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MG MGB Technical - Electrical – Starter – Alternator - Charging Problem

If I scratched my head any more I would be scratching my knee joints.

This is a long one. It has also been a long irritating issue. If I was not one of the thousands of IT people who are amongst the temporarily early retired ($920 per mo is not considered enough in the SF Bay area to retire on) I would take it to Hillary Reddy to sort out.

About one block after I made my first right turn on my way home at 2 AM a couple of weeks ago my fairly-fault free 1970 B roadster suddenly dies. No engine, no lights, no sign of life what-so-ever. After checking a few things I determine that the problem is due to one of the small brown wires coming off of the starter solenoid. From the schematic it appears to be one of the ones that goes to the fuse block. After doing a Disney repair, I was able to start it and get on my way at 5 AM. No problems at all getting home. Oh, the day before this happened I had the oil changed. Shouldn’t be relevant, but……..

After repairing the connector that was bad I was able to again start it without problem. I decide to get a quick beverage with a friend of mine before making a full night of it, again no problem starting it. Go to leave the establishment we were visiting and all I get is a clicking noise (I find this is the common symptom of a very low battery). Thinking it is another wire that was a little dodgy looking, I try to repair it (not the problem). I get someone to help bump start it –we are off! As I am driving home it sputters a small bit, the oil pressure starts to decrease, as does the engine temp. Just as I start the freeway entrance it dies. Although it wasn’t known at that time or for the next couple of days, it appears that the battery is totally dead.

Now I remove and clean the solenoid and the starter. Fix any wires that are dodgy looking thinking they might be the issue. Get a battery jump and go around the block once and it dies again. Get a jump and drive it home and park it. Hmmm, purchase a new alternator and new fan belt (was looking a bit ancient). After another jump I let it run for a small bit while watching the battery voltage decrease (voltmeter was attached) and then the engine dies. During this whole time that little red light is full on.

I do some more reading in the Electrical section (www.mgcars.org.uk/electrical - FANTASTIC!!!) and find that the red warning lamp will be on if there is a difference between the alternator output and the battery voltage. I purchase a battery charger and give it a full charge. Now the light is dim. I need to do a 30+/- mile drive with the lights on now. On the way, the light is really dim, super bright, dim, bright, and everything in between. Once at my destination I turn the car off and am able to restart it. A few days later I return to the car (car was parked at airport using airport transfers sevenoaks parking) and decide to be smart and hook up my voltmeter for the drive home. During this drive the light brightness is all over the place again and the voltage at the battery seems fairly consistent at 11.5/12 volts. It is only when I get within 8 miles of home that the light is steady. Now the oil pressure gauge is dropping (25 lbs.) and the engine temperature is dropping. I then notice that the voltage is dropping. The MG was very nice and came to a rest as I pulled into my parking space.

After another full charge and a short drive I noticed something. It appears that the brightness of the light sometimes changes when I go over bumps. The voltage really only drops when the head/parking lamps are on (doesn’t matter which position).

I am now going to see if I can find any loose wires which may be related to this. Thought I had caught everything before, but maybe not.

Some previous observations that I have had with my Honda replacement.

- I used to believe that the red warning light was a low oil pressure indicator. Whenever the oil pressure dropped below 50 lbs. it would dimly come on. This would only happen when at idle. Based on how that light works, I can understand it.

- The headlights stopped working one evening. I tested everything without luck. I removed the stereo (which was intermittent) and they worked. At first perfectly, then only with high beams (thank goodness for weak lights). It has been like that for nearly 8 months.

- The turn signal switch is a bit “worked” looking. Looks as if some PO decided they were going to do some funny repair to it. The horn part of the switch hasn’t worked and does not complete any kind of circuit. Since there were tabs broken off of the horns themselves, I removed them.

- There seems to be different wires than what the schematics. On the power side of the solenoid, there are four brown 12 AWG wires, a brown 8 AWG wires, and a big black wire coming from the battery. Based on the schematic, there should only be two brown 12 AWG wires. One to the fuse block and one to the starter.

Anyone else ever encounter funny electrical behavior? Any wires I should look at specifically? Anyone want to trade straight across with a brand new MINI Cooper S?

