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MG MGB Technical - Bizarre Electrical Problem

I am now beginning to understand all those Lucas jokes. It started about a week ago one fine evening. I stepped on the clutch and my headlights went out. Released the clutch and they came back on. Every time I stepped on the clutch they would go out again. (This made for an interesting trip home – every time I shifted gears my headlights flashed – I wonder what the guy in front of me thought).

As far as I know there is nothing electrical connected to the clutch (I have a 68 B with 4 synchro and overdrive). This odd behavior then spread to the brake pedal. Thinking I was now getting a clue I suspected that the brake light switch was somehow at fault but after disconnecting it there was no difference.

Some additional things that I noticed – when I step on the pedals and the headlights go out the left turn signal comes on steady (but faint), the front left sidelight goes out, and the high beam indicator glows (but no high beams of course). This behavior is the same on both high and low beams but was more consistent with the low beams. Today I lost the low beams altogether. Could it be the headlight switch?

The thing I don’t understand is why this was happening when I steped on the pedals. I’ve checked and there is no wiring anywhere near the pedals that could be being pulled or pinched. Does anyone have any ideas on where I should look to eradicate this problem?
Boris

OMG - I'm LOL here. Sorry, but this is the best laugh I've had in weeks! :-)

I guess being snowed in makes things that aren't funny (to some) hilarious (to others that it's not happening to).

Bizarre electrical problems are generally caused by a bad ground/earth somewhere. Have you said anything bad about your car in its hearing lately? LOL!
The Miz

Having owned MG's for 40 plus years I can empathize with your problem. Presently My 70 BGT is experiencing somewhat similar problems. I have narrowed it down to the fuse block. Sometimes my tail lights would work, sometimes one and not the other, then its neither or the instruments will not work.
Try moving the wires adjacent to the fuses, see if the problem could be there.
If all else fails, give it a good polish job, kiss it goodnight and it will have healed itself by tomorrow. But especially, never say an unkind word.
Lee Sheldon

Boris, the fuse box is directly in front of the pedal box (right-hand drive) isn't it? Could the pedal box be somehow coming loose and contacting the terminals on the fuse box when you press the pedals? I've never heard of this happening, but it's possible.

Have someone step on the pedal while you're outside the car (bonnet open) and see if anything rocks. If you do this at night (headlights on), you might even see a spark or two. Also look for burned or discolored wiring near the pedal box. This problem sounds like it could be high enough current to be quite hazardous. Remember, the headlight circuit is NOT fused, so an uncontrolled short will eventually cause burned wiring, and perhaps a more serious fire. So this is not a problem you can ignore.
Mark B.

I know you have said there are no wires near the pedals, but the clutch pedal is close to the dipper switch, or do you have yours on the steering column.

FWIW

cheers
Ian G Buckley

No, I haven’t said any unkind words to the car. In fact I too thought this was a pretty funny problem at first – but the novelty wore off rather quickly when a quick poke at the wires didn’t fix it. I guess I’ll have to check the whole circuit for bad connections. I’ve found an electrical diagram on the board at http://www.mgcars.org.uk/electrical/ (what a great resource!) and will attack the problem this weekend.

I’ve already removed the pedal box cover to see if by some strange history some wire ran through there – but it was all clear. The fuse box is well away from the pedals. The dipper switch is on the floor but that wiring looks good and does not route near the pedals. Good suggestion about having someone step on the pedals at night and seeing if there are any sparks or other clues that show up. This is one of the wife’s favorite tasks – sitting in the car in the cold, and in this case dark, garage while I give instructions on what to do (actually she is a good sport – helped me with setting the timing a couple of weeks ago).

I imagine that after going over the whole circuit it will get fixed mysteriously – but I’d really like to find what is causing this bizarre problem. I’ve been thinking of putting in a relay for the headlights for some time - even bought a relay last year but never got around to it. Seems like the time has come.
Boris

I once had a '48 Ford on which the headlights didn't work unless the driver's door was open. It's amazing what kind of odd problems bad grounds can cause...
Rob Edwards

Boris, How did you find that electrical site here on the MGCars website? It is not listed on the home page. How would anyone else have found it? It is great!! thanks for sharing.
Brian

I like resurrecting the Lucas trivia. What are the three positions on the headlight switch???? Give up ! OFF - DIM - FLICKER.
Douglas Martin

There is an obscure fault in which the heater cable becomes hot due to a ground somewhere else in the system. If the system grounds, there will be insufficient current left for the lights.

