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MG MGB Technical - Yet another electrical thread...

If anyone recalls, my '80 B has sat for about 7 years now.

The current issue I'm tackling is with lighting/blinkers. My headlights work, tail running lights work (the ones with headlights on).

However, my directionals don't seem to do anything at all. If I turn on my hazards, both dash blinker lights turn on but they stay solid and no lights outside the car turn on. I do recall changing the hazard switch with a brand new one from Moss/VB back when I last had it on the road.

Oh, and as a side note, after about 3 turn on's of the headlights, the switch seems to have fallen apart. Thankfully the lights were off at the time, so I'll have to investigate if I can get it back together or not as well.
Jeff Grant

And by the way, my tach jumps, but if I recall, it always did above about 2500rpm. In addition, it sometimes drops to nothing, but again did that back in the day as well.
Jeff Grant

Once again, my knowledge specializes in 72-74 midgets, so it might not apply.
The soldering in the tachs is not particularly robust; careful re-flowing of the solder could make a big difference.
I know that there were three or four different hazard switches in use... I wonder which one Moss copied? I also know that the wires, especially green, are easy to switch around. Is it possible you have swapped the two green leads?
David "shoulda hung onto a set of B schematics" Lieb
David Lieb



The new switches are junk. I have had 2 fall apart. On my most recent one, rather than replace it, I put it back together. The case had cracked so I put a wire tie around it and took some JB Weld and glued it up. It has been working since Feb with no problems.

If the emergency flasher switch is original to the car, it is possible that the internal contacts are corroded or the grease has dried out. A few vigorous flips of the switch will sometimes clear it up. You can rejuvenate the switch by carefully taking it apart, cleaning the contacts, replacing the dielectric grease and reassembling it.

There is the very slight chance the flashers located on the firewall behind the glovebox have given up but this is unlikely.

Corrosion has probably paid you a visit for your lights to not work properly. So time for a bit of maintenance.

First off, head over to http://advanceautowire.com and grab a copy of the wiring schematics for reference.

Next, pick up a can of contact cleaner and dielectric grease from Home Depot or Lowes. From a sporting goods store, pick up a .177 caliber wire brush.

Now, you are ready to start methodically checking and cleaning bullet connections. For grins, start at the back of the car. Disconnect each bullet connector.
Use liberal amounts of contact cleaner. Clean the male connectors with a bit of steel wool. Clean the female connectors with the wire brush. Don't go overboard. You just want to polish them up a bit. Then apply some dielectric grease and reassemble the connections.

While you are in the boot, locate the ground wire bundle. It is usually under one of the nuts that hold the license tag bracket on. Take it loose and clean the body under the eyelet so you get a good connection for the ground.

Head to the front of the car and repeat. Locate the ground wire bundle and clean where it is mounted usually under a screw near the fuse box.

I would recommend you clean the fuse box connections as well.

That should get the lights going. If not, check the bulbs to be sure they are ok. Grounding problems are a possibilty as well so check the fixtures to ensure they are properly grounded.

As for the tach jumping around - does engine continue to run properly and it is just the tach having a problem? If so, I would start by checking to be sure that the White with Black tracer wire is well connected at both the coil and at the tach. Also, check to be sure the green wire is connected to the back of the tack and has battery voltage to it with the key on. Finally, check to be sure the tach is grounded.
Oh, has the distributor been replaced at some point or do you still have the original electronic ignition model? If the dizzy has been replaced, what is in the car now and does it have points or is it electronic as well?


Good luck.

Pat Harrison

David and Pat, thank you for your replies.

I mentioned that I had replaced the hazard switch 7+ years ago as an FYI. It did work at some point, so I wouldn't immediately count it as an initial defective from the shipper.

I will go to that website and find the wiring diagrams.

Also, the distributor is original to my owning the car, so that's 11 years now. Again, it's sat for about 7 years as well. I remember similar issues with the tach going dead more specifically in the <2000 rpm range but that it would come back to life once the rpm was brought up while driving.
Jeff Grant

Okay, I've worked on the car some more without any success. Here's the details.

