headlight issue
 

I recently purchased a '93 300 non-turbo, and did not check the headlights before purchasing it. The other night, I switched the lights on and to my surprise, no headlights or fog lights. Tail and side markers work. I pulled the 4 headlight bulbs and they look good, but bought one to see if bulbs still might be the problem. New bulb doesn't work either. I have 12 volts at the socket of each bulb which is confusing to me. Good bulbs, 12volts and I would think I would get light, I am missing something pretty basic here. Can someone enlighten me? I would prefer not to take it to a mechanic for trouble shooting. That could get real expensive, fast.

Welcome to the forums.

When you check the socket, are you checking inside the socket or at the wire leading up to the socket?

Also look closely inside the socket for dirt, crud, damage, corrosion, etc. It's possible the bulb isn't seating properly. That or there's some loose connection between wiring and socket.

Also make sure it's grounded.

Thanks for the reply. I removed the 4 headlight bulbs, the fogs are a bit more difficult to get to so I left them in, and iI checked for volts by probing the inside of the socket and grounding to the motor. I read 12v on all sockets. I took my switch apart (completely) and cleaned all contacts with denatured alcohol. I didn't check the diodes because I didn't know what the reading was supposed to be. Cleaning didn't improve anything. When I probed the switch with my test light, I had power in #5,6 &7 in both #1 & #2 switch positions. I had no power in #1-4 in the #2 (full headlight position). So, having done all of that, I'm thinking bad switch. Any thoughts?

Well, I wouldn't think there'd be a reason to check the switch if you are measuring power at the bulb sockets. The switch is what sends power to the sockets and it's accomplishing that if you are measuring power there I think.

A couple more questions:
Did everything look clean inside the socket?
Is the socket grounded? You said you grounded your test meter to the motor but did you try grounding your test meter to the socket itself?
Do you have the right bulb? When you bought a new bulb, did you simply match the old one like most people do? or did you look up the correct bulb for use on the car?

Sockets looked clean but I will make sure by cleaning them. Good point on the grounding location, I'll re-check that. The switch isn't registering any output through the 1, 2, 3 or 4 connectors. According to the FSM, I should have power in 1-7 when the switch is turned to #2 or headlight position. I just figured that was a problem. ?.
Thanks for your time on this, it really helps to have someone to talk to when troubleshooting.
Regards, Whit R

I'm having trouble downloading your FSM to look at the schematic. In the mean time, if you found power at the socket with your meter, then the issue of your headlights not working is between the bulb and the socket. Either the bulbs are bad, you have the wrong bulbs, the bulb isn't seating properly (ie wrong bulb or something is blocking it from seating all the way down) or the socket isn't grounded properly.

Now, if you weren't reading power at the socket, then I would say lets look at the switch. Anyways, as soon as the download link for the FSM on your car works for me, I'll take a look at the schematic.

Thanks a million. I really appreciate your efforts on this.
Whit R

Pulled the bulbs out again, inspected, cleaned them and the sockets with CRC DQ. Noticed that the fog lights came on when the headlight bulbs were pulled out, but the fogs would not work when I put the bulbs back in. When checking the sockets for power, using the opposite connector for ground, I got mixed results. I must have a defective socket or a bad ground. The bad ground puzzles me because the running lights work and the fogs worked w/o hdlt bulbs in their sockets.

I'm not familiar with the 300's. I have a 280ZX. So, what does the fog lights have to do with headlights? I also don't understand what running lights are. Are they all the same light coming from the same bulb in the same socket?

Fogs are on the same switch panel as heads and use the same ground. Running lights are the side markers, front and back; I probably shouldn't call those running. I think you are correct about it being a ground problem, I just haven't found where it isn't making contact. Thanks for your help,
Whit

So the fogs, heads, and running lights are three different lights from three different bulbs and three different sockets then.

Fogs came on when headlight bulb was pulled out but fogs turn back off and don't work when the headlight bulb is in.

Very weird. Is the fog lights fully operational without error with the headlight bulb out? If so, then I'd say there's something going on with the headlight socket. If they aren't too expensive and easy to find then I would just replace that but it almost sounds as if the bad ground is caused by the bulb being put in. You might try completely removing the socket and inspecting it closely, inspect the wiring closely, inspecting the ground closely, etc. I'm chasing some odd ball wiring issues myself

If you're getting power from the socket by grounding to the chassis, try putting the bulb in and grounding the back of the socket to the chassis, see if it lights.

I was having headlight trouble recently due to corrosion. I just R^2 all the canon plugs.

Thanks guys for the input. I'll try the grounding idea tomorrow. I'm not ready to replace the sockets yet, though that may be the only remedy.
Whit R

How do you do that? I don't see anywhere on the back of the socket to ground.
Whit R

You can:

• Make a wire lead, put it in the canon plug, then plug the bulb in on top of it
• Get a sharp probe and stab it into the back of the plug where the wire goes in
• Use a wire crimp to jump off the line right behind the plug

Thanks, I'll give it a try.