So I had her out for a 1,200 mile roadtrip couple weeks back, a few minor squawks presented themselves that I'll attend to this winter. Among them was that I had no instrument lights the one time we got caught out after light. Headlights work fine and I rotated the switch to each extreme position. Can not tell you about the interior lights as none of the sockets have bulbs.
The question is if the headlight switch serviceable, can one take it apart and troubleshoot it. Wanted to ask before laying out the bucks for a NOS unit assuming I can find one. Thanks.

 

YES However t;hat may not be the problem.

 

I could indeed be the rheostat in the switch, but first check ALL of your fuses. No need to replace parts if you just have a bad fuse.

 

If you find that you do need a new switch, I've had reasonable luck with off the shelf replacement headlamp switches. They seem to be a bit higher quality than some of the other miserable repop electrical parts. Rock Auto sells three brands: Standard, Rostra, and Wells. The Wells looks like it has a better rheostat than the others. I've purchased a couple Rostra parts recently, and they're pretty bad. I think I remember someone selling new USA made headlamp switches, but I don't remember what the application was, but it would be worth looking around to see what's available.

I've found that NOS switches often have as much oxidation on the internal contacts as used switches, sometimes even more, since they haven't been exercised in many decades. All NOS switches need to be checked with an ohm meter to determine if the contacts are ok. If not, the switch will need to be disassembled for cleaning.

I've rebuilt loads of switches over the years. Most times I've been successful, but every so often you come across one that's hopeless, or one that can't be taken apart without being destroyed. Many switches have one or more little springs inside that like to fly across the room as soon as you open them up. Be prepared to capture miniature flying parts. Most times a good cleaning and lubrication will get them back up to snuff. Lately I have found quite a few that have high resistance between parts that are riveted together. Carefully mashing down the rivet heads a little tighter usually fixes the problem. Check all your riveted connections with an ohm meter before assembly.

I don't have any headlamp switch restoration photos, only this overdrive switch, but it does show one of the pesky little springs that you have to watch out for.




Jeff

 

If your tail lights work, and that's important, check the third fuse from the bottom marked INST. Not brake lights, but tail lights.
If the tail lights do not work, check the second fuse from the bottom because the voltage for the third fuse comes from the second fuse from the bottom. In other words, both the second and third fuses from the bottom will kill your instrument lights, but only the second one from the bottom will kill your tail lights in addition to your inst lights.

 

Thanks guys, now I have a plan. I'll check the fuses later this morning and report back. As always....thanks.

 

It's awesome enough all the electrical questions you answer. But now you have answered mine 3 minutes before I was going to start a thread asking. Exactly as you say, no tail lights, no cluster lights, #5 fuse was blown. Like C2Dude, I will replace and report back.

Thanks!

 

Paul. If it's not the fuse there are YouTube videos on repair our vintage light switches. Be careful on those aftermarket light switches. Replaced my wiring harness and while I was at it purchased a light switch from the same vendor, I got the harness from. Drove the car for a few months before I got around to replacing the headlight switch. After replacing the switch I walked away from the car for a bit and when I returned to the garage I could smell wire's burning. Quickly pulled the battery disconnect and felt the new switch and it was VERY hot. Put my old switch back on and drove it for a while and lived with the fact that my dimmer was not functioning on the dash lights. After a while got a NOS from a respected used/NOS corvette parts guy. Didn't burn the car down but quit working in about 3 minutes. Parts guy would not make good on it as was an "electrical part". I eventually found a reproduction that works fine. Good luck. Mark

 

I confirmed that I do have tail lights. I pulled both the 2nd and 3rd fuses from the bottom and found continuity. The fuse block fuse receivers do look a bit oxidized so I cleaned them up a bit. Decided to reinstall new fuses for giggles. Headlights on and I rotated the stat. I did get instrument lights but when I rotated the **** again, they dropped off line and remained off regardless of **** rotation. Rechecked the fuses and nether had blown. So it's looking to me like the rheostat is intermittent. Look's like repair or replace unless I am missing somthing. The response regarding NOS switch functionality after sitting decades is valid and we all know their not giving those away. Marks response is more chilling. I'll take a look at the repo's out there but that seems always to be a crap shoot. What say youz?

 

This is what got me in trouble with a fellow poster on another thread concerning a headlamp issue. Some here have enough experience, a sufficiently sharp memory and a willingness to teach/help such that their advice is best followed to the letter. And if done so the problem is found and that owner's experience will stay with him as well as to be passed on to another fella. Yeah you might have plucked out all your fuses and bulbs, put them back and problem goes away, but you don't know why.

Knowing why in addition to what is a real big help when our old cars malfunction.

