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MG MGB Technical - A close call

I very narrowly avoided my car going on fire today. On the way home from work, the inside of the car suddenly filled with smoke. It was coming from the back. I immediately turned off the engine and coasted to the side of the road. I pulled out the back seat to see if it was the battery. It had the smell of burning wiring. It wasnt but luckily what was burning had stopped when I turned off the engine, so I tracked the problem down to the fuel pump. What had happened was the jack had slid forward and connected with the exposed positive terminal on the fuel pump, grounding it out and causing a short. And sure enough the feckin' thing isnt fused so I ended up with a couple of burnt wires. I caught it in time though so there was no major damage done. I rectified the problem in about 15 minutes. Whats that blue thing with the wire going into it attached to the bulkhead though? The wire to it comes from the same positive terminal as the pump. The pump works without it though cause I had to bodge the wires to get me home so I could repair them properly and I didnt reconnect this doohicky.

Anyway, next time Im tickering with the car Ill put a fuse in that circuit. Paul told me all about it and sure enough told me to check and I didnt. Silly me. Its amazing how easily these things can happen though. Anyway the terminal is insulated properly now.
Ross Kelly

Well, Ross, if it wasn't for bad luck, you wouldn't have any luck at all.

Your fuel pump is located where it can contact the jack? Isn't your pump located under the car away from stuff in the trunk?

Charley
C R Huff

Ross - Paul Hunt has advocated an in line fuse for the fuel pumps ever since I can remember. A 10 amp fuse in line with the fuel pump /would be a very wise addition to all MGBs. The other thing you need to do is get a replacement cover for your fuel pump where it sticks into the trunk so jacks and other brute force instruments don't come in contact with it. You had a relatively easy problem to fix, imagine what would have happened if the jack had hit with more force, like when you were forced to make a panic stop, with all four wheels locked up and the jack had continued at full chat until stopping against the end cover of the fuel pump. A couple of burned wires would look like child's play compared to a pump with a smashed end cover, pedestal and points toggle. Cheers - Dave
David DuBois

Yeah youre both right. Im getting a bad run of luck. Ill get the fuse installed during next week. As for the pump cover, I didnt know there was supposed to be one. What is it, like a metal box that goes over it or something? Im sure I can make something up anyway.

The reason the jack hit it is because the back of the pump is in where the spare wheel lives and theres lots of space around the spare wheel so thats where I keep my tools. The jack is a fairly serious piece of kit. Its a 2.5 ton trolley jack. I have the pump protected temporarily now anyway. I insulated the terminals well and put some non metallic soft things between it and the jack and wedged the jack in place with the wheel.
Ross Kelly

Ross - Here is a picture (albeit somewhat out of focus)of the cover that goes over the end of pump to protect it.
Cheers - Dave

David DuBois

Ah ok. Yeah I dont have that. I must get one. What is the blue thing for? Is it a ballast or something?
Ross Kelly

Ross,

the blue bit is a capacitor. Don't worry about it, you do not really need it.
The black shield was std. factory equiptment for 1974 1/2 on cars and must be fitted with the pump in this location!

Ralph
Ralph

Ross. I would not become too discouraged about your "run of bad luck". It is "bad luck" only because you are new to these cars and are still in the learning process. To those of us who have been doing it for a while it is "the normal de-bugging process" associated with the purchase of any older automobile. I find that it takes some period of time, with any newly purchased older car, to go through it and find all of the little "field expedient repairs" made by previous owners, then to correct such repairs. In the process, you learn a great deal about your car and realize why it is better to take a little extra time and fix the problems correctly the first time.

Your attitude is good, you are developing the basic mechanical skills necessary, and you have an excellent support group in your efforts. When the car is fully de-bugged, and this can take a year or more, you will have a car that is as reliable as a modern car and much easier for the owner to work on than a modern car. Most of us have been though this learning process. Most of us are still enjoying doing it. And, most of us did not have access to the level of support that you do today. You will do fine.

Les
Les Bengtson

Definitely fit a fuse in the pump circuit - both my MGBs came to mine with burned pump wiring. This should be fitted as close to the supply as possible, not the pump as one might think as the fuse is to protect the wiring and not the pump itself. A very convenient position is where the rear harness joins the main harness in the mass of connectors by the fusebox. Get an inline fuse that takes standard tubular MGB fuses, put a couple of solder bullets (not the blue or red crimp type neither are the correct size), and with an additional single bullet connector you can insert the fuse between the two Harnesses.

I'd also recommend fusing the OD as the gear-lever switch in particular has been known to short out. For cars with the dash mounted switch get an inline as before but this time with male and female spades and the fuse can be mounted on the back of thge switch. For column OD switch models find where the yellow wire in the main harness joins the yellow or yellow red in the gearbox harness and insert a bulleted inline there. For UK gear-lever switches it is in the same place but where the white or white/brown from the main harness joins the white in the gearbox harness. For US gear-lever switches you can use one fuse to protect both circuits as both are powered through the inertia switch, so fit one where the whites come off that. You can still use two fuses if you wish, where the wire from the inertia switch splits off into the gearbox harness and rear harness.

Personally I'd use a standard 17 amp rated 35 amp blow fuse, I know neither the pump or the OD need a fuse as big as this, but as I say it is to protect the wiring and that size is perfectly adequate. It saves carrying multiple fuses around, and you should have two spare standard ones in the fusebox anyway.

And when you've done all that, I'd fit a battery cutoff switch as well, where it can be reached from the drivers seat. There are a number of other unfused wires that can short, it is a useful additional anti-theft measure, and especially if you have an alarm or other stuff that puts a permament load on the battery (even the alternator does this) saves the battery getting partially discharged if only used periodically. Remember shorts can happen when the car is parked almost as easily as when it is being driven, I'd hate to have either of my cars burning away merrily and taking the house with it.
Paul Hunt2

BTW, a clearer photo of the cover attached.

Paul Hunt2

Paul, I was sure you would recommend the capacitor to protect the points from spark pitting. Do you agree with Ralph that it is not needed?
Fred Doyen

All pumps *should* come with the requisite capacitor or diode internally to protect the points. The external capacitor that is often present, usually blue as Ralph says, is a noise suppression capacitor and doesn't affect the points. Some markets mandated these in various places on the car (like the coil and voltage stabiliser) to prevent electrical interference to *other* cars equipment, my V8 doesn't have any and there is no radio interference - that I can hear over the wind noise :o)
Paul Hunt2

This thread was discussed between 02/05/2008 and 12/05/2008

MG MGB Technical index

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