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A wiring question. no really, i know it's hard to

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Rob_P

Rob_P

Jedi Trainee
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believe.....

OK, my lights seem to be screwed up, and i am in the process of checking my grounds. curious if this problem rings any bells or gives any indication where to start.

this is on my 76 B
problem 1:

the blue wire coming into the headlamp dip switch on the colomn is hot all the time. 12.5 volts when the key is off.

with he key still off and the high beam lever towards the driver (at rest, not held in) the headlights are on (it is the Blue with white wires that are hot at the headlights), no parking lights, just headlights.

push the lever forward and the lights go off.

Also, this is happening with the light switch unplugged.

More fun, at the switch, only the brown wire is hot (not the blue which from the schmatics, looks like it's a clear path from the switch to the high beam dip switch on the column.

When i connect the Brown to blue (via switch or jumping) nothing happens, everything seems to be the same as before.

When i connect the Red w/ green wire to the brown (via switch or jumping), all the lights come on as well as the ignition circuit. Fuel pump comes on, car will run with this switch on and the key off. (figured that out the hard way!)

Not sure where to start as i don't know if these are related or two seperate problems.

as always any help would be greatly appreciated, as i know you guys hate talking about these silly little cars. /ubbthreads/images/graemlins/grin.gif

Thanks,
Rob
 
I don't know the wiring specifics for a '76B but can offer the following general LCB comments.

The power to the solid blue wire for the dimmer switch should come from the on/off switch for the headlamps. So, the blue wire on the dimmer should only be hot when the switch is on. The position of the dimmer switch will determine whether the blue/white or blue/red wire going to the bulbs is hot.

Others will have to provide MGB specific information.
 
If you haven't already done so, check out Dan Masters' schematics at Advance Auto Wire ( https://www.advanceautowire.com/ ). Click on the "Stock Schematics" link on the left-hand menu bar and you can download a PDF file containing about the best info readily available.

You can also check out the "Bee and Vee" pages ( https://www.mgb-stuff.org.uk/electricstext2.htm ) for some good info. They have some easy-to-read schematics broken down by major system that can serve as a good summary of the information in Dan's diagrams.

R.
 
Re: A wiring question. no really, i know it's har

Thanks,
I have the pdf from advance autowire (i got the link from another post of course.)
the other link looks great for trouble shooting as well.

i think i have 2 seperate problems. so first i will chase down the blue wire and find out where it is getting it's juice from.

then i will play with the red wire.

i think my first step there is to seperate the 2 reds coming out of the switch and see if th problem is in the parking lights or the instrument panel.

thanks again,
rob
 
Re: A wiring question. no really, i know it's har

Aha,
part one has been solved (but not fixed)

The high beam dip switch is not working properly, hopefully this can be rebuilt.

the connector is out of alignment, so when the lever is in the "low beam" center position, the connection is being made to the "flash" (forward pull) which is why the high beams were on when the ignition is off, it's as if someone is pulling on the high beams all the time.
for now i can keep the lever in the high beam position and the connector will not touch anything.

Now i just have to figure out which Red and green wire (parking lights or instrument/gauge ligts) has the short.

with the parking lights on, the white ignition wire (fuel pump, etc) is hot.

i am going to check the parking light section of wire first.
i hope it's an easy find/fix.

(i think it's out of smoke!) /ubbthreads/images/graemlins/devilgrin.gif

Rob
 
Re: A wiring question. no really, i know it's har

HOO-BOY!!! Here we go again! /ubbthreads/images/graemlins/wink.gif

...by isolating the individual circuits you'll hunt down your gremlin and kill it in no time. Just on a weirdrandom brane-f**t... have you done anything to the passenger side floorboard recently? Reason I mention it is: In 1969 I put in some "patches" to a floorpan with pop-rivets... had a similar wiring oddity... yup! 19 year old with a 1/8" drillbit. I put a pop-rivet thru the harness. Lucky I didn't let th' smoke outta it BIG TIME.

...just a thought. HTH.
 
Re: A wiring question. no really, i know it's har

Smoke, who said smoke. Careful with that stuff, hard to come by.
 