Dan

 

You might want to remove the switch and and inspect the contacts on both the switch and connector for corrosion. Also, use your VOM on OHMs setting to test the continuity of the rheostat. Place a probe on the rivets at each end and move the know and wire around a little and inspect for a break. I don't know the correct resistance of the rheostat, but it should never go to infinitely. Then put a probe on the movable contact and see if you get a variable reading at various points. It could just need a good cleaning and some contact cleaner.
Also look at the connector and lugs for signs of overheating like the one in the photo below. That indicates an overload or poor connection. If you have a melted connector like this one, you need more investigation to determine the cause. I don't have a diagram for your year of switch, but you can check resistance in ohms of each while pulling the switch out and following the wiring schematic.
Any high resistance indicates the connection inside the switch may need cleaned or they are broken. Most likely cleaning will fix most switches.
Not rocket science, but a little time and cleaning can do miracles.

The coiled wire is the rheostat or variable resistor.

Look for signs of overheating, melted plastic of the connector. Also clean the contacts before you do a test of each position of the switch.

Believe it or not, this switch is probably serviceable with a bit of cleaning.

 

Agree with Dan, a smoking gun and a definite answer is always better than hoping it won't come back. I'll be starting my own thread shortly.

 

Measure with a VOLTMETER on both sides of the "inst" fuse with headlight switch in the first pull detent. You should have 12v with the dimmer rotated fully counterclockwise. As you rotate the control clockwise the voltage should drop as you move and by the end read zero volts.
If you have zero volts on the left side of the "inst" fuse in all rotation spots, then move the red VOLTMETER lead to the "tail" fuse (second from bottom) and you should have 12v on both sides of the fuse (measure both fuses with headlight switch in park position and red meter lead on the CLIPS that hold the fuse and not on the metal part of the fuse itself). You can have a good fuse and get zero reading on the clips if the fuse or clips have corrosion on the surface.
Don't just look at the fuse, or measure for continuity, connect a voltmeter from a good ground with the black lead and to the fuse CLIPS with the red lead. If you'll turn on the park lights, connect the meter as I describe, and make a note of where there is or isn't battery voltage showing, I'll tell you where the problem lies. If everything was working perfectly you would have 12v on all four ends of those two fuse clips and you have the headlight switch in park (or headlights on) and dimmer rotated fully counter clockwise. Just tell me where it does not have battery voltage and I will provide a diagram showing where you problem is.
If your next post starts with "I changed", or "I replaced" instead of "I measured", I will drop out.

 

Make sure you check the metal end caps on the old glass fuses...l chased a " not start in the middle of the lake" with an old outboard for years... Finally one day when I took out the fuse for the 50 ith time, one of the metal ends fell off....
New fuse and I never had a problem with that Johnson outboard engine again...

 

Thanks Ron. So I'll get back on this today but before I pull the switch out, I'll run Jacks diagnostics.
Jack, I think I understand your instructions but to be clear, when I am checking all the voltages on the clips that you advised, the black lead is always to ground, the red to the clip. If so I should have data for you this afternoon.

 

Correct

 

Jack, With headlight marker lights on, there is no voltage on the instrument light fuse clips, either side. I checked that with the **** rotated full sweep, both directions and no voltage anywhere. There is voltage on both side fuse clips for the parking lights which were illuminated during the entire test.
What next?

 

If you're sure there is no voltage on the left side of the third fuse from the bottom, you most likely have a bad rheostat in the headlight switch. The green wire could be pulled out of the headlight switch connector or have a bad connection at that pin, but by far more likely the rheostat is not picking the voltage off the resistance coil shown in the picture. the coil could be defective, but the flat contact shown by the green arrow is probably not making clean contact with the wire coil. The first picture tells you where the contact should be made, and you will need a headlight switch to fix that.
The second picture shows you why you have no voltage on the third fuse from the bottom. The two green arrows show the connection from the rheostat to the 3rd fuse up and where it comes out of the headlight switch. The brown arrow shows where the voltage from the 2nd fuse from the bottom comes in. So, if you have it on the second fuse both sides and not on either side of the 3rd fuse from the bottom, the only choice is either the rheostat in the headlight or the green wire connection between it and the headlight switch. You can run a jumper from the right side of the 2nd fuse up to the right side of the 3rd fuse up and turn on the park lights and the dash lights will come on when you pull the switch to either position, but won't adjust the brightness when you roll the dimmer. You would just be bypassing the rheostat with the jumper and the dash lights will work normally, but always on full bright.

 

To sum up all the gobbly gook, if you bypass the dimmer rheostat and the lights work, you have a bad dimmer rheostat and need a headlight switch. but check the green wire to make sure it's fully seated in the headlight switch connector.

 

I like it Jack, clear vision on the troubleshoot. I will check the green wire as instructed but if it is properly seated, I love the idea of bypassing the stat. In all my driving life, I have never adjusted instrument lights lower. That said several members have reached out to me regarding the common reality of poorly manufactured aftermarket parts or potentially wire melting experiences with aftermarket parts. I have no interest in relocating my bed out to the garage so as to have a fire extinguisher at the ready due to a simple switch. If necessary, your bypass advice will solve my problem. YOUR DA MAN!