Trouble with tail lights and rear sidemarkers

[wkilleffer]

Hello,
I noticed the other night that, while my headlights were on, my tail lights were not. However, the brake lights and turn signals were working. The left turn signal was a bit slow, but that's not been unusual.

I tore into it today looking for an obvious answer. I checked the bulbs by switching in new ones, but there was no change. I checked the nuts that held the lights onto the body, and they were a bit loose. I cleaned the grounding areas and refastened everything, but they didn't work. I went on to the rear sidemarkers and did the same thing, but there was no change. I then noticed a loose wire on the right tail light and fixed it, but there was no change. I also cleaned the ground points around the rear sidemarkers again.

This also lead to me cleaning that large grounding place behind the license plate bracket. It needed it, and now the car seems to run better, but the tail lights still don't work.

This has happened before, and I can't remember what I did to cure it. The rear harness isn't but about three years old. I'm thinking this could be an under the hood problem. Any answers as to why my brake lights and turn signals would work, but not the tail lights, nor the sidemarkers, nor the license plate lights would be most appreciated.

Thank you,

 

[wrenchpuller]

Hi William,
I think I would start looking at the connections at fuse-box and the cluster of bullet connectors rhf side by bulkhead/fender
Cheers Ric

 

[PAUL161]

Hello William, I was going to say the same thing as Ric. Start at the fuse box and work back down the harness. There is definitely a bad connection somewhere. Since you've had a problem before, Take your time and clean every connection you can find. Use an electrical contact cleaner with a real small brush in the female socket. To help preserve the connection and to aid in reconnecting the plug I use an electrical lubricant.PJ /ubbthreads/images/graemlins/thumbsup.gif

 

[DrEntropy]

/ubbthreads/images/graemlins/iagree.gif You will most likely find it to be the tail-light circuit connection at the firewall: Lucar gang connector. Red wires if memory serves.

 

[wkilleffer]

I cleaned the fusebox and the underhood connectors. I used my multitester to check conductivity between the fusebox and the underhood connectors, and all seems to be well.

After cleaning up in the trunk, I checked conductivity in those connections, and they seem to be ok. The grounds seem fine now.

The problem is that the lights still don't work. My tester won't reach from under the hood to the back of the car. But it seems unlikely that there would be a wire break since the harness is so new and the other lights back there are ok. Strange things do happen, though. I'll figure out a way to test that as well.

I'm starting to switch new bulbs in. Is this a series setup where one bad bulb can take the whole system out? I wonder if my sidemarker bulbs might be bad, especially since I don't have any spares right now. The new brake/tailight bulbs didn't make a difference.

Thank you for the advice so far.

 

[tony barnhill]

Check inside the light fixture to see that the little cardboard 'thingee' moves up & down...when you take a light out, it should move outward - when pushing light in, it should move inward

 

[jcatnite]

You can also check voltage at the individual light sockets with a multimeter. It's a common power supply that is the issue since the ground is working if you have brake lights but no running lights. I'm pretty sure that if you follow any of them back you would have to run into a common connector for all 4 positive wires. I would check for power at that connector and work my way back from there. I don't think that one bulb being burned out will affect the others. They might have a common ground but not a series type power supply.

 

[jcatnite]

Ooh Ooh, wasn't there a link here a couple of months ago to some web based wiring diagrams for MGB's? Might come in handy in this situation. Just a thought.
JC

 

[RomanH]

For stock schematics you can go to Dan Masters' web site.
https://www.advanceautowire.com/

Hope you get your issue resolved quickly and easily.

 

[wkilleffer]

I could all but write a book about the things I've done in the last three hours. But I have to throw in the towel for further endeavors until tomorrow because I have to get up and go to work.

Anyhow, I have continuity from the fuse box to the back of the car on the red wires, which are the ones that power the taillamps.

I've cleaned more connectors than I care to think about, including the ones coming off of the alternator. All the bulbs check out ok. The grounds on the taillight assemblies are now clean. The spring tension on the bottom of the bulb sockets is good all around.

Also, I removed and cleaned the ground areas for the front turn signal lights, as the parking lights up front aren't working either. Thought for sure that would cure it, but no dice.

It's starting to look like this is a problem where "juice" isn't getting where it's supposed to. Maybe it's time to look at the wiring from the front side of the fuse box. I have circuit diagrams and a Bentley manual, but that part of the system is getting into new territory for me.

I've got my work cut out, but not until tomorrow. Keep those cards and letters rolling in. Thank you for the ideas so far.

 

[jlaird]

Did you check the bulbs, how about the contact of the bulb to the connector. Always seemed to have a bit of a prob with those.

