KSL '67 101234

Posted: April 21, 2013

I changed out all the dash panel bulbs in my '67 convertible, and as soon as I turned on the lights the instrument lights' 4 amp fuse blew. The fuse block's fuse holders were rusty, and while the wiring felt and looked okay, it is 46 years old and getting older. So, I replaced the underdash wiring harness as well as the fuse block.

The car underwent an off-the-frame restoration by a previous owner 5 years ago, but for the life of me I don't understand why the underdash wiring harness was not replaced. I thought a new harness would do the trick, but no such luck.

Okay, so the wiring is new, the bulbs are new (1816), the headlight switch is new, but the rheostat still smokes. The 4 amp fuse blows when the light intensity is turned to 100%, and the light switch's rheostat gets hot and starts to smoke. At low light intensity, the rheostat still gets hot and smokes, but not as much.

As for the new bulbs, they appear to have a stainless steel base and are listed as 1816. However, when I test them with a 9 volt battery they get much hotter than the old bulbs with a brass base, and they glow white. The old bulbs, which I don't have enough of to reinstall in every socket, have a different filament than the new bulbs and glow yellow, and stay cool to the touch.

Before I pull the instrument panel off, again, I thought I'd check if anyone has experienced the same problem. Most of the posts cite concerns about the wiring getting too hot, but nothing about the light switch's rheostat smoking.

Update: April 27, 2013

Problem fixed, or so I thought!
The fix was replacing the "new" bulbs that I purchased online from a major Corvette parts house that burned as hot as a torch. I have no idea what the problem is with the "new" bulbs, and at this point I don't care. My advice for anyone replacing burned out bulbs is to buy GE or Sylvania 1816 LL bulbs for the dash panel, radio, and clock from local stores. What a relief to see light with no smoke.

I wasted a month of weekends chasing a problem that should never have been a problem because I relied on a Corvette parts dealer to sell quality parts. Lesson learned! On a positive note trying to solve this problem led me to replace the 46-year old wiring harness as well as other electrical components.

Update: April 27, 2013 (later in the evening after celebrating)

I posted earlier this evening that the smoking rheostat problem was fixed. I was premature in my conclusion. I wanted to see in my darkened garage how the dash panel looked with the new bulbs glowing so I pulled the **** out to the running light position and watched for any signs of smoking as I ran the switch through the dimmer range.

The problem is not resolved - the rheostat smoked and heated up when I dimmed the dash panel lights. However, I am on the right track in diagnosing the problem because the rheostat stays cool and does not smoke when the dash panel lights at are 100% i.e. **** turned all the way counter clockwise, or when the lights are off i.e., the **** is turned all the way clockwise. The newly purchased Sylvania bulbs (1816) are rated at 4 watts (I could not find 3W bulbs), or 1 watt greater than the original specification.

While I appreciate the info and advice on changing to LEDs, before I introduce another variable like switching to LEDs, I want to fix this problem and know that I'm not risking a dash fire. I want to drive this car with complete confidence of its reliability and safety.

So while changing the bulbs to 1816s helped it did not resolve the heat build-up that is causing the switch to smoke at the rheostat. And yes, the switch is a non-NOS switch. I will start searching for a NOS today as well as for 3-watt bulbs.

As I mentioned I think I am on the right track in that I think too much current is passing through the switch i.e., 15 bulbs @ 4 watts or 60 watts, and the system was designed for 45 watts i.e., 15 3W bulbs (see 1967 Corvette Assembly Manual Section 12, page D3) The fuse should handle a load of 48 +/- watts coming from ~12v @ 4 amps or 48 watts.

To further troubleshoot today I am going remove the bulbs in the clock, as they are the easiest to access, as well as a couple in the dash panel and see if reducing the total bulb wattage to under 48 watts has any effect on the rheostat's temperature and smoking. I'll provide an update later today for those of you following this saga.

4/28/2013 12:30 update

I disconnected the clock lights and found no change in the heat buildup of the rheostat. I have 3 light switches and found that they all heat up around the ceramic block the same when the panel lights are dimmed, but don't when set at full light intensity. I took one apart and it looks like the lubricant used on the sliding mechanism inside the light switch melted and came in contact with the hot spring leading to the smoke at the rheostat.

How hot is the ceramic housing around the spring supposed to reach? I replaced the headlights to halogens last fall to increase the headlights' light intensity (I went back to the original T3) and remember the light switch heating up as well. The high-beams fluttered and I traced that back to the switch as well - hence the first new switch. That is the first time I recall the light switch being hot. Shortly thereafter, I pulled the dash panel to get access to the panel lights and a loose instrument panel ground wire and found that 6 panel lights were burned out - so 6 lights or 18 watts of power was not flowing.

So am I chasing smoke in the wind? Is the switch's ceramic block supposed to heat up so that it is too hot to hold between fingers, as is my situation? Or, hot to the touch but not uncomfortably hot? Or, warm to the touch, and able to be held between fingers for an extended period of time?

April 29, 2013:

The problem seems to be solved. I took the car out for a drive with the lights on, and the dimmer **** turn to the brightest intensity. The panel lights stayed lit, the 4-amp fuse did not blow, the dash lights have a beautiful glow, and best of all the light switch did not get hot and smoke. So what was the solution? Turn the light switch control **** counter clockwise to the brightest setting and don't dim the panel lights. The ceramic heat sink is trying to do its job by absorbing the heat generated when the panel lights are dimmed. But its design won't allow it to do so sufficiently and without creating a risk of a fire. I found that out by reviewing other posts that describe issues associated with heat buildup when the dash lights are dimmed. It seems a safe, sensible solution is to bypass the dimmer function i.e., make it non-functional, which is described at the end of this post.

mike coletta

Are the bulbs "marked" 1816?? Sounds like you don't have the correct bulb. The 1816 bulb draws about .33 amps at 100% (13V). If the bulbs are getting hot, and stuff is smoking, I would say that you have something less than a 13V bulb.......Maybe a 6v.