Thanks all!
Jason
1970 mgb roadster

PS: Regardless of what the manual says, you can take out the starter without removing the distributer on this car. After removing the starter's bolts and wires you tilt the back up, give a little twist, and down it drops. Best if done from the underside of the car.
Jason Coolbaugh

Jason,
I hate to say it, but I'm glad that there is some one else in Oakland suffering as hard a time with the starter as me. Refer to the "2 different starters" thread to catch up on my grief, which I also think may stem from the starter solenoid. Actually if you have any interest in swapping starters for a brief moment to see if that fixes either of are problems let me know. Mine is a "brand new" rebuild. Any how I have 4 brown wires also, and an additional yellow that I ran from my alternator (which is a Bosch conversion). One of the brown wires is actually a double wire run to one connector (if that makes sense). I don't know what AWG each of the wires are off the top of my head, sorry. But some times people double up the wires to one place to get a better connection, as I did with my Alternator.
Give me an email and we can exchange numbers perhaps.
Bill
Bill Mertz

Jason - All of this simply points to the alternator not charging the battery or running the cars electrics when under way. You should have about 14v on a brown, white or green when running, 12v says you were running on the battery until you flattened it. Given your original problem it *could* be that the brown from the alt isn't making a good connection at the solenoid stud, but the rest just indicates a bad alt.
Paul Hunt

I will take a look at the wires leading from the alternator to the solenoid stud again. I will see if the local AutoZone has some of the electrical "grease" to help with the connections as well.

The intermittent behaviour of this is what baffles me. About seven hours ago when I drove it the warning lamp never changed. Always stayed bright. Whereas the day before it was all over the place.

Thanks for the help!

Jason
Jason Coolbaugh

One thing that happened to me a few years ago when I changed the alternator on my '73, is that despite the plastic plug on the harness for the alternator, the connectors were sliding down along the sides of the terminal spades on the alternator which caused all sorts of intermittent weirdness until I happened to find it.

Wayne
Wayne Pearson

As Wayne mentions, check the condition of your wiring connectors. Many faults occur where they are not readily visible, and as mentioned, your situation certainly points to a random intermittent which is usually indicative of a crummy connection or connector.
Bob Muenchausen

Wayne & Bob: You mention plugs, about 6 or 8 months back after a good 100 mile run in my 74
I stopped near home to gas up. t When I left the station the alternator warning lamp wouldn't got out below 2500 rpm. I said bad alternator, replaced it with a spare and it worked ok the next 3 or four times I drove the car. The next time I drove it the light would flicker at normal road speeds but was ok at idle and low speeds. Being lazy I changed alternators again, I had three spares, but had the same problem. I took the two alternators I thought were bad to a repair shop and they checked ok.

I got out my multimeter to do a little circuit testing, I pulled the alternator plug off and removed the
terminals from the plug and noticed the big terminal on the heavy brown wire would spin around
without twisting the wire, it was ready to fall off. The terminal and wire end were very brittle. I cut the
lead back to good wire, soldered another terminal on and everything has been fine since, and I still
have some good spare alternators. You are right it's sometimes the small things. FWIW, Clifton
Clifton Gordon

I'd definatelly check the plug connections. Take it out of the alternor and pull the wires out. It takes a little patience and a small screw driver. You can visually inspect them quite easliy and also check with a multimeter. As for the 12V your getting, this is way low. It should have 14V and 12.5+V with the headlamps, radio, and fan on. You can charge you battery and start the car. If the plug is mot connected if you use a voltmeter you should get 14V at the largest terminal, also the largest wire. I really think it is a bad alternator.
To answer some other question, your oil pressure gauge is mechanical and is not related at all to the battery voltage.
The red light will sometimes go on at idle, but only because the alternator is not putting out enough current causing the voltage to drop to a low level.
The brown wire you are descibing may be an unfused circuit, so you want to make sure you repair it well, or you might have a melt down. The wiring diagram for my car(73) has 4 wires coming out of the solenoid. Two large wires, one to battery and one to alternator, and two small wires, one going to the alternator and one going to the fuse block, by the way of the hazard, ingntion and headlamp switch. You can see my dilema in "electrical nightmares' as I dicovered how these wires were unfused.
Hope this helps
John
J Arthurs

I HAVE FIXED IT!!!!

The other day I did three things. Since the switch for the high beams was a little funky I decided to just use a wire nut to connect the two wires until I can replace the turn signal/high beam/horn switch stalk. Rent is more of a concern these days. I also moved around one of the wires on the starter solenoid and the plugs that go into the alternator. The light went out. But then of course at 3 AM when I was returning home that night the light came back on, then off, then on. Hmmm, must be a loose connection.

After assessing what was probable I narrowed it down to the plug that has the brown wire, two yellow and brown wires, and the other one (not sure what color it is). Anyway, the plug was a little dodgy so I removed the wires and connectors, put some shrink tubing around them to insulate them and re connected them. The little red light is now out.

Also, I checked the voltage coming off the alternator and found that it was coming out somewhere in the 14v area. So it had to be something other than the alternator. I can now say that it is fixed.

Thanks to all who had suggestions and recommendations!
Jason Coolbaugh

This thread was discussed between 31/07/2002 and 04/08/2002

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