As far as my turn signals go...

1. My hazard switch had all wires secured properly. I pulled them and did the dielectric grease stuff and put it back together.

2. While greasing the hazard switch harness, I also greased all the other multi-wire weather proof type connectors under the dash.

RESULT: Hazard switch when turned ON continues to illuminate both dash turn signals as well as exterior lights. No flashing.

QUESTION: Since there's no flashing but the exterior lights turn on with the Hazard switch, could it's flasher be bad? I don't hear any ticking. The schematics say the turn signals have a different flasher, perhaps that one is bad from sitting so long as well?


As far as my headlight switch falling apart goes, I see how it works and should be able to super-glue it back together.


Side note, my windshield wipers don't work either... not sure if this is related. I remember back years ago that they wouldn't reset themselves to down and my mechanic had said it was a windshield wiper motor issue, but that didn't bother me since I didn't drive in the rain. Now they don't work at all so I wonder if the motor might just be gone completely now.
Jeff Grant



Jeff,

you are correct about there being a flasher for the turn signals and a flasher for the emergency lamps. Both are located under the dash behind the glove box.

For testing purposes, you can swap them.

If you suspect they are bad, you can pop them out and carry them down to AutoZone or Advance and get a couple of generic flashers for replacement. They probably will not fit the holder under the dash but will get you going. I think the cost is under 5 bucks each.

Can I assume that the turn signals are still not working either? Usually if that is the case, it is an issue with grounding. If they are not then:

At both the back and front of the "B" clean and securely fasten the Black ground wires to each turn signal assembly. Also, in the boot, all of the ground wires should be attached to one of the bolts holding the license tag on. Clean and tighten so you have a good ground. Then under the hood, locate the bundle of ground wires near the fuse box and clean and tighten so you ground them. Pull out the bulbs and clean the bulb bases and sockets with a bit of steel wool. Check to sockets to be sure they are not completely corroded away. When you go to put the bulbs back in, notice that they are keyed to only fit one way.

Once you get the lights going, then we'll tackle the tach and the wipers.

Pat Harrison

Hi Pat.

I already went through the ground in the trunk (attached to the license plate holder stud) when I was dealing with my fuel pump issue. So I know those are all good.

Remember that in my last post, I noted that when the hazard switch is turned on, all exterior lights flash. This means it is not a case of corroded bulb harnesses or bulb ground wires.

The turn signal switch on the column has no effect when moved up or down when the car is idling.

Both the hazard making all lights on and the directional not lighting them at all would make me think each are attributed to bad flashers... but how likely is it that BOTH flashers have gone just from sitting?

I could not find a group of grounds under the hood near the fuse block. I did notice, however, that the top fuse only has one wire on the left and the second from top fuse only has two wires on the right. Seems odd to me that there aren't wires on both sides of those fuses.

I agree that we can tackle the tach and wiper issue after we get the turn signals sorted out.

It's too dark out now for me to reseat the flashers, I'll try to do that in the morning. Feel free to post more advice.
Jeff Grant


Jeff,

guess the hot weather and lawn mowing took its toll ... last post was a bit off kilter <grin>. A big glass of iced tea followed by a chocolate shake and I am cool again. This long post - probably too much info.

As to your fuse box question .... pull up the wiring diagram for your car and follow along:

The top 2 fuse connectors are bridged together on the left side. The single Red/Green wire plugs in on the left side of the top fuse (position 1) and is internally bridged to the left side of the 2nd fuse (position 3).

On the right side of the top fuse (position 2), a pair of red wires connect. These should be connected to the running lights on the left side of the car.

On the right side of the 2nd fuse from the top (position 4), the other pair of red wires connect. These should be connected to the running lights on the right side of the car.

Continuing on down, the 3rd fuse receives its power from the ignition relay on position 5 on the left. On the right at position 6, all of the Green wire circuits connect (key on stuff - heater fan, wipers, etc.).

The 4th fuse receives its power from a Brown wire coming up from the starter solenoid on position 7 and on the right side at position 8, all of the Purple wire circuits connect (key off stuff - boot light, cigar lighter, etc.).

