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Electrical problems

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rabauer

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First off, let me apologize if this is in the wrong forum. I am new here. I am working on a 1977 MGB. Overall, a very solid car. While driving down the road the other night smoke started pouring out from behind the steering wheel. Making a hasty exit to a safe parking spot, I shut everything down. The smoke subsided. I re-started the car and all seemed ok except the headlights were not working. I managed to get home without headlights. When I took the covers off behind the steering wheel I found the red wire with green tracer melted. The blue and brown wires were OK. I dis-assembled the headlight switch and it does not appear that there was a problem with it. When I put a jumper between the R/G wire and the brown wire, all gauge lights and running lights come on w/out anything heating up. Jumping the R/G wire and blue wire, nothing happens. I suspect this is the headlight circuit. This car has halogen light bulbs and what I think are two headlight relays mounted on the left side inner fender. I cannot find any blown fuses in the fusebox mounted on the fender well. Having said all that, I am wondering what caused that to happen, and where do I begin to look for the problem?
 
Welcome, this is the RIGHT place - you have found us!

As I'm sure you are aware electrical problems abound with the LBC.

Considering we are driving 30+ year old cars, it's small wonder. Of course many stories have been published about that magic Lucas smoke that escaped from your car. The answers will vary a little, but will be of a theme.

Replace the burned out wiring, the melted connectors, put in a fuse or two - WTH not?

Some have put in elaborate relay systems to run their lights on separate and new circuits with heavier gauge wiring that provides better current to the bulbs while at the same time less heat to the loom.
Maybe you have some in line fuses that you haven't found yet?
 
As a pre-emptive "strike" I'll suggest this as a source for a diagram for reference:

https://www.advanceautowire.com

They have a good schematic section there where you can find the diagram for your particular year.

Red/green is getting power from the headlamp switch and powers dash lamps and the left side marker/parking lamps, IIRC.
 
And by the way: WELCOME TO THE FORUM!!!

We will usually have an answer for your question quickly: sometimes it'll be in minutes. There are some of the most dedicated, knowledgable LBC enthusiasts on-planet on this forum, all willing to lend a hand with as much info as possible.

Ask away, and enjoy!

BTW: ~Some~ of the info you may get ('specially from moi) may be sideways. ALWAYS confirm with double checking your particular car... as Rick says: these beasties have been "out in th' wild" for thirty+ years. No tellin' WHAT has been done to 'em... and we thrive on photos. /bcforum/images/%%GRAEMLIN_URL%%/wink.gif /bcforum/images/%%GRAEMLIN_URL%%/laugh.gif
 
Welcome to the forum. WHERE in NC are you? I'm in Durham. The MG car club is fairly active in this part of the state, NCMGCC. If you're not too far away, there are many in this area who would be happy to help you sort this out
 
Hi Doug! I'm in Greensboro. I'm really at a loss right now because I can replace the wiring, but that does not tell me what caused the problem. More importantly, the headlights no longer work. I will dig into it deeper in the next couple of days to see what I can find.


Ron
 
Look to the switch, Ron. It has to pass electrons forward.

And by all means hook up with NCMGCC and Doug if possible!
 
Ron, I'm probably about an hour or more from where you are. Unfortunately I won't be able to commit time to travel until after the holidays. If you're trying to fix this problem between now and the end of the year, you may want to search the UserList here for user "LastDeadLast" (a.k.a. Shannon). He owns a '72 TR6 and he's in Greensboro. It's been a while since I've corresponded with Shannon but I think you'll find that he can help you sort this out. Yes... he's got a TR and you've got an MG, but a lot of the Lucas wiring is similar if not common between the two. The electrical problems certainly are common!
 
/bcforum/images/%%GRAEMLIN_URL%%/driving.gif I'm pretty sure the Lucas smoke is interchangeable between the Triumphs and the MGs. But as stated above, the electrical fun never ends with the LBC's.
 
rabauer said:
Hi Doug! I'm in Greensboro. I'm really at a loss right now because I can replace the wiring, but that does not tell me what caused the problem. More importantly, the headlights no longer work. I will dig into it deeper in the next couple of days to see what I can find.


Ron
Click to expand...

Tools needed:
test light or multimeter
wiring diagram

The brown wire is the power input wire to the headlight switch.

The red/green wire is the power output wire from the headlight switch to the tail lights, dash lights, and marker lights.

The blue wire is the power output from the headlight switch to the turn signal switch. The blue wire branches into the blue/white wire for the high beams and the blue/red wire for the low beams.

Make yourself a couple of enlarged copies of the wiring diagram, one for reference, and one to keep track of your progress as you check the circuit. Wiring diagrams are available at https://www.advanceautowire.com click on "stock schematics". If your car has an ignition relay, use the diagram for "1978 and later from Bentley"

Using your meter or test light and the wiring diagram as a road map, test the various connections and switches in the headlight circuit until you find the fault. Common problems are high resistant, corroded connections, that generate heat and burn up. Look for areas of the harness that may have been rubbed or pinched and are now shorting.
 
Personally, I think that the car was simply trying to break him in. It's just not right to drive a vintage british machine without ever having had an electrical disaster on the road, accompanied by smoke and melted insulation. Consider this a rite of passage.
 
A roadside failure does seem to be required for initiation... kind of like your car is hazing you.
 
Roadside failures caused by the electricals giving up their Lucas smoke usually happen at night! That's why a toolkit containing a fresh flashlight and a cell phone is an indispensable part of LBC motoring. My initiation with a 1971 MG BGT was when the hack the DPO installed to get power to the coil lost its duct tape insulation, allowing the bare wire to contact the frame and melted the wire from that point back to the ignition switch. Lots of sweaty summer fun under the dash to get that one fixed.
 
Daimlerdb18 said:
Roadside failures caused by the electricals giving up their Lucas smoke usually happen at night!
Click to expand...

...in the rain, far from a pay phone (or cell tower) when you are all dressed up in your finest white tuxedo and late for the wedding.
 
OK folks.....I get it. It is like owning an old Harley. First you work on it, THEN ride it. I have got it sorted now thanks to all your help. The new switch is on the way, and I now have a wiring diagram even I can read! (thanks for the link DrEntropy). I am looking at the wiring system a little at a time and hope to find the culprit soon. I have to say that this is one of the funnest cars I have ever driven. I think in the grand scheme of things I will end up with this car as my very own. I also have a neighbor that has one under a tarp a few doors down. I intend to go talk to him to see how little he will take to remove that "eyesore" from his driveway :smile:. I still have one question. I don't have to give up my Harley to become infected with the MG, do I?
 
Not at all! The have been known to cohabitate quite amicably! /bcforum/images/%%GRAEMLIN_URL%%/wink.gif
 
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