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MG MGB Technical - Brown ignition feed, HOT! Help!

I've checked the archives and perhaps I wasn't searching with the correct terms, but I couldn't find anything that addressed this particular issue.

The heavy brown wire under the dash that feeds the ignition switch has begun to get HOT. I found it as I reached for the hood release. It is extremely hot at the bullet connector where the ignition wires join the harness. With the ignition in the run position.

Of course it isn't warm with the ignition off. The brown wire still has juice with ign off.
So am I correct in assuming that I have a short somewhere either in the ignition switch itself, or in something immediately fed by the "ON" position, White circuit, feeding the green?

Could it be a bad ground at the switch?

If the green wire between fuse box and brake light switch (at the master cylinder) grounds, could it cause this hot brown condition? I thought I fixed it, maybe not.
T. D. Howard

TD - The brown wire getting hot is due to excessive current flow through it or else it is the result of a high resistance connection. I would bet on a high resistance at that bullet connection that you speak of. The wire doesn't get hot when the ignition is off, even though the wire still has voltage on it because there is no current flowing. I would suggest that you disconnect the battery and then take that bullet connector apart, clean it thoroughly and replace the female sleeve. I had one of these connections on our MGB lighting circuit get so hot from corrosion build up that it burned the wires several inches in each direction. When you put the cleaned connection back together, use some dielectric grease on it to keep the corrosion at bay.
Good luck - Dave
David DuBois

I had this very issue. The brown wire got hot enough to deform the insulation. It was due to most of the copper wires having broken at the connector David speaks of. I took the harness out and resoldered all of the connections. I never had another problem with it.
Matt Kulka

I have found that over many years, I would typically find 1-3 bad connector sleeves on a car. I have right now two, 74 midget and 73 B, on which nearly ALL the double connectors are broken, including the one mentioned, which was indeed HOT. Long term cracking is a common problem on hard temper brass. It is known to be age related, and appears to be heat related - on the B, I found 1 bad single sleeve, however, all but one double were broken. When I ran out of new ones, I dug into my good used supply - went through about 50 to find 5 good ones, and many of these were under dash and never wet or salt exposed. Evidently 30 years is the critical age for this failure.

Get new ones from http://www.britishwiring.com/ These are better than the originals and much cheaper than suppliers like big M. You need about 30 doubles and 30 singles (more on later cars) on a car - do them all. Use Oxgard on all these connections, and any others like spade connectors, bulb bases, batt terminals. It prevents future trouble, makes disassembly much easier, prevents corrosion. Get it at hardware/building/electrical supply stores.

FRM
http://www.usachoice.net/gofanu
FR Millmore

Thanks fellows,
Well I did some wire crawling yesterday evening and, whaddayaknow, we were all right.

The brown connector was, indeed somewhat corroded. This is where, when it rains, the water chooses to travel. So I dismantled the dbl connector and cleaned it and the bullets. Put back together and still had the heating, to a lesser degree. but now white wires seem warm too, hmmm.
Walked around the car, noticed that the brake lights were on again. Got under the hood and on the ride home from work, the brake switch green wire had a bare spot that was grounding against the fuel line, YIKES. The subharness also showed signs of heating between the brake switch and fuse box. Upon further investigation, I pulled the switch itself and, as it broke into smithereens in my hand, noticed the spring and all contacts were grungy, and the plunger had no effect on it. BTW with the two brake switch wires disconnected the brown DOES NOT heat up.

SOOOO...my hypothesis is, the brake switch had stuck in the on position at some point, heated the sub harness enough to expose the wires of the green wire.
The exposed wires would ground themselves on the steel fuel line, and short the ignition circuit. because of the dirty corroded connection, the brown connector is where the heat built. I still don't know why the fuse didn't blow, but a 30 amp fuse is probably too big to protect a single 14 guage wire that has a dead short huh?

Anyway, spent the evening installing brand new brake switch wires between the main harness and switch, all nicely wrapped with new blue tape. The new Beck-Arnley stop-light switch from Advance Auto parts of all places will be here today. Keep your fingers crossed.


