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MG MGB Technical - Wiring in Factory Radio (BL/Bendix)

Hello,

I have a factory British Leyland / Bendix model radio (1975 model) that I'm trying to wire into my car. The unit is a stereo model, with a four prong plug for the two speakers. The speaker plug is straight forward, a +/- wire for each speaker. My question is there is also a black wire (fused) and a red wire coming out of the back of the radio. Is the black wire the ground and the red wire the power (ignition)? The case also has a lug for mounting/grounding. I would think its a negative ground radio, as its dated 1975. But the fuse on the black wire is throwing me off. Does anyone know how to wire this particular radio to the car? OR Does anyone have this radio on their MGB that could tell me how its hooked up for power?

Thanks.
Ron Koenig

The fuse in black might imply a +ve earth radio. that is assuming that convention has been followed and red is 'Live' e.g. +ve. The red would therefore be Earth. Radios are not normally earthed through the case. May be worth taking the case off and see where thing go inside.
B Anderson

Picture

Ron Koenig

Yeah, I took the case off before posting on here. It appears that neither wire grounded to the case. They are soldered directly to the circuit board.

If I assume this is a positive ground radio, they I would definately not want to ground the case to my negative ground car. Would simply reversing wiring +/- work?
Ron Koenig

The fused line might possibly be for a powered aerial, so ground is through the case?
Pat Gregory

It does sound like a positive earth radio given the fuse in the black i.e. -ve supply. Radios usually do have a supply fuse, and that would protect anything the radio was supplying i.e. an electric aerial. It would be illogical to fuse that, and not the radio, but anything is possible.

The red could be night-time illumination, that is the colour of parking/running light wiring of the era.

Electronics don't usually like reversed polarity. You *could* try connecting -12v to the black, and +ve to the case, i.e. two wires from a battery to the radio, with the radio case not touching the car body and see if anything happens like a panel light or hissing from a speaker. Use just a length of wire as an aerial, don't plug any aerial that you have on the car into the aerial socket on the radio.
PaulH Solihull

This thread was discussed between 25/05/2012 and 28/05/2012

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