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MG MGB Technical - Meltdown and harness question

Well, we almost lost her yesterday. Just finished the winter work on the wife's beloved '77B - Fix Cracks-o-Doom, causing attempts to blend paint to eventually cover entire car, Door adjustments, plus add new retractable antennae, headlight rims. new battery, etc. First nice day that the wife had time to herself, she was ready to roll. Fired the B up and bachet it onto the driveway for final cleaup, I had to go out of town for the day, but before I left, she insisted I go with her for a short check-out ride. Smart move. About a quarter mile up the road the smoke started to hit us. Reflex reacted before reason and I immediately had her shut down and pop the hood. The engine compartment was clear. At the same time she yelled that the smoke was still coming from inside the car. I ran over and realized that she had not turned the key all the way off. I turned it off and things finally settled down. The good news, no flames, and we were able to coast home all the way into the garage. The bad news a number of wires were toasted near the steering column on both sides of the 7 pin connector. Lots of metal strands showing. One was just strands all the way into the harness. That is all I know as of last night's quick look.

I disconnected the battery and left it to ponder the situation. Obviously, I have to do a post-mortem to figure out what started it. I do believe that the heater blower started running during the incident, but the switch was and is off. Not sure what else was effected yet. My thoughts so far is that it would be smart to replace the dash wiring harness. I saw this morning that Vicky-Brit has them available. I'm not sure yet which side of the connector it is that took the most damage. I do find it curious that there is descrete damage on both sides with no apparent damage at the connector itself. It just might be able to take more abuse before showing effects.

Looking for any advise as to the best way to go about investigating and determinig the culprit. Also, how hard is it to replace the Dash harness without taking the dash out? I should have little problem identifying the wires as I have the diagram, and another '77B project car in the driveway with the dash harness in tact.

And the wife was so happy to get back into her baby too.

Any thoughts or advise besides the obvious - carry a fire extinguisher - would be appreciated.

Thanks,
Mark R.
Mark Rotsky

Sure sounds (and smells) like high resistance in the bullet connectors generating a lot of heat. A little silicon dielectric compound on reassembly would sure help. Wish they had that stuff back in the 60's!
tom

Mark, first you have to find out which wire started the heat. Strip back the tape on the harness until you can find the color code of the worst wire, or at least until you can eliminate all the others. It's probably on an unfused circut. What you want to eventually find is the cause of the overload, before you repair the harness or replace it. I've seen an unused ignition ballest circuit cause similar problems after a DPO installed a new electronic ignition.
Bill Young

I found the culpret. It was the white/green radio hot wire. Melted all the insulation off from the ignition switch right to where it was grounding itself to the radio chassis. Of course that's right before the radio's in line fuse. I had it installed 4 years ago by Circuit City. I guess when I replaced the antennae, I must have moved it a bit, and then when we took that ride, we made a left, then right turn, and that disturbed it enough to make contact. The main harness looks like a limb with a knife gash all along it, and bare wire strands laying inside the wound. Even the main ignition harness from the key switch looks like that. The only way I could figure out which wire it is was by elimination and proximity. Then I recognised the melted white and green plastic along the other wires. All other wires along it as it ran are glued together from it's melted insulation. I've started cutting away the harness wrap and separating them all. I've actually been successful with this as I've un-glued and separated all the wires around the connectors, and I'm just staring to evaluate the collateral damage. Not pretty. I think I can shorten or replace the problem wires around the connectors as the harness carrying the radio wire is long here. My biggest concern is the wiring up high behind the dash where I'm still opening it up. The individual wires appear to be intact, but I need to really get in there to make sure. I also don't know what shape the inside of the ignition switch is in.

As I stated before, Vicky Brit has a Dash Harness that shows a connector to the main harness at the right side of the dash. But my harness doesn't have a connector there. It just continues through the fire wall and right up to the headlights. Too bad. If it was able to be disconnected easily, I'd buy a new one without question. Now I'm going to take the time to try and repair the mess. Then I'll have to test every circuit and component that might have been effected

Any other suggestions would be appreciated.
Mark R.
Mark Rotsky

Mark,

The multi-connector that connects the dash sub-loom to the main loom should be there. I can't imagine a DPO taking the time or effort to hard-wire all of the circuits direct to the fuse box. It may be tucked into the wing void space on the passenger side. To answer one of your questions above, I'd take the dash out. It makes working on the harness so much easier. Also, taking the seats out helps with access, just remember to keep track of the spacers under the rails.

Doug
D. Cook

Doug,
I would be thrilled to find the connector hidden in there. Do you know exactly where it might be relative to the firewall, dash, or anything else? I've felt along the harness and haven't found any evidence of a connector, but I didn't realy expect to find it UNDER the wrapping. Again, it's a '77.

I have the steering wheel and cowl off, glove box out, consoles loose, and seats back and lowered. With this I have resonable access so far with my back on the floor, but haven't gotten way up behind the vents yet. I've never taken one of these dashes out before. Maybe now's the time to start.

Mark R.
Mark Rotsky

Mark,

By removing the steering wheel you've gotten the hardest part done in taking the dash out. All thats left are the four or five 7/16 nuts on studs way up in the dark past all the wires. Once its out of the way you should be able to find the connector. My car is also a '77. Rats eat my wiring while I had the car stored so I have done a harness rebuild myself. Another suggestion is to print-out the wiring diagrams on this site and note exactly which wires are connected to which terminals on the voltage stabilizers. A picture could be worth a thousand notes.

