Had a couple small items to fiddle with on my 70-442 today. As soon as I got in the car I noticed a black/burned like spot on the right side of the rearview mirror. That entire area where the light area is located was red hot and left a black spot on the mirror itself. I have my battery connected to a trickle charger, but not disconnected at the positive terminal to the car. Can I assume that is a no no and that is why that mirror light melted? If that was not the cause, what would cause a melt down like that? Possibly I accidentally hit the switch into the "on" position and that was the cause (I don't think I did, btw)

 

I'm not gonna pretend I know the answer to your question, but I will say that you need a battery disconnect in place on your car. Any toy connected to a 12v battery around my house has a battery disconnect installed.

 

I don't think the trickle charger would do that, they push small amperage. When the lamp is on it draws a set amount of current based on the resistance in it's circuit which is probably the lamp the wiring and the switch. My money would be on a switch left on inadvertently, those incandescent bulbs can draw enough constant current to heat up quite a bit, and with the battery on a trickle charger your battery didn't loose any energy or at least that much energy. If you don't think you left the switch on then there may be a another reason that circuit got 12 volts to it, maybe the switch is shorted to 12 volts. I bet someone has the service manual for your car and could verify what I speculated and I may be wrong but am basing this on my general knowledge in electronics and how most cars are wired.

 

I agree, this was not the fault of the trickle charger and most likely that the switch was left on and overheated the lamp, socket, and lense.

 

Another agreement that the switch was turned on inadvertently. I did that back in 1990 while cleaning the car and didn’t realize until the next morning when I got in the car to go to work. The mirror was cracked and when I touched the glass it burned my finger it was so hot. That mirror map light isn’t visible in the daytime so it’s hard to tell if it’s on or off.

 

If your rearview mirror is original to your car try to save it. Give Scott Winn (oldspackrat) a holler. He repaired mine.

 

Every one of those map lights I've seen have had discolored spots from the bulb overheating. Unfortunately I think it was just a poor design. You may want to consider an LED replacement bulb that will draw less current and run cooler.

 

You said it Joe, that's the solution right there. That was swimming around in the back of my mind to recommend that but somehow the thought drowned, or got caught on a piece of ethereal flotsam or something. Those LED replacements are nice but in some occasions may be too bright. Kind of like having a custom Foose steering wheel in an otherwise bone stock original 40's era fat fendered rocket, just don't fit right.

 

I replaced all the interior lamps with LED bulbs for exactly the reason mentioned. I replaced all the lenses, I didn’t want them to discolor again. I don’t think the LEDs are too bright, but they do have a different color compared to standard bulbs.

 

Discolored/melted lens' can be caused buying the wrong bulb. The bulb may look the same and physically fit the socket but it is the wrong (higher) wattage. The higher heat can damage the socket and lens.

 

Thx for the responses everyone. I will repair it later today