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MG MGB Technical - electrical problem - voltage regulator?

I recently bought a '68 BGT. Almost everything electrical does not work. This made me think fuse, so I checked them and sure enough one was burned out (the one with all the green wires). I replaced the fuse, but nothing started to work.
The following items do not work:
-All gauges
-All lights on gauges
-Brake lights
-Reverse lights
-Turn signals
-Hazards
-Horns
-Windshield wipers
-headlights (think that one is due to the switch, as the highbeams do work)

The following items do work:
-Starter
-Ignition (car runs)
-Ignition light (turns off when engine is running)
-fuel pump
-Highbeams

Since there are so many things not working, I am thinking there is some common thing that they all run through. I think several of the items run through the voltage regulator. Might that be the problem? Also, is the control unit the regulator?
Steven J. Korotky

WOW! Sounds like the PO did not pay the electric bill!

Was the car sitting before you got it?

At first guess, it sounds like a lot of the electrical connections are dirty and corrorded. FDid the PO leave the wiring "as stock" or did he make "improvements".

If all the bulbs are good, then it's just a matter of cleaning and/or replacing all the places where there's electrical connections.

Was the car from a near a coast location? The salt spray has a bad effect. I know it's real humid down there. The regulator is more of a control for keeping the battery charged than for actual distribution.

That's the best I have to offer with info supplied. Good luck.
glg

Steve, The B's wiring harnes has more bullets (connectors) in it then the local gun shop. Get a rag, q-tips and some WD-40 and start cleaning. Start at the fuse block. the block can corrode enough to keep a new fuse from making contact.

then get a wiring diagram a nd volt meter. Let us know where you have or dont have power and we can be of more help.

D
Doug Gordon

I don't think your voltage regulator is the problem, since the red light goes out with the engine running it soundslike the charging circuit is ok. If you do not have access to a multimeter, you need to buy or borrow one to find out which voltages you are missing. You can also use atest lamp for checking the presence of voltage sources. You will also need a workshop manual with wiring diagrams.

With your high beams working the light switch is good. Look in the dip switch or associated lo beam dip switch to lo beam filament wiring for the problem.

Based on what is not working, it appears you are missing 12 volts at the output side of both fuse box fuses on the purple and green sides. I would start by checking for 12 volts at those points. If you have 12 volts at the green or purple wires you need to go toward the circuits and check for 12 volts to find your problems. If you do not have 12 volts the problem should be somewhere in the fuse box or the input white or brown wires, I think inputs are ok as the white feeds the coil and fuel pump, the brown feeds the ignition switch and headlight switch. The fuse box fuse clips can cause problems if they are not clean or have lost tension.

Good luck and get back with additional information you may find, Clifton
Clifton Gordon

Just a side note --- locate the black wires, (grounds) and clean the eye-ring and the metal for the ground.

There are quite a few under the dash that could be the culprit.

You might consider replacing all the bullet and spade connectors as a project to eliminate present and future electrical problems. Sort of a do it once and do it right general maintence project.
glg

Another side note is for you to purchase one of those gizmos that lite up as you trace wires. Connect it to ground and then you can follow the 12 volts through the car and is easier (cheaper too) than a voltmeter.

CW
CW Strong

Steve: Replace the fuse box. Its cheap and easy. I did this with my 69. As noted above the contacts corrode and also weaken with time to the point where a good contact with the fuse is difficult to achieve.
How far you go after that depends on how bad the corrosion is.
Andrew Blackley

The car was sitting for a long time. I think it was 14 years. I guy I bought it from said that it was driven for about a month about 3 years ago. The car was cheap, big surprise, but it was the only GT that I found that I could afford. what is a poor college student to do?

The car was garage kept so there isn't much rust, but with the florida humidity I'm sure that the connectors could be corroded. I did notice that the fuse box looked pretty sad so I guess I'll take it out and give it a good cleaning along with all the connectors that I can get a hold of.
Steven J. Korotky

Steven:
Get yourself a copy of THE original factory wiring diagram for your 68 MGB GT. If you are in doubt about how to get a copy (library, buy a Bentley Factory Manual), I can email you one as I too have a 68 GT. This year had a few firsts added to it (alternator with a separate voltage regulator was one) so you need to have some way to trace your wiring to make sure that what works is actually the OE harness and not some makeshift wiring someone slapped in just to get the car mobile to sell.

You will need to know the correct colors and pathways of the various circuits if you are going to trace out the problems you seem to have, and it does seem possible that a good place to start would be a new fuse box. They are cheap, available, and if you move only one wire at a time from the old to the new, pretty simple to replace. Any car this old that is still using the original fuse box is deserving of a new one since the innards are only riveted together and subject to much corrosion over the years. If you do get a new one, I would also recommend soldering (with a non acid flux solder) all riveted connections on the back side of the box. This will give you about as good a connections as you can hope for and they will last a lot longer than if you hadn't.

