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MG MGB Technical - Weird...

Ok While cleaning my trunk out on the B for its new liner to be sprayed in I found an aircraft toggle switch installed close to the front of the trunk. I went under the car to find out what it was connected to, and followed the wires to the pump and beyond that to the transmission OVD switch. Does anyone have a clue as to what in the heck this switch is supposed to do? I'd try flicking it but since the engines out it'd make it hard to figure out its purpose. I don't think its a fuel cut off switch from the way its connected to the pump, it doesn't seem to cut the power off to that, I can't figure this thing out and its been bothering the heck out of me!!!

CJ
CJD Dark

Sorry CJ it doesn't make sense.

The pump normally has a single wire (live) earthing thru chassis so if it is connected to the pump its taking power....
OVD switch is powered from column or gearlever switch also taking power from there.

If you give it power from the pump then your overdrive is permanently activated when the ignition switch is on.
That would be very dangerous I think

puzzled

Hi CJ.

It sounds like a one-off, possibly something to disable the car for security reasons, as you suspect.
It could be that it is arranged to blow a fuse if someone attempts to hot wire the car.
Do you have any extra fuses, maybe in a hidden location ?.

If you tell us exactly what it is connected to, I'm sure someone here will figure it out.

Don
Don

CJ
Is there another source of power to the pump? It could be the wiring harness to the pump caused problems and another electrical power source was used to power the pump. Or it could be the pump was rewired with a new circuit from the overdrive switch power source just to install a switched circuit. It does not sound like an elegant solution either way. The switch is almost certainly an anti-theft device. A concealed switch that disables the pump is a well established anti-theft measure. The car starts and goes a short distance on the fuel remaining in the carburetor and then quits.
Barry
Barry Parkinson

Are you sure it isn't cutting off power to the pump? Don't forget the engine will run for some time with the pump disabled. Does the car have OD? If not it is probably using the manual switch (if on the dash or column) as a crude anti-theft device ... but that would make two anti-theft switches which would be a bit silly. Which side of the OD switch is the aircraft switch wired to? If the OD side then Puzzled would be correct about it being dangerous, because if both the normal and the alternative power supplies were connected to the pump at the same time then the gearbox lockout switch would be bypassed and you would wreck the OD in reverse. But that would mean that the alternative power supply to the pump would only be available in an OD gear, which would be even sillier than having two anti-theft switches, so my guess is that it's wired to the 12v side of the switch and not the OD side (but there's no accounting for MG folk ...). If it is the later type with the manual switch on the gear lever then you have ignition voltage on the gearbox switch. I reckon whoever fitted it got so fed up chasing and not finding a problem in the main 12v supply to the pump that he wired in an alternative, via the aircraft switch, to use when the proper one failed.
Paul Hunt

CJ - I would have to agree that someone tried to set up a shut off switch to the fuel pump as a anti theft device. Problem is that, like so many people who try doing wiring mods to the cars are, in real life, lawyers, doctors, plumbers, any number of things, but do NOT have one bit of electrical expertise (99% of the problems with I have seen with Lucas electrics are the result of DPOs fussing with the wiring). Your best bet at this point is to forget about deciphering what the PO had in mind with this mod and rewire the pump the way it is supposed to be wired (stick a fuse in line with the pump while you are doin it). The pump should get it's power from the switched 12 volts, via a white wire from the fuse block (at least that is where it comes from on the 66 MGB). If you want to utalize the switch in the trunk, route the white wire through it. Good luck - Dave
David DuBois

I went through the wiring again with a circuit tester this time, powered the electrical system up and went hunting down the purpose of the switch. It's wiring is ghastly in a few ways. It doesn't shut off the pump at all, even trying the OVD switch did nothing. It wasn't until after I had gone through the OVD switchs' connections that I found what it was doing. Whatever the PO was thinking about when he did this might cost me a fortune to repair. It left the OVD engaged the whole time... I still can't figure out why it leads to the fuel pump still, I'm gonna rewire the electrics today and try not to go punch the PO's lights out. I'm just glad I found this out now rather then after getting the engine back in. Some security measure huh guys? Might cost me a few hundred to repair the OVD unit if it was damaged. I'll take it over to the jag shop later and let them check it out for me. Hopefully it wasn't damaged. Btw ya'll might find this interesting I found a radiator that'll fit into the B with no modifications, and 75 bucks less then a radiator from VB. It's new from a 49 ford pickup.
CJD Dark

I'd agree with the fuse, although it doesn't get it from the fuseblock itself but from a 4-way bullet connector en-route from the ignition switch to the fusebox. This is by the fusebox and where the main loom joins the rear loom, get an in-line fuse with short tails and bullets, and insert it where the two looms join. Likewise the OD where the yellow in the main loom joins the yellow/red in the gearbox loom ... although we don't know the year and there were variations in later models. Use standard 17 amp rated, 35 amp blow fuses as you have spares for those in the fusebox.
Paul Hunt

"Ok While cleaning my trunk out on the B for its new liner to be sprayed in I found an aircraft toggle switch installed close to the front of the trunk."

Easy answer... My car has exactly the same setup and is one of only a handful made under license by Cessna.
David

you mean someone actually installed this mess willingly and under license? Where is the person who did this and can I shoot him?
CJD Dark

CJD

"I found a radiator that'll fit into the B with no modifications, and 75 bucks less then a radiator from VB. It's new from a 49 ford pickup"

What differences are there? Number of rows? Tube and fin style? etc.

Thanks

Larry
Larry Hallanger

"one of only a handful made under license by Cessna"

Trying to cash in on the 'flying MGB' chucked out of the back of plane on a parachute?
Paul Hunt

"Easy answer... My car has exactly the same setup and is one of only a handful made under license by Cessna."

OK I'll admit that sometimes I'm slow, but you lost me on that one.
Bill Boorse

re:

Posted 21 January 2004 at 16:06:37 UK time
Paul Hunt, Solihull, UK, http://www.mgb-stuff.org.uk paul.hunt1@blueyonder.co.uk
"one of only a handful made under license by Cessna"

Trying to cash in on the 'flying MGB' chucked out of the back of plane on a parachute?

Posted 21 January 2004 at 17:23:01 UK time
Bill Boorse, Pennsylvania, USA, boris2@prodigy.net
"Easy answer... My car has exactly the same setup and is one of only a handful made under license by Cessna."

OK I'll admit that sometimes I'm slow, but you lost me on that one.

+++++++++++++++++++++++++++++++++++

This was a famous MG commercial back in the early '70s where and MGB was "launched" from a supply plane at altitude...with plans of a parachute opening, the plane slowing falling to earth, where is was driven off into the horizon by a happy MG driver.

Unfortunately, the first attempt resulted in failure, and the MGB landing on its bonnet and boot, pancaking it quite well!

This commercial sometimes appears as a vintage ad on Speed Channel...but not too frequently!

rick

rick ingram

Rick,
I've seen the commercial, I just didn't get (still don't) the connection to CJ's mystery switch. Busy day at work, I think part of my brain is shut off.
Bill
Bill Boorse

I assumed it was in some related to the "aircraft toggle switch"
Barry.
humor in writing is a different skill.
Barry Parkinson

This thread was discussed between 17/01/2004 and 21/01/2004

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