Under the hood somewhere towards the front of the car and usually near the fuse box you will find a gang of black wires. Find those and be sure they are well grounded.

As far as both flashers going bad after setting up .... I would say it is possible - especially if any moisture got into them and the contacts rusted together after 7 years of non-use. Remember, they are electromechanical and use a metal strip wrapped with a wire to heat the strip causing it to bend which in turn opens the contacts. Then, when the wire cools, it flexs the other way and the contacts come back together. It does not take much corrosion to stop that process. A generic replacement would be: Buss 550 flasher.

Since the emergency flashers are working, that lets us know you have good sockets and bulbs and some grounds.

Again looking at the wiring diagram, note that the turn signal flasher is powered via a green wire from the emergency flasher switch and the emergency flasher is powered by a brown wire. Locate the green wire on the switch going to the turn signal flasher and verify you have 12v when the ignition key is in the on position. Then, verify you have 12v at the green wire going into the turn signal flasher.

At this point, if you have 12v at the TS flasher, then lets check the output of the TS flasher. If you have a meter, connect red lead to the flasher and ground the black led. You should see meter alternate between 0 and battery voltage. Optionally, you could hook up a test light at the same spot and watch it flash on and off.

If you got a no voltage out of the TS flasher, time to replace it. If you have voltage, we know the problem lies downstream of the flasher ... the next check would be at the TS switch on the column and verify you have alternating voltage from 12v to 0v on the Light Green / Brown wire at the TS switch.

If you do, then flip the switch to turn on the right turn signal(green/white wire) and verify that you have alternating voltage on the GW wire. Repeat for the left signal (green/red wire). If no voltage, then it is the switch. Otherwise, the problem is downstream of the switch. I have not looked at a TS switch up close in about 10 years so I don't know if it is a repairable thing or not.

If the problem is downstream, then it will be time to check for shorts and continuity between the switch and the sockets to see what turns up.

The fingers are tired now ... I check in tomorrow on you.


Pat Harrison

Update with some progress this time!

I took down the dash behind the glove box and found the flashers. The hazard one had already been replaced as there's a round can with those wires going to it. The directionals were still attached to a stock looking blinker module.

I swapped the plugs from the directional one to the hazard one, and the hazards came to life!.. first slowly, then quickly as I'd remembered they were unusually quick in the past. I put them back, and my directionals still did not work.

I think I'm going to replace them both to be on the safe side as they're not expensive.

While I was in there, I confirmed voltage from the directionals and found about 10V on the solid green wire no matter which way I had the signal arm turned but I got a full 12V with the hazards on. I suspect this is alright since I didn't have the car running when I checked the turns and the fuel pump was running. I'll know better once I get the new blinker modules and attach them with the car idling.
Jeff Grant

I started a new thread regarding my wiper issue... It's entitled "80 LE wipers won't work"
Jeff Grant

10v on a green isn't right. You have to differentiate between the green running from the hazard switch to the turn flasher, and all other greens.

The first should be 12v with the ignition on and the hazards off, and zero volts with the ignition and hazards on and the turn switch off. With the turn switch on you should get 12v flashing on and off with the hazards.

All other greens should be 12v all the time the ignition is on.

Hazard and turn flashers are very different, you must get the right one in the right place. Hazard flashers are designed to flash anything from 1 to 4 bulbs and on a wide range of voltages, at more or less a constant rate. Turn flashers are designed to flash just two bulbs plus the tell-tale, if the voltage drops even a bit they start to slow down, and if one bulb fails they stop flashing altogether which is designed to alert the driver. Put a turn flasher in place of a hazard flasher and it will burn out, the other way round is dangerous as there is no bulb failure indication. A hazard flasher takes a second or two to 'warm up' when first switched on, then starts flashing on-off-on-off. A turn flasher powers the bulbs instantly, then after a second or two starts flashing off-on-off-on.
Paul Hunt

This thread was discussed between 14/06/2008 and 17/06/2008

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