Tail Light Melting

[cmsuter]

91 245. I replaced my tail light when I got the car with aftermarket and a year in, the housing that holds the bulb started melting. I replaced it with a good used OE taillight and now the same thing has happened. I'm gonna get a new taillight and make sure I clean everything up before reinstalling but what could be causing this?

P.S. I don't want to do LEDs and I don't really want to hardwire.

 

[Radtap]

Are you sure the bulbs you're putting in aren't too hot? I believe brake lights should be 21w and the smaller bulbs 8w

 

[ZVOLV]

Excessive resistance in the socket will cause heat

 

[ZVOLV]

Whenever a bulb/socket shows signs of overheating and/or premature failure, I put a new bulb holder on there and it fixes it.

Loose tension, fretting, poor crimps, poor connections all cause heat.

 

[cmsuter]

Are you sure the bulbs you're putting in aren't too hot? I believe brake lights should be 21w and the smaller bulbs 8w

The bulb in question is the taillight/brake light. Upon some investigation I found that for some reason I had a 2057 in there which is 27w as opposed to the 7528 which is 21w so that could be the culprit. I'll swap out for the proper bulb and keep an eye on it.

 

[Khrrck]

+6w still shouldn't melt the thing IMO. Make sure the contacts between bulb holder and the taillight assembly are clean and tight. If you wiggle the holder a little, the contacts should not separate or spark, but may flex a little.

 

[cmsuter]

+6w still shouldn't melt the thing IMO. Make sure the contacts between bulb holder and the taillight assembly are clean and tight. If you wiggle the holder a little, the contacts should not separate or spark, but may flex a little.

Not even over time? This taillight was installed in October 2022

 

[cmsuter]

Either way, I bought a taillight off a fellow TBer. Ifeel like the last time I did this I made sure everything was clean and tight but I'll take a bit of extra care this time and hope for the best

 

[Khrrck]

Not even over time? This taillight was installed in October 2022

It's possible, I don't have the benefit of a lot of different cars. My own melted taillights were due to vastly off spec bulbs (over double the 8w spec), but usually there is some margin of error designed into parts so that mild excursions don't damage them. Yours were only 30% over.

Unfortunately an even slightly marginal connection can get hot, pitted (from sparks), corroded, etc - and then it self-accelerates to become a very bad, extremely damaged connection quite quickly. So it's hard to tell what the initial state or cause was later. Could be that something wasn't tight, could be that the 30% was just enough to warp the plastic, loosen up the connections and zoom to a quick death.

I know you don't want to go to LED yourself, but in case anyone else comes across this thread - the power draw and heat of LED is much lower for the same light output, so you have a lot more safety margin when using them.

 

[dl242gt]

The stock bulb those were designed for is a 1073 which is slightly lower wattage than a 1157. I've had the 1157 cause melting. It just seemed to be just that bit too much wattage in my experience. I couldn't get good leds and gave up trying them and went back to using 1073 in the lights. Also aftermarket plastic isn't quite as good as the Volvo version but I've had both types melt on me.

 

[cleanflametrap]

There's only one reason the plastic melts. High resistance in a contact. Not bulb type.

If we could keep moisture out of the tail lamp housing, the contacts would not develop the corrosion that causes high resistance.

 

[Khrrck]

There's only one reason the plastic melts. High resistance in a contact. Not bulb type.

If we could keep moisture out of the tail lamp housing, the contacts would not develop the corrosion that causes high resistance.

If that's the case I'd smear a little dielectric grease on the contacts before assembly - helps keep water out.

 

[cleanflametrap]

If that's the case I'd smear a little dielectric grease on the contacts before assembly - helps keep water out.

Yes. And if that trick only lasts a month or two, the "hard wiring" will be the permanent fix.

 

[MistrThou]

If that's the case I'd smear a little dielectric grease on the contacts before assembly - helps keep water out.

Yes. And if that trick only lasts a month or two, the "hard wiring" will be the permanent fix.

I'd think in the case of the bulb holders, an electrically conductive grease would be better suited. I've only used di-electric grease on connectors with seals to help them come apart later and seal better.

 

[Khrrck]

I'd think in the case of the bulb holders, an electrically conductive grease would be better suited. I've only used di-electric grease on connectors with seals to help them come apart later and seal better.

Dielectric grease is the standard for electrical connections. It's thin enough to get displaced by the contacts when they're assembled, so it only coats the parts which aren't making the connection while still allowing the metal-to-metal contact points to work well. You might get an issue if the contacts are particularly loose and don't scrape through the grease layer, but if that's happening you have other problems.

For this application with large, decently spaced-out contacts, a conductive grease might not cause problems, but dielectric should work well and since it's an insulator, runs no risk of creating a pathway for short circuit with errant smears of grease. For example, what if a conductive grease got smeared around the bulb socket and touched both the hot and ground tabs?

 

[MistrThou]

Dielectric grease is the standard for electrical connections. It's thin enough to get displaced by the contacts when they're assembled, so it only coats the parts which aren't making the connection while still allowing the metal-to-metal contact points to work well. You might get an issue if the contacts are particularly loose and don't scrape through the grease layer, but if that's happening you have other problems.

For this application with large, decently spaced-out contacts, a conductive grease might not cause problems, but dielectric should work well and since it's an insulator, runs no risk of creating a pathway for short circuit with errant smears of grease. For example, what if a conductive grease got smeared around the bulb socket and touched both the hot and ground tabs?

I thought I had read the conductive grease was conductive because of the suspended particles, which would aid spring contacts, but the grease part was still an insulator. So it could reduce chances of high resistance in contacts but wouldn't short by its own means.

 

[Khrrck]

Well, unsure if it was the right stuff, but I've taken apart connections which had just a thin film of some kind of grease with fine copper particles (anti-seize?) which did not function at all until thoroughly cleaned. Thanks, previous owner.

Conversely I've absolutely stuffed them full of dielectric before with zero issues.

 

[MistrThou]

Well, unsure if it was the right stuff, but I've taken apart connections which had just a thin film of some kind of grease with fine copper particles (anti-seize?) which did not function at all until thoroughly cleaned. Thanks, previous owner.

Conversely I've absolutely stuffed them full of dielectric before with zero issues.

We used to have lots of issues with combination DRL/ turn singal /marker lights on the 6th Generation Chevy Malibu. they had a push in style bulb to flat spring blade connectors. They'd overheat a ton. We tried dielectric grease, but that didn't help much with the weak spring pressure. Then we switched to conductive grease just applied to the contact areas. Lots of help on those.

 

[dl242gt]

OX guard is sold at Home Depot and Lowes. it doesn't conduct but the zinc in it improves contact conduction. I put it on all the engine connections I could get to.