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MG MGB Technical - pump cutout

hi all
i have a spare switch on my dash. if i cut into the live feed to the pump near the fusebox and connect to spare fog light switch can you see any problems with doing this.
thanks bob 1970 bgt.
Bob Taylor

No problems at all. You just have to remember to always turn the switch to the on position. I speak from embarrassing experience. RAY
rjm RAY

Bob i have sent you an Email about this, A.T
andy tilney

cheers andy thanks very much.
bob
Bob Taylor

On my old GT I used a DPDT switch and wired it into the pump and fuel gauge. With the switch off no pump and the gauge would just read empty. That would remind me to switch it on after getting in the car and checking the dials over.
Simon Jansen

Remember it is unfused, so it would be wise to fit an in-line between the whites in the main harness before it goes off to your switch. Both my cars and a couple of others I have worked on have all had shorts either in the pump or on that wire in the boot even with factory wiring. Remember also to make good connections!
Paul Hunt 2010

A very good suggestion. This is what I did when I ran a switch for my fuel pump. I also installed one for the overdrive and another for the reverse light circuit. RAY
rjm RAY

I've also fitted (and recommend) one for the overdrive, but the reverse light circuit is already fused.
Paul Hunt 2010

The reason I put a fuse in my reverse circuit was because my car is a '67 and only has 2 fuses. The reverse light wire had chafed on the crossmember and when reverse was selected, it would cause a direct short and blow one of the 2 fuses. I figured that a separate fuse, just for the reverse lights, was a good idea after I discovered the bare wire. RAY
rjm RAY

Doesn't matter whether it is a 2-fuse or 4-fuse car, chafed wires on a circuit fed by the green fuse will blow it. You could say that fusing *every* circuit separately is a good idea, since not only does that avoid losing all the green-powered circuits in one go but it also helps you diagnose where a short has occured. It's one of the reasons why modern cars do usually do fuse most things separately.
Paul Hunt 2010

When you put the extra fuses in the fuel pump and OD circuits do you change the wires down stream of the fuse to a colour that indicates it is a fused wire. White would change to purple. I have found that an understanding od the colour convention makes fault tracing easier.
David Witham

I've split the wires that come out of the fuse box and installed several fuses going to each circuit. This way, I can reverse the procedure and return the wiring harness to stock if need be. RAY
rjm RAY

White would change to green, as both are ignition powered, the first unfused and the second fused. Purple is always on fused so not appropriate for either, particularly the fuel pump. You would have to make up your own gearbox and rear harnesses to change the colours, certainly not contemplated by me! One of the reasons for placing the fuses where there are connectors is that they should be easily found and obvious by anyone else ... but hopefully not until I have turned up my toes and the cars are sold on. After which I won't really mind what happens. Another reason is that they can be unplugged and the wiring returned to standard, should anyone (else) wish to.
Paul Hunt 2010

Paul, white to green is correct. A slip of the old brain writing purple.
David Witham

This thread was discussed between 12/06/2010 and 18/06/2010

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