Mike Coletta

62Jeff

Assuming you put the correct bulbs in the car......then does your car have factory A/C?

If so, check out my nightmare
http://forums.corvetteforum.com/c1-a...ort-still.html

With new wiring and new bulbs in my factory A/C 65, I was pulling over 5 Amps on the 4 Amp circuit. A second new dash harness confirmed the same problem. Exhaustive testing pointed to the bulbs, so I replaced nine 1816 bulbs with 1895 lower rated bulbs and a 5 amp fuse.

Frankie the Fink

LED time:
http://www.superbrightleds.com/cat/l...r,BA9S,21,198:

Plasticman

Frank,

Have you changed to LEDs? Which ones did you use, and how do they work (brightness / even illumination / proper function of rheostat / color)?

John (plasticman)

Scott Marzahl

I just had something similar occur when I was installing new LED bulbs and comparing them to the new silver based 1816 bulbs made in China that came with my new harnesses. I had LEDs rated at 31ma in most positions and was going to compare brightness in the radio with the 1816 bulb provided by Lectric Limited, but whenever I installed the 1816 bulb the fuse would blow. Installed the LED bulb and no problem. I did not measure current through the bulb, but that would be interesting to see if these bulbs are being manufactured incorrectly. With LEDs installed in all positions there is no problem with the 4 amp fuse.

Frankie the Fink

John - I have not gone over to the dark (light ?) side yet for dash bulb LED's but some other C2 owners on here have. I DO have them for parking, brake/tail and license plate lights however in the '61 and have used an LED light 'strip' in my Chevelle clock to replace the cr@ppy, light bulbs that the repro console clock initially had...

However, the LEDs draw a fraction of what a bulb does so it looks like a possible solution to the OPs "over-current" problem with the new edition of 1816 bulbs - something doesn't seem right with them

toddalin

This reostat problem has been my concern, that I've expressed a few times.

Frankie the Fink

For whatever reason - when you see smoke from an electrical component; it's more often than not heat from too much current coming through it. You either beef up the component or try to reduce current. In this case it seems like the modern bulbs are over-taxing the circuit. One way to deal with that is to replace those bulbs with other equivalent items that draw less current. Some of the LEDS draw only 30 milliamps...or about 1/10th of what the bulbs draw.

Having said that you would have to confirm that that the LEDs give satisfactory illumination for the various settings of the rheostat.

Scott Marzahl

Further to where Mike was going, verify the voltage output from your rheostat going to the bulbs. If its a lot less than 12 volts with a fully charged battery when turned up it could be faulty.

TheGanzman

This (timely!) thread was all *I* needed to "change horses" from the larger bulbs that I had ALREADY bought & installed (along w/the 10 amp fuse) but not buttoned the dash up yet, to a large $ order for LED's - anybody wanna buy some #1416's & #1816's? Like French Freedom Fighter rifles - NEVER fired, dropped once...

wmf62

what LEDs did you use?
Bill

TCracingCA

Without burning your car to the ground with an electrical fire. I would see if you have an excessive voltage drop on your system when you energize the dash lights, thus pull the fuses on the other systems. Also as a minimum I would change the switch!!!!!!!!!!!! Now that you have maybe proper load being pulled, the switch is old and might not be capable of handling it. Also you have grounds and could have a short that has cause it to smoke the component, direct current to ground (causes smoke) but that if they were still lit could be intermittent. Even if they were foreign pieces of crap (inferior bulbs), I doubt that the amperage pull would be so excessively wrong that you would develop the symptoms described. Oh ya!, keep your fire extinguisher handy!!!!!!!!!!!!!!!

Frankie the Fink

The wiring, switch (with the internal rheostat), and, bulbs are all new let's not forget...as stated in the initial post.

TCracingCA

You check further and because it """""smoked (burnt), sizzled"""---- after you troubleshoot further--- YOU CHANGE IT AGAIN!

Frankie the Fink

One of us should certainly think about what he says.
A newly installed component with potential damage is not an "old" component.

mike coletta

I went back and read the OP, and he says that it's smoking "most" when the lights are at high, so the rheostat doesn't even come into play, as it is a direct button/slider connection on the switch. If there was "smoke" in this position, it's not coming from the rheostat, so it must be wire burning (not a good thing). I'm still saying that there is either something wired wrong (like a short to ground on the hot side of the bulbs), a pinched wire (hot side of one of the bulbs), or the bulbs are wrong (too much current draw).

My money is now on a pinched wire, AND you might also now check all of your wiring, as something has probably melted, which was what was causing the smoke. Since the smoke was less on low intensity, and assuming that the rheostat was dropping the voltage, the shorted wire wasn't getting as much juice, and therefore smoking less!!! Just a thought.

Mike Coletta

TCracingCA

The OP can monitor the replies and comments to see if they correlate to the symptoms that he shared.
So to everyone of the proof readers on this forum, Sorry I missed that it was also a new switch. But since it burned-- "it is old now!" Throw it out. Troubleshoot the system more.

The next guy came along with a good direction with shared knowledge about the Rheostat, instead of proof reading everyone else and the preciseness of their reading. He contributed!
Also I will bet that when he pulls the switch out, some of the burned wiring will be present where the smoke came from (and the proof readers, please check my reading ability further if necessary), but I think he said the smoke was from the switch!

GreaseMonkey

I had that problem. Pulled the damn switch and put another new one in. Too much invested to have it melt due to a faulty switch

TheGanzman

Agreed! And "nut up" for an NOS Delco Remy - not cheap at ~$120+ on FleaBay - but not made in Chine-Wa neither...