Parking/Tail lights fuse holder heating up

[grannyknot]

The 72 I'm working on has the usual melted fuse contact on the Parking/Tail lights circuit but as I went through the car I checked every bulb and contact points, the wires and connectors and didn't find anything concerning.  The car is back together but that same fuse holder getting hot.

Any ideas where I should start my hunt?

Thanks

 

[Zed Head]

I just linked this in the Smoke thread.  I haven't looked at it so don't know if it drops amperage through the fuse.  It might.

https://www.thezstore.com/product/5031/parking-light-upgrade-harness-70-73-240z

Beside that, have you looked at the back of the panel?  Behind that fuse?  Poor contact there could cause heat.  Looks like only one side is getting hot.

[SteveJ]

The contact that is at the point of melting is the load side of the fuse. The line side has enough copper to spread the heat out.

I know I posted in the past about the amount of current that runs through this circuit. I'll put it out there again. The design of this circuit is marginal. Using the specified bulbs, this is approximately what the current is in the circuit with incandescent bulbs at 12VDC.

The circuit is rated at 20A, so the fuse is fine, but if a previous/current owner used the wrong bulbs in the side markers (either to make the car more visible or due to ignorance), the current goes up quite a bit.

This is why I push for LED replacements. This goes double for owners of 73-76 cars as they use a smaller connector at the steering column, and I've seen that connector burned up too many times. After replacing the bulbs with LEDs, the fuse should be downrated to 10A. I can get the current down to around 3A or less on my cars with LEDs for all the marker and gauges lights.

[grannyknot]

@SteveJ Thanks, so if I change the the bulbs in the tail lights and marker lamps to LED, that should cool that side of the fuse holder sufficiently ?

Anyone have a list of LED replacements bulbs handy, I know I've seen a couple floating around?

@Zed Head I didn't know someone was making that upgrade harness, looks like that would solve my problem too.

[SteveJ]

I've never taken thermal readings, but less current flow results in less heat. I have not seen signs of overheating in the parking light circuit in my 260Z since I changed to LEDs 12 years ago.

[dutchzcarguy]

As all these contacts are rivetted i would clean up all these contacts ans solder them. (Take out the whole box) As they are 50 years old, clean them with a small rotary brush on a dremel.

Maybe replace that burned fuse contact with another one. (Out of an old fusebox) Also clean the contacts between the fuse itself and the clamps (With a soft brush, not to damage the copper, maybe use some alcohol.. no not to drink! to clean!! 😉 )  and take all fuses out and bend them to one another so the fuse is hold very tight in between..  (hope you get what i mean haha 🙂 )   Do this to all the fuses and you will have no more fusebox issues.. (Use clean fuses!)

[jfa.series1]

Don't overlook the possibility the combo light switch may be contributing to the problem. If the individual rocker and corresponding contact post are heavily carboned up that could be creating resistance that is backing up to the fuse block.

[SteveJ]

11 minutes ago, jfa.series1 said:

Don't overlook the possibility the combo light switch may be contributing to the problem. If the individual rocker and corresponding contact post are heavily carboned up that could be creating resistance that is backing up to the fuse block.

Actually if it is carboned up, it would be dropping the amount of current flowing through the fuse as it would be acting as a load in series with the lights. 

So we can solve for the nominal resistance of the bulbs, add some resistance in the circuit for the switch (0.5 ohms), and see what the circuit current would be.

So the current through that fuse would drop by over 3A. 

The switch would still be a hot spot, but it should not affect the fuse box.

[Zed Head]

5 hours ago, dutchzcarguy said:

As all these contacts are rivetted i would clean up all these contacts ans solder them.

The same assembly method was used on the ignition switch.  I had one that was so loose it would lose contact completely.  I restaked it with a punch and it came back to life.  For that amount of heat, to melt the plastic, I'd bet that it's so loose that you can see it move.

Some silver conductive paste would probably help.  But if they can be removed and soldered that would probably be the best you could get.  

Edited September 19, 2023 by Zed Head
+l

[grannyknot]

I replaced every bulb in the back half of the car with LED today, $180.00 😵, the fuse holder was too hot to touch yesterday, after the new bulbs went in it was slightly warm and consistently warm over a 5 min period, heading in the right direction.

Will replace the front bulbs tomorrow, I cleaned out my local NAPA so will have to raid the store in the next town over.

Thanks guys.

[jfa.series1]

Switching to LED bulbs will also lighten the load on the turn signal and hazard flasher cans. If you still have the OE thermal-style cans the flasher will likely not work. Switching both out to new electro-mechanical type units will take care of things. Something like this will work for both:

https://www.autozone.com/electrical-and-lighting/turn-signal-hazard-warning-flasher/p/novita-turn-signal-hazard-warning-flasher-el12/849385_0_0

I'm still running incandescent bulbs all around with relay kits, these type flashers work very well.

 

[SteveJ]

20 minutes ago, jfa.series1 said:

Switching to LED bulbs will also lighten the load on the turn signal and hazard flasher cans. If you still have the OE thermal-style cans the flasher will likely not work. Switching both out to new electro-mechanical type units will take care of things. Something like this will work for both:

https://www.autozone.com/electrical-and-lighting/turn-signal-hazard-warning-flasher/p/novita-turn-signal-hazard-warning-flasher-el12/849385_0_0

I'm still running incandescent bulbs all around with relay kits, these type flashers work very well.

 

I like this one: https://www.amazon.com/gp/product/B0811GTVH2