 

[mgbmedic]

Here's another thought...Check at the fuel pump(if it's a late model whereas the fuel pump is under a metal cover in the trunk)the rear harness is wired hot at the pump. Check the ground at the capacitator(blue color on my 76)I had a similar problem as you described and found the ground was bad here. Also, my fuel pump was dead do to the bad ground.

 

[kennypinkerton]

Keep at it!... Your getting close to not having any electrical problems by cleaning all the connections... Plus you'll be better able to diagnose future elctrical problems by knowing your electrical system better than ever!

 

[Bruce74B]

Have you checked the switch? or the connections to the switch? Has someone added a relay to the headlights and do you have a loose wire coming off the switched side of the relay to the other lights? A multi-tester at each connection should trace the power supply to see where the power is availble. You might also try connecting a FUSED jump wire from a known hot power source to the connection at the bulkhead and see if that lights up your lights and narrow the search to the engine compartment or the dash board.

Bruce /ubbthreads/images/graemlins/cheers.gif

 

[PAUL161]

I'm not saying that this is the problem, but I thought I'd throw this little piece of info in the pot. I had an interesting situation that happened to the lights on my car hauler. I lost my left turn signal and the 4 ways wouldn't work. When I turned the 4 ways on, the electric brakes would make a funny noise. Also when I turned the left turn signal on, the electric brakes would surge. Problem was a burnt out bulb. The bulb looked like new but, as the bulb wasn't grounding because of being blown, the system was looking for another ground and went to the brake system. Sounds crazy, but a new bulb made everything right. Needless to say, I now carry extra bulbs for the trailer.PJ /ubbthreads/images/graemlins/thumbsup.gif

 

[wkilleffer]

[ QUOTE ]
Have you checked the switch? or the connections to the switch? Has someone added a relay to the headlights and do you have a loose wire coming off the switched side of the relay to the other lights? A multi-tester at each connection should trace the power supply to see where the power is availble. You might also try connecting a FUSED jump wire from a known hot power source to the connection at the bulkhead and see if that lights up your lights and narrow the search to the engine compartment or the dash board.

Bruce /ubbthreads/images/graemlins/cheers.gif

[/ QUOTE ]

I looked at the switch and cleaned the connections there. Not sure how to test it. I installed it myself three years ago, and it was new out of the box. Same goes for the hazard switch. Doesn't mean it's perfect, but it doesn't seem that it would have failed at this point.

AFAIK, no one has installed a headlight relay. Frankly, I wouldn't know where to look for it if they had.

A fused wire is what helped me to get the back lights working when I first got the car nearly five years ago. I was able to patch and jury rig the botched wiring back there until I could purchase and install a new rear harness. The main harness is next, but doesn't look nearly so molested.

 

[wkilleffer]

[ QUOTE ]
Did you check the bulbs, how about the contact of the bulb to the connector. Always seemed to have a bit of a prob with those.

[/ QUOTE ]

How do I do that? Everything *looks* like it should be ok, but we all know how that works sometimes /ubbthreads/images/graemlins/crazyeyes.gif

 

[wkilleffer]

[ QUOTE ]
Here's another thought...Check at the fuel pump(if it's a late model whereas the fuel pump is under a metal cover in the trunk)the rear harness is wired hot at the pump. Check the ground at the capacitator(blue color on my 76)I had a similar problem as you described and found the ground was bad here. Also, my fuel pump was dead do to the bad ground.

[/ QUOTE ]

My car's a 74, so my fuel pump hangs out down around the right rear fender. But it's funny you should bring that up. Before I tore into all this, the car would act like it was heat soaked and fuel starved when I started it up hot, and its idle speed was getting inconsistent. When I cleaned that big ground in the trunk by the license plate, that sort of behavior stopped. I was only getting about 14 mpg while that was going on as well. Funny how something like that can take the whole car down.

 

[wkilleffer]

[ QUOTE ]
I'm not saying that this is the problem, but I thought I'd throw this little piece of info in the pot. I had an interesting situation that happened to the lights on my car hauler. I lost my left turn signal and the 4 ways wouldn't work. When I turned the 4 ways on, the electric brakes would make a funny noise. Also when I turned the left turn signal on, the electric brakes would surge. Problem was a burnt out bulb. The bulb looked like new but, as the bulb wasn't grounding because of being blown, the system was looking for another ground and went to the brake system. Sounds crazy, but a new bulb made everything right. Needless to say, I now carry extra bulbs for the trailer.PJ /ubbthreads/images/graemlins/thumbsup.gif

[/ QUOTE ]

I'm going to go stock up on all the bulbs today and switch them all out to see if that helps. One of the front turn signals has a yellow bulb in it, and I don't remember putting it there. It might be due for a change.