nola442

I recently changed my outer low beam T3 headlights on my 1970 Cutlass convertible to Sylvania Xtravision halogens (part #H5006) and now my high beams will not turn off. At first I thought I had a dimmer switch problem, so since dimmer switches are cheap I changed that out, but the high beams still did not turn off. Then I jumper wired the dimmer switch connector from blue wire to tan (low beams) the high beams still did not turn off. Has anyone ever had this sort of problem with Sylvania Xtravision halogens?

Oh, I even switched the Sylvania low beams around (driver to passenger and passenger to driver) and the problem persisted. Eventually I found a old low beam headlight, installed it on the driver side, and things started working again.

I'm totally scratching my head on this one. I can understand one faulty bulb, but two?

MDchanic

Sounds like the pinout on the new bulbs is different from one of the old bulbs.

- Eric

oldcutlass

x2

GAOldsman

x3

joe_padavano

X4. I'll bet that one of them is made wrong. Try changing out one, then the other, and see which one is wired wrong. Of course, if they're from the same lot, it could be both.

droldsmorland

Call Sylvania's Tech line with a copy of your cars head light circuit schematic in hand.
They may offer a modified harness or you may have to swap the terminals in the plastic housing. But that wouldn't make sense because that bulb is most likely made for this application. They may also tell you to run the lights through a slave ice-cube relay. While that's not a bad idea Id think these bulbs should be plug-n-play? Could be a bad batch of bulbs?
Grounds, Grounds, Grounds....clean all 40+ year old grounds. Your ground circuit could be bad to where it works with the old school bulbs but not with the higher draw halos. Try cleaning the forward core harness grounds. There is one above each light bank. Also make sure the terminals in the plastic connector are ok and making good contact with the bulb terminal
Lets us know what the fix was because you're probably not the first or last to have this issue.

Joe you type too fast I concur possible bad batch...look where they're made!

joe_padavano

The system works correctly when he puts the old headlights back in. This is NOT a ground issue or any problem with the car's wiring. This is a problem with the new lights.

droldsmorland

Right, Right agreed for the most part, possibly a bad batch but a rare occurrence for sure.... or an incompatibility ....you type faster then I. Splitting the dictionary doesn't quite apply here because of the new style bulbs. He did an apples to oranges check. Others have encountered this same issue on older and newer vehicles with the various types of new and improved non OEM bulbs available today. Some manufactures go as far as requiring a modified harness upgrade...off subject. Many have encountered switched ground incompatibilities or just plain old bad grounds. People are needlessly replacing parts when most of the problem was linked to some type of grounding issue.
And you have to admit bad grounds are often the cause of many gremlins in the older negative ground systems. I kind of put that in as a disclaimer when discussing electrical on the older cars. It cant hurt though may not, as you mentioned, be the root cause.
Certainly will be interesting to see what the fix is?
I'll bet the tech line will hold the answer.
I tried to copy the headlight diagram from Wild About Cars dot com but it doesn't copy well.
nola442 check it out if you don't have a handy diagram. All the manuals are there. The manuals are available on line in hard copy.

nola442

Thanks everyone for the replies.

I agree. I don't think it's a problem with the system since the repro-T3 lights work. After reading everyone's replies I think it's a wiring issue in the bulbs. I'm going to try to contact the manufacturer and see what they say. Also, I bought each bulb at a different store here in Louisiana (AutoZone and PepBoys), so if this is a "bad batch" issue, then it's going to be pretty prevalent. I'm surprised that no one else has come across this issue because I think that wiring setup is very common on late-60s and early 70s cars.

Finally, if the manufacturer can't assist, then I'll try jumper wires on the bulb connectors and play around with the connection combinations to the wiring harness connector to see what works.

Here's another thing. Like I said in my original post I left one of the new halogens in the passenger side position, then installed the old T3 in the driver side position, and things worked. I'm guessing that even an incompatibly wired bulb would work on the passenger side since it's at the end of the circuit. Just a novice guess.

m371961

I would guess the drivers side lamp is faulty. The low beam circuit feeds both low and high filaments in this new lamp, the current then flows back through the harness and feeds the other side.
You can test this theory with a continuity test.

joe_padavano

It could be either side. The harness is spliced in the connector that goes to the driver's side, but electrically, that is irrelevant. Either side could be bad and cause this problem. You can test this very quickly by unplugging one low beam and testing to see if the other side works, then reverse. The headlight circuit is pretty simple. Just look at the wiring diagram in the CSM.

m371961

The only reason I suggested the drivers side is that is the one he said he replaced with the old one.

RandyS

I'm a bit confused by your post. Are you saying that there is a 'common' conductor on Halogen bulbs? That is common to most all headlight bulbs. If you feed power to both filaments, would they both not be on? How do they control them?

m371961

I'm sorry I am not explaining this well. Headlamps have 3 terminals. One for ground, one low, one high. If the new lamp is faulty, in can internally connect the low and the high together. Then the other side would also only stay on high as the harness would feed the high side.
If you replaced the drivers side new lamp with the old lamp and it worked correctly, Replace the new lamp on the pass. side with the new lamp you removed from the drivers side. If the problem comes back, that lamp is bad.
It can be checked with a meter on the lamp with it unplugged, but I don't know how to explain it.

RandyS

O.K., I follow you now. I thought you were saying that with Halogens, you feed both filaments at the same time - couldn't figure out how that could work.
I think if the OP would use a DMM and check for a short between the low and high beam pins on the lamp itself, it would prove your theory. If no shorts are found, I would suspect the problem is with the pinout on the new lights, as Joe mentioned.

MDchanic

There is no practical way to do this.

Incandescent filaments have essentially zero resistance when off, which builds to their rated resistance in about ¼ second once current passing through them heats them up. If you check it with an ohm meter, all of the connections will look like dead shorts.

- Eric

RandyS

There will be 'some' resistance to a filament, more than a dead short.

MDchanic

Yes, but will it be measurable?

- Eric

TripDeuces

Did the ground wire on the radiator support come loose or break?

m371961

A meter should show an open circuit between the low beam and high beam posts on the lamp, right?

joe_padavano

No. It will show the resistance of the low and high beam filaments in series. They are connected together on the ground side. The wiring of a dual filament bulb is like a "T". The bottom leg of the "T" is the ground, one side is the low beam and one side is the high beam. Connect a VOM across the low and high terminals and you are just measuring across the top of the "T".

Note that given a VOM that is sensitive enough (and the free ones from Harbor Freight are NOT), you should see higher resistance measuring from low to high terminals than from each of those to ground.

m371961

Thanks Joe, I can be dense and hardheaded but I now understand how the loss of ground on one side affects both.