MGB & GT Forum

Hi all,

I have a 63 B with some PO wiring butchering. Behind the MG plate in the center console there is an 'always on' red wire (vs brown as I understand it should be) as well as a few green wires which flash with the indicators and so I am not confident of the wiring behind the dash.

I am looking to find an accessory wire/wire on with engine and was wondering can I tap into the wiper wire - these don't work with engine off so assume would fit the bill but wondered any negatives of doing this? Looking to add a 12v audio solution.

Failing that, what else can I tap into to run this?

Car has had earth switched.

Any help much appreciated.

LT

https://www.chicagolandmgclub.com/techtips/mgb/pdf/mgb_wd01.pdf

Why would you want to screw up the wiring even more than the PO? There should be a brown wire designated for the radio or worse case run a new line from the fuse box.

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1978 MGB
When diagnosing issues related to running and stalling, always check to see if you have gas in the tank first.

Glad you said it has had the earth switched as that would have been my first question if you are adding an audio system as it is sooo tricky isolating a negative earth stereo system in a positive earthed vehicle.

Looking at the wiring diagram for 1962 to 64 MGBs there is no first stop accessory position on the ignition switch (unless yours has been changed). It just has Off / Ignition on / Starter. So your options are either to use a permanent live or an ignition switched live. Your year of B is not particularly well blessed with fuse protection to the extent that several circuits run entirely unprotected; Fuel pump, ignition coil, overdrive (if fitted). The wipers, heater fan and indicators are protected, all running from the same fuse.

Personally I would pick up a new switched live feed from one of the white wires (switched but not fused) and introduce a separate in line fuse in that wire. . Rather than just cutting and joining into the wiring you could make this look like a factory installation by using bullet connectors which are cheap and easy to get hold of and the correct colour wire.

MG later introduced all manner of in line fuses over the years nearby to the under bonnet fuse box as more circuits were added, so this wont look wrong. For reasons best known to themselves they had still only doubled the size of the fixed fusebox from 2 up to 4 fuses by the time B production ended so having extra in line fuses was normal.

Isn't brown always on? I would like one which runs with engine, so don't risk flat battery?

Thanks for your reply - yes there is technically no accessory stop so should be clear it is to run when engine is on as I don't want to run down battery (or risk doing so).
When you say white wires such as unfused, could I run this direct from the one which is feeding into the wiper switch? Logistically that is close and I then I add a line in fuse to that?

Appreciate the insight,

LT

That should be fine.
I have a 63 B so yes, the wiper green wire is 12v power only when the ignition switch is in the Run position. This green wire is also one of several green wires that is fused at the fuse block in the engine compartment.

Edit: the green wire at the wiper motor is a female spade terminal so if you can fabricate a Y wire splice with 2 female spade emanating from a single male spade end, you can then branch off one of the 2 female ends to power the radio. This method will allow you to tap into the circuit without having to cut or modify the original wiring!


It’s good practice to use the inline fuse to the radio addition as you are planning!!





Edited 2 time(s). Last edit at 2024-04-16 07:00 AM by MG14611.

I'd be trying to find out why there's an always hot red wire, there shouldn't be one. Maybe wired wrong at the headlight switch?

That red wire just sounds like a PO addition. Most modern audio systems need a permanent, unswitched live as well as an ignition switched live. If you do re use it then its best to add an inline fuse.

Anything that can intro0duce better fuse protection the better. There were still some unprotected circuits even in the very last MGBs,

http://www.advanceautowire.com/mgb.pdf

Describe your intended components for us and tell us if you have an alternator or generator.
If you were planning to power an amp with an original generator you will run into problems.
If you do not understand relays this is the time to learn.
If the PO installed a relay under hood and had a switched white wire energize it and ran a red wire to the console I would have to give him a “ good on ya mate”.