Using clutch/brakes might result in movement due to momentum. Have you looked near the clutch slave cylinder?

Pardon the ramdom thoughts, but then it's a random symptom.
Dan

Whilst we're on random thoughts here - Its not related to the altenator is it?

My thought process went along the lines of, what else do you do when hitting the clutch or brakes - well you take your foot off the accelorater. This slows the engine, which has an electrical connection through the altenator

Richard
Richard

Continuing on the theme of random thoughts, what about the major nexus of connectors on the starter lug. Down there, the + cable from the battery hooks into all of the rest of the circuits on the car. This came loose on me the other day, and caused a total electrical failure. When I was able to reach under the car and wiggle the battery cable, it was easy to diagnose.

Tighten the nut on the starter, and I was on my way. (For about a couple of miles, then I had to tighten it better). Be careful tightening this nut, as it is possible for the wrench to bridge to the solenoid contact, causing the starter to go. That could be dangerous when you are under the car, especially if it is in gear. Best to disconnect the battery when you tighten this. Not that I did it that way for my roadside quicky repairs.
Mark B.

THANK YOU BORIS!!!!!AFTER ALL THESE YEARS, I NEVER WAS AWARE OF THE SITE THAT YOU REFER TO FOR ELECTRICAL GUIDANCE. THIS SITE IS OUTSTANDING AND I HAVE E-MAILED RICK AND THANKED HIM FOR HIS TIME ON THESE ISSUES. NOT THAT LES / PAUL / BEN / STEVE ETC ARE NOT HEAVEN SENT ALSO, BUT THIS IS FAST AND EASY, EVERYONE SHOULD AT LEAST CHECK IT OUT.
STEVE C.
Steve C.

Boris, how did you get the lights to go out again, my wife could use a shift indicator light, and this one sounds like it may work. (lol)
Peter Humphrey

Boris,

I had a similar experience and finally tracked it down to a broken fuse, suggest changing all fuses.


Garreth
Garreth

My thanks also Boris...

What a fantastic site and once again, an endorsement of the value of this BBS.

Angus
AJ Munro

Nice.
Headlight switch gets my vote. As resistance at the contacts builds up so does heat, and the contacts melt their way into the plastic making it that much worse. Eventually intermittence and failure result. Pull the switch and have a good look at it. The rocker can be removed for close inspection. Any signs of heat are a bad omen.

Jim
Jim Blackwood

Headlights don't go through the fusebox so unlikely to be that. Did the panel lights fail too? If not unlikely to be the main lighting switch. If various lights glow dimly or go out when you step on the brake pedal that indicates (ho ho) a bad ground at the rear light clusters. These never had a wired ground but rely on the physical fixings, it isn't difficult to add a ground wire from one of these to the connectors in the loom. The heater cable heating up (how apt) occurs during cranking if the engine/ytransmission ground strap has failed. This shouldn't affect the lights which will still be powered from the battery even if said strap effectively disconnects the alt when the clutch is operated. Love to see how the clutch pedal is causing it, you need to get in there with a voltmeter and do some testing. You'll need two relays, one for each beam, and if you add fuses too you'll need one per filament i.e. four.
Paul Hunt

More electrical problems – this time my Broadband Internet was out (no, not while stepping on the clutch).

Regarding the electrical pages on the MGCars website, I don’t recall how I found it initially as it was some time ago. Knowing it was there somewhere I first went to the home page but I too could not find any link to it (this makes me wonder how many more interesting and useful “sub-pages” may be on the website but with no evident links from the main pages). A couple of months ago, while rebuilding my distributor, I did a Google search for “25D distributor” and the relevant page from the electrical section came up which I bookmarked, so I was able to find the electrical pages back from there.

Thanks to all for the suggestions. Problem occurs at idle too - foot off the accelerator. I did have one panel light (to the speedo) burn out – a coincidence? Engine ground strap is fine. After reading the information on relays I did realize I’d need more than one so this weekend I’ll be looking for bad connections / grounds.
Boris

This thread was discussed between 16/02/2003 and 22/02/2003

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