Re: A wiring question. no really, i know it's har

[ QUOTE ]
In 1969 I put in some "patches" to a floorpan with pop-rivets...

[/ QUOTE ]

Ahh, the summer of '69. that's back when i could poop my pants with impunity!

Not sure what has happened with that passenger side floorpan, this car was "90%" complete when i bought it 2 months ago. Hoping that the PO was better a better mechanic then mathematician! /ubbthreads/images/graemlins/laugh.gif

Rob
 
Re: A wiring question. no really, i know it's har

I need to come over there for a visit. Check the loom along the passenger side all the way back for similar damage to what I've confessed to... Can't think of any other place where the fuel pump power and the parking light circuit are in proximity.
 
Re: A wiring question. no really, i know it's har

[ QUOTE ]
I need to come over there for a visit.

[/ QUOTE ]

any time you find yourself on this side of the bay, you are more than welcome. /ubbthreads/images/graemlins/cheers.gif

i work out of my home more often then not these days, so i am never far from the garage. (is that good or bad!?!)

I will be seperating the two RG wires and following the culprit from the switch.

although at first glance, one of the RG's did not look to good, looks like it's let off some of that famed lucas smoke once or twice in the past. so that is an obvious starting point.

it may very well take me to the loom on the passenger side eventually.

on the bright side, if i ever loose my key all i have to do is put the lights on and get a running start. /ubbthreads/images/graemlins/smile.gif
 
Re: A wiring question. no really, i know it's har

[ QUOTE ]
i work out of my home more often then not these days, so i am never far from the garage. (is that good or bad!?!)

[/ QUOTE ]

VERY good. Me too. Today was the first in ten I've actually had to don the HumanSuit and leave th' hovel. /ubbthreads/images/graemlins/smirk.gif
 
Re: A wiring question. no really, i know it's har

if only they were all this easy....

a brief history, the PO took the car apart for painting, then hastilly put it back together for selling.

the PO had switched one of the three white wires at the fuse panel under the hood with a white and blue wire (which i don't know what it is.

(haynes says they are white with brown, bently says they are white, mine are white)

so one of the white ignition relay wires was plugged into the parking light fuse.

now the question is "What is the white with blue wire?"

i don't see it in the schmatics.

any ideas, it's in the atttached pic, seems to be coming from the part of the harness that is going to the alternater.

Rob
 

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Re: A wiring question. no really, i know it's har

Kinda think it's -supposed- to go to a ballast resistor near the coil.

Good news that you found the hot lead iggy wire.
 
Re: A wiring question. no really, i know it's har

White with blue? Much too new for me. I haven't seen that code used on my LBCs.

Pop rivets I can relate to. The grille on the Mini is supposed to attach with sheet metal screws. When I put the grille back on after painting the car I ran one of those screws into the harness and scared the poo out of me. I hit the horn circuit.
 
Re: A wiring question. no really, i know it's har

mehheh. "blew yer mind"!?!?

...woulda blown mine, fer sure.
 
Re: A wiring question. no really, i know it's har

Rob P, No sure on your car. However, Blue with a White tracer is generally allocated by Lucas to the headlamps.--Fwiw---Keoke - /ubbthreads/images/graemlins/grin.gif
 
Re: A wiring question. no really, i know it's har

Blue with a white tracer is high beams (or solid blue for lighting "hot" leg to dimmer switch, or blue with a RED tracer for low beams), and would be lighting. White with a blue tracer would definately NOT be lights. /ubbthreads/images/graemlins/hammer.gif
 
Re: A wiring question. no really, i know it's har

Ever turn when you are doing something in the garage and set off the alarm on your car from the fob in your pocket. Same effect.
 
Re: A wiring question. no really, i know it's har

it looks like it wants to be attached to the power side of the parking light fuse. i believe it was switched with the problem white ignition wire.

i'll just leave it off and see what doesn't work /ubbthreads/images/graemlins/smile.gif
 
Re: A wiring question. no really, i know it's har

Rob this same problem has been discussed on this forum before you might check in the archives as someone posted the interconnection diagram. I vaguely remember it is associated with the ignition system in some form.--Fwiw--Keoke
 
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