Doug
D. Cook

I have been contemplating changing out my main harness and have looked to see where it connects to the dash harness. Like Mark, I can't find the connector either. I would also be curious as to where under the dash the two connect.

Jayme
77MGB
Jayme

Jayme,

I just went out to the parking lot to look at my car. I removed the oval grommet behind the charcoal canister to see if I could see the connector and it was not in sight. But, as I mentioned above, I rebuilt mine and now I recall that I moved the connector further inboard. Originally the connector was behind the round grommet in the wing.

Doug
D. Cook

If I understand you correctly, you access it from under the hood and not under the dash? I will look again. Thanks.

Jayme
Jayme

I don't know about you, Jayme, but I found no evidence of a connector in my harness on either side of the firewall.

But the good news is that it looks like the radio power wire that melted down didn't appear to have that bad an effect in the middle of it's length, up high behind the dash. It actually has the insulation still on it in that area. Does that make sense that it would get hotter and cause more damage at the ends? Anyway, I separated all the wires that were next to the meltdown along most of the length, and except for the real bad area by the connector to the ignition switch harness, the rest of the wires appear to be intact. Ugly, but intact.

I think my next move is to pull all the contacts from the main connector where it mates to the ignition switch harness, and cut away the ends as that's where the most damage is and I have the extra length to spare. Then I'll re-connect the contacts to the wires and reload them into the connector shell. Then I have to replace the white/green radio lead from the ignition switch all the way through to the radio. I also have to replace the brown between the same connector and the light switch harness. I think that should do it, as long as I didn't miss any other damage and the ignition switch isn't damaged inside. That white/green cooked right up to the switch. Will have to do a slow, gradual power up before leaving the garage again. Not as clean as a new harness, but a fire extinguisher will be in the car, and we will start off slowly.

If this works, I consider myself lucky.
Mark Rotsky

The dash harness and plug shouldn't be an issue as the white/green doesn't go through it. Where provided this is high up at the back of the dash, on a UK model (with two connectors) you have to dismount the dash and pull it forward before you can see and unplug these. The same fault current would have been flowing through the brown from the light-switch to the double-brown connector somewhere near the firewall as well as between the ignition switch and the light switch. If only the latter has been damaged, either you were lucky or the former is a heavier gauge. The switch itself will now be suspect, possibly being high-resistance and dropping some voltage under high load conditions, you could do some tests. What also may have happened is that any heat being developed inside the switch may have caused some loss of springiness of the contacts, which may mean intermittent or bad connections down the road.
Paul Hunt

Hi Paul,
Its been a while.

You are correct in that the other critically effected wire was the brown between the double brown connector and the larger main connector where it resides right next to the white/green. In fact, there's no brown left to it at all. Amasingly, the brown on the other side of the double brown connector to the light switch, and the other wire of the double brown were not effected. The brown from the main connector to the ignition switch looked "stressed" at the ends, but not really melted at any point.

I agree with your comments for concern about the ignition switch itself. Can you suggest specific tests w/readings that I could take to help evaluate its status?

Also, what are your thoughts as to the condition of the wires that were adjacent to the white/green? They seem to be intact and covered. Would you trust them? My concern is with their insulation. I believe they are good as far as making complete contact with their intended components, as even the strands of the white/green were still attached well.

Thanks,
Mark R.
Mark Rotsky

Mark,

I also have a 77B. There is a dash subharness connector in there. I replaced my dash harness with the dash in situ, just took out all the gauges. I also agree with Paul H that the ignition switch may heve been damaged and will undo all your good work if not replaced. If it were my car, I would buy the dash subharness and replace. I'm not a fan of Victoria British, my recommendation would be to get a dash subharness from British Wiring http://www.britishwiring.com Nice people and good products.



Paul K

Thanks Paul,
Interesting site. I'll have to dig into that further.

I got the car running yesterday. The white/green and the white/red wires coming out of the ignition switch are dead. I had to rewire the radio through the white ignition lead. Seemed to work fine. I also spliced in an extra fuse. Just in case.

All components and lights worked fine, so we started her up for a nice test ride. But the weirdest thing happened. The first time we started her up, the fuel pump failed to work. With all my wire testing leading up to the startup, the pump always clicked away as expected. I double checked the wires under the dash (Obvious starting point), but all looked OK. I traced all the way back to the pump and was getting power and a ground. For lack of a better idea, I pumped the fuel regulator and got enough fuel to fire the engine, but it then died. I pumped the regulator again, and all of a sudden I heard the pump come back to life. Just like that it healed. The wife took it to the local car wash for a good vacuuming (cell phone in hand) and had no problems. Has this happened to anyone else?
Thanks,
Mark R.
Mark Rotsky

Mark,

Do you still need a dash sub-harness and ignition switch? I found a 78 B in the boneyard today, and took those parts out. You can have them for the cost of shipping.


Paul K

Paul,
Yes, that would be great. I had to circumvent two leads on the ignition switch because they had died during the incident which leaves the rest of it suspect. And having another sub-harness at the ready wouldn't be a bad idea either. Please email me at Mark_Rotsky@Raytheon.com and we'll discuss the details.

Thanks for thinking of me.
Mark R.
Mark Rotsky

Mark, I'll send an Email to that address. Gotta look out for my fellow BoSox and MG fans!


Paul K

This thread was discussed between 28/03/2005 and 12/04/2005

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