I hate to raise the spectre of a melted harness, but given the laundry list of things you have that don't seem to work, I think you have to be aware that this is possibility, even if a remote one. This is why I said what I did at first about possible added wiring to make the car run. Hopefully, it will be just crappy connections and moldering, crumbling Lucas barrel connectors that no longer hold the bullet wiring ends tight or at all or are full of corrosion. I was a college student with an old british sportscar once too, and I hope it is something simple and cheap, and not a need for a replacement harness. Good luck and email me if you need that wiring diagram.
Bob Muenchausen

In the first order of parts from Moss, I made sure I got the bentley manual. Its been a big help so far and I'm sure it will continue to do so.
Can you confirm that the wiring diagram for my '68 BGT (U.S. spec) is Diagram 7 on page 319 and not #3 on page 315. my car's # is 149933 so the # fits both, but I didn't see the oil pressure sending unit and rectangular pressure gauge in diagram 3, and my car has them.
From what I can see of the wires, they look to be 99% stock and without damage. The only thing that I have noticed that was spliced was an 8" piece that goes to the oil pressure sending unit.
If it comes down to it, can a new harness be put in without taking the whole car apart? I'm living in an apartment, in which I am technically not allowed to do any maintainence on my car, but with a little sweet talking I got them to let me work on it so long as I don't spill fluids, don't spread parts all over the place, and clean up by the end of the day.
Are there any tips on where to start and in which direction (component to source of power or vice versa) to test? My guess is power source to component.

-Steve
Steven J. Korotky

Diagram 7 is correct for US Cars. The best place to start in your case is at the fuse box since the components on the power side of the fuse box seem to be working. Good luck

Clifton
68 BGT
73 B Roadster
Clifton Gordon

Steven,

All the above thinking is good. But I also suspect there may be just ONE poor contact causing your problem.

Our fine cars are susceptable to poor grounds everywhere. If it was theoretically possible to ground something cheaply, they went for it.

Please let us know what you find. My MGB also has no headlights EXCept it has high beams. So I am most intrigued.

Daryl
Daryl

Yeah! Check all grounds first. They are the most suseptible and many items on your list could be the result of one or two bad groundings.

Like that old Chinese proveb says: The workings of a Lucus electrical system starts with one connection at a time ---
or something like that!
glg

I agree with everyone, It sounds like the green and purple circuits' grounds, which go behind the dash and under the car to the rear and to the lights in front, lots and lots of grounds. Some of the wiring harness under the car is exposed along the frame rail on the right side, then to the boot. That being said, It is possible, even having been stored in a garage, that somewhere along the harness that critters have been at work gnawing on the PVC tape and insulation. This causes interesting things to happen when wires touch, or loose ground or intermitent ground. (blown fuse, etc) The Haynes manual has wiring diagrams as well.
Copy it on a copier that will blow it up, it's easier to read.
TDHoward

Been in your (Apt.) situation before, and I think that it is likely that much of what you need to do can be done without either a new harness or a sprawl of parts/tools in your parking lot/garage space.

I would follow the other guys' suggestions to trace out the grounds first, and establish good contact with a little bit of sandpaper to clean up the ring connector-to-body panel connections. If none of those are your culprits, at least you will then know that they good, regardless. And you should put a smear of Dielectric grease (in a tube at the auto parts store - buy a bigger tube as you may well need to use it elsewhere for all your wiring connections) on every surface to help keep it clean and working properly.

I would suggest that if your budget can afford it, get both a 12 VDC light bulb-type continuity tester AND an inexpensive little Volt/Ohm meter (Radio Shaft, Sears) for tracing out your wiring. It will be a very good Long term investment. Sometimes you will want to check the continuity of a piece of wiring from end to end, and on occasion, checking for voltage (which you can do with both a light and a voltmeter) is not the way to check out the integrity of an individual length of wire or connector as will be testing for resistance (hence,the ohmmeter). Do not, however, bother with a digital volt/ohmmeter as the older mechanical type will actually serve you better for most all automotive uses. And often, they are cheaper and more rugged.

Gordon is right about the #7 diagram, and having the Bentley Manual was a wise buy all around.

You may find, as many of us have, that poor connections are your biggest enemy. If you have the time, you can buy the Lucas barrel connectors from Moss (LBCarCo) http://www.lbcarco.com/ or Triple-C http://www.triple-c.com fairly cheaply, and then over time replace them in the comfort of your own car (I am being facetious, lying on your back working up under the dash is a pain!) without alarming the landlord. Those of us who have gone through this drill are very grateful many years later for the time and effort and the little bit of money spent to clean up the connections. Lucas barrel connectors are notorious for literally crumbling away, so replacing them is a good idea any time, any where.
Bob Muenchausen

Bob Muenchausen Wrote:

"Do not, however, bother with a digital volt/ohmmeter as the older mechanical type will actually serve you better for most all automotive uses. And often, they are cheaper and more rugged."

I concur with Bob on this. For your purpose, a cheap VOM will work just as well as an expensive one, but when you destroy it by dropping it, or by measuring volts on the ohm scale, or some other stupid thing, it doesn't hurt as much.

And you will destroy it, sooner or later. Voltmeters just don't last long around an automobile. I have a small graveyard of dead VOMs in my shop. All cheap ones, think goodness.
Dan Masters

Steven: I like to take a bit of time allowing fix-it conundrms bonce aroud in the dartk recesses of my bay cave mind - jus to let things fall on my mental work-bench.

You posted that:


The following items do not work:
-All gauges
-All lights on gauges
-Brake lights
-Reverse lights
-Turn signals
-Hazards
-Horns
-Windshield wipers
-Headlights (think that one is due to the switch, as the highbeams do work)


There is a junction of 7 black ground wires that go to windshioeld motor, the heter boster fan, the minus terminal of the alternator, the directional dash bulbs, panel lamps, cigar lighter and a few other things.

Go to the Voltage Control box -- locate th black ground wire and trace it back to where seven witres are conected to an eye connector that is bolted to the frame.

You'll find that those six wires will branch out to other items that rely on that first grounding. I believe you'll find that major junction of black wires under the dash, and it it the one thing that has all of your failed items in common -- sharing the same ground.

good luck
glg

This thread was discussed between 16/09/2003 and 18/09/2003

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