesapeake]

Thanks. I am going to try tomorrow. Is there a way to move it away from the fuse panel

 

[bp m1009]

mine had a little bit of slack, enough that i could turn the relay and snip the wires.

 

[chesapeake]

Mine had just enough for me to turn and snip too. There wasn't enough room to tape loose ends, so I applied liquid electrical tape.

 

[bp m1009]

my next question is how do i get the horn switch out? take the wheel off?

 

[Warthog]

my next question is how do i get the horn switch out? take the wheel off?

There is no real switch. Just a tab inside the horn button that makes a ground conection.

You should be able to just remove the button. Some disassembly may be required.

 

[cpf240]

my next question is how do i get the horn switch out? take the wheel off?

Read the -20 TM?

 

[bp m1009]

Is there another relay that is the same as the horn relay, so I can swap it and try it out?

 

[Warthog]

No other relay on the truck that is the same.


GM - 25523703
NAPA - HR143 - $9
Orielly's - R636 - $8

Do we need to start a horn issue thread as this one started as a melted headlight fuse?

 

[bp m1009]

No other relay on the truck that is the same.


GM - 25523703
NAPA - HR143 - $9
Orielly's - R636 - $8

Do we need to start a horn issue thread as this one started as a melted headlight fuse?

Thanks for the part #'s and if you feel its better to start a new thread you could if you'd like, doesnt matter to me.

 

[antennaclimber]

Just for curiosity I measured the actual current draw on the main feed from the 12 volt battery that supplies power to the 12 volt side of the truck.

The ammeter was installed between the 12 volt side of the batteries and the small wire that feeds the diamond shaped terminals near the glow plug relay.

The engine was not running during measurements.

The glow plugs were disconnected at time of measurements.

The truck is not suffering from any electrical issues at time of measurements.

The truck being tested is a (mostly) stock 1984 M1009 with the resistor bypass done. I have installed new battery cables for improved reliability over the ones that were installed by previous owners.

Results:
Current draw
With nothing on --------------0 amps
Key in run position ----------3.4 amps
Parking lights only ---------4.75 amps
Headlights low beam --------9.8 amps
Headlights high beam ------13.5 amps

Heater fan on low ----------- 7 amps
Heater fan on medium ------9.4 amps
Heater fan on high --------14.8 amps

And the final one
Headlights on high beam and heater fan on high -----28.6 amps

Unfortunately I forgot to conduct a test on the wiper motor current draw. This would only add additional current draw under the final load testing.

So it is no wonder that the fuse holder is melting under high current loads.

I did order a headlight relay kit and ordered parts to build my own heater fan relay modifications. The glow plug relay will also get a dedicated wire run to it as well.
This vehicle will be test subject for future electrical modifications.

Karl

 

[firefox]

Am I missing something? Shouldn't the vehicle be designed to take that combination of loads?
I wouldn't think that combination of loads to be anything but normal operating conditions
in a cold climate at night.
Bruce

 

[Warthog]

When the wiring was new it could handle the loads. Years of dirt, grime, corrosion and wear on the system, the system is just not up to the challenge. Of course every truck is different. Maintenance goes a long way. YMMV

 

[cpf240]

Is it just me, or does it look like your 12v buss is being fed from the 24v buss? I don't see the wire that normally comes off the front battery positive to the rear battery negative dog bone cable that runs to the 12v buss block. In the picture, it appears the ammeter is connected to the 24v buss to the wire leading to the 12v buss....

Do I need to clean my glasses?

 

[antennaclimber]

Is it just me, or does it look like your 12v buss is being fed from the 24v buss? I don't see the wire that normally comes off the front battery positive to the rear battery negative dog bone cable that runs to the 12v buss block. In the picture, it appears the ammeter is connected to the 24v buss to the wire leading to the 12v buss....

Do I need to clean my glasses?

Nope, your glasses are working well. Good observation!

The bus bar was modified to have both 12v and 24v on it.
Karl

 

[Rangerpig]

Why not just do the headlight relay modification, which solves the immediate problem, and fixes and upgrades an obvious design flaw? Anybody who knows much about automotive electrical wiring will tell you that the CUCV headlight circuit is a poor design and set up for inevitable failure.
I ended up replacing my whole fuse block and doing the headlight relay modification. That not only fixed my melted headlight fuse problems, but cured a few other electrical gremlins, that up to then we had not been able to fix.

What is this headlight relay modification? I am so bad at mechanicle issues, i feel like i wouldn't be able to do it anyway.

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[Rangerpig]

If the plastic is melting that means that heat is being generated AT the fuse. That means there is a slight resistance in the contact surface of the fuse when it is plugged in. There should be close to zero Ohms of resistance across the connector when the fuse is plugged in.

THESE NUMBERS ARE EXAMPLES TO SHOW THE HEAT ACROSS A RESISTANCE. (I know they may not match the CUCV.)

Say a normal contact has .1 Ohms resistance.
P=I^2 x R = 9 Watts at say 30A when the lights are on = no problem

Say the same contact has 5 Ohms.

30Ax30A x 5 Ohms = 4,500Watts = problem

Your mileage may vary but it is because there is heat being generated at the fuse. I just watched this happen with my own two eyes 10 days ago working on wife's car. Headlight not working. Corrosion had increased the resistance of the headlight bulb connector and with the lights on I watched the wire that was showing start glowing red as it melted the connector. New bulb and cut the connector off and put two new lugs on fixed it.

What do you mean put two new lugs in?

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[cpf240]

LMC, and others, sell a headlight harness that uses relays to provide the power to the headlights directly from the battery, thus taking the load off the headlight fuse and circuit. You can also make one yourself.

What is this headlight relay modification? I am so bad at mechanicle issues, i feel like i wouldn't be able to do it anyway.

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