T. D. Howard

Firstly THANKS to all respondents. I've resolved my little issue.
My hypothesis was WAY OFF!
The dope that wired the rear harness (me, staring at ground, kicking small stones) made a wiring error. I plugged the right rear marker light ground wire, directly into the stop light connector with the wires that were supposed to be there.
I would never have discovered this but reading this board caused me to check that I had an engine ground strap. I discovered it was gone.
Upon replacing the engine ground strap,suddenly the alternator started doing it's job. Thats when the wires released copious amounts of smoke and much drippy insulation.
The brake wire WAS grounding against the fuel line, but it had never been hot enough to melt until I had current from the alternator. Melted wiring, the brake switch and vinyl wrap.

Funny, everything worked before, but the lights were dim, and the signals were very slow and the battery wouldn't hold a charge. Now with the ground strap back in place, everything works. All gauges, all lights, all signals. And they are bright enough to be seen.

Now after two years I can finally say that as of yesterday afternoon my 73 MGB has no electrical issues.

Lets see how long that lasts.
TDHoward

I don't wish to turn this thread into 'Bullet Bores' but... I kept losing power to the indicators/fuel pump/instruments. A fiddle at the fuse holder would get them all on again but there was no apparent problem with the fuse. Then an accidental fiddle of the bunch of connectors near the fuse holder revealed an erratic supply to the white wires and on inpecting the bullet connector it disintegrated. With a new connection made I was dismayed to find I still had an erratic connection at the fuse. Moving one end of the fuse connector restored power so I cleaned it and voila, end of problem. Two bad connections on the same line - not fair! Ok, you can all wake up now...
PK Flush

TD. Not to upset you or anything, but...
You must have been making a circuit somehow with a ground for the engine through something for the ignition to work. You should look for the poor unfortunate cable that was the ersatz ground... before it fails on you too.
Choke cable is most common, could be throttle cable too or something else I'm not thinking of (duh ;).
Whatever it turns out to be, it will have lots of nasty little burns on it from the arcing. If it was the throttle cable, you may need to regrease your pivot bush.

Mike!
mike!

TD - One more item that may rain on your parade. Keep a close eye on the brake lights since the replacement brake light switches, regardless of where they come from have a tendancy to be outright whimpy and will often burn out within as little as two weeks. I went through close to half dozen of the things before finally throwing in the towel and adding a relay and arc suppression circuit to the brake light circuit. That has ended my problems. If you find that the switches are not holding up for you, see my article on the brake light switch relay and arc suppression circuit and the instructions for making and installing it at: http://www.omgtr.ca/technical/brakelightrelay/brakelightrelay.htm
Good luck - Dave
David DuBois

Thanks for the heads up fellers.
I think (there I go working without tools again)
that the (weak)ground may have been accomplished by the steel oil gauge line, and possibly a PO installed stainless wrapped hose, The choke cable has been removed so it needs replacing anyway, upon inspection of the throttle cable it seems fine, recently lubed and working well. If it were something else I'm sure it'll make itself apparent one day when I least expect it.

The brake lamp switch is Beck-Arnley distributed and it actually says LUCAS ENGLAND on the body of the switch. It appears identical to the old one.
I will watch it though, and hang onto the receipt, it has a year warranty through the parts store.

Of Course, I spoke too soon concerning the lack of electrical problems, seems that the reverse lights come on in every gear. Another trip to the archives;-)

TDHoward

What do you mean "come on in every gear" ?

Do they just come on when you switch the ignition on ?
Iain MacKintosh

No I mean they are off when the car is in neutral.
They light not only in reverse, but in all four gears. Always off in neutral, but on in any gear. From the archives I deduce that the switch at the top of the tranny must be shimmed to achieve the correct distance to work only in reverse. I figure the switch is working since they are not on all the time.

I also understand that this is not a fun job.
TDHoward

This thread was discussed between 28/07/2004 and 03/08/2004

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