Please help! Headlights turn off when High beams are activated

Check fuses

The headlights are a common positive, switched ground system. You won't see voltage on the "high beam wire" when the high beams are on because it is being switched to ground. So there is nothing wrong with the readings you are getting. If I'm not mistaken you have dual-filament bulbs, probably H4. I'm willing to bet that the problem is both low beam filaments have burned out. Check the bulbs visually and with an ohmeter, and try new bulbs.

40 ohms is too much, check the ground connections. Besides, I would not use my meter to measure impedance when there is current flowing in the circuit, measure voltage or amps.

I hope you already checked the fuses before posting here.

Via email you will get the diagrams. In the mean time, in the vehicle with no DRL, the light switch controls the ground, not the positive, which comes from fuse 26 for the high beams or fuse 24 for the low beams.

Good luck

AS

Edward Hayes wrote:

The ground switching is done through the headlight switch. There are three terminals on the connector- one is the common positive that is switched on/off by the headlight switch, and will have power when the key is on and the headlights are turned on. The other two are switched grounds for the low and high beams respectively. You don't have a power problem since your high beams work, and the power is common to both. Most probably you are taking the long way around to finding out that your bulbs are blown.

Check for continuity thru the bulbs. There should be 3 pins sticking out. The bulbs I have as a spare set were the originals with my '95 LSi. They are OSRAM HB2 DOT 9003L Germany Bilux 12v 60/55w H4 37R E1 00801 w4/2. There is a flat spot on the front of the metal base. On the back there are 3 pins. The center one is horizontal and the other 2 are verticle. Ohm values are as folows: With the pins facing you , left to center is .2 ohms, right to center is .2 ohms, left to right is .2 ohms. All pins to metal base are infinite. This measurement is hard because of the low value and the resistance in the meter leads. But having continuity at least tells you that you don't have a burnt out bulb. WallyWorld has a good price on these lamps and I have heard rumors that they burn out very close to each others lifetime... If you have a 12 volt test lamp, instead of using ground and looking for power with the pin tip, hook it to positive and try to find ground...

Check out this page...

Bill

THANKS TO EVERYONE for their help and advice. With the schematic that AS sent me, I was able to find and fix the problem. I eventually discovered the highbeam ground (red) wire was damaged and corroded between the bulbs and the firewall (in the wheel well). I could never have figured it out without the schematic with its wonderful wire harness pin diagrams.

I checked the bulb elements and they were ok, but that actually was good advice. It probably is more likely to have both HB elements blow a couple of days apart, than a wiring problem.

anyway, thanks to those who gave great suggestions like "check the fuses," lol :)

Good to see you found the problem. In most cases the symptom of no low beams would in fact be from burned out bulbs. Given the age of your car, it's understandable that it actually turned out to be corroded wiring.

Glad you found it. A friend and I spent an entire day trying to figure out why he had no taillights. Bulbs were blown.