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MG MGB Technical - 1980 MGB problem

I have a few problems with my 1980 mgb that all happened at the same time.

Fuel gauge not working
Temperature gauge not working
Radiator fan not working
Brake lights not working
No nightime running lights on the fuel and temperature gauge

All other gauges and nightime running lights are working.

All fuses, wiring connections seem to be intact.

Any ideas?

Thank you.

Mark Denny
Mark Denny

There is a four way connector that is fed from the white/green fuse that may have become disconnected that would exp[lain fuel and temp gauges not working also the stoplights, Have you checked the fuse for continuity, it looks like you have a fuse problem as the green fuse feeds the Rad Fan Directly. Some times fuse look intact but may be broken at one end try swopping fuses for a known good one.
Have not figured panel light problem yet it may be bulbs,

Regards Patrick
P.T. Tighe

If one panel light works and the others don't then that part is probably bulbs.
The 'common' point for the rest seems to be White/Brown to terminal 5 on the fuse box. this is supplied via the ignition relay. If you have 12V there AND If the screen washer AND Reverse lights work then track down the 4way connector on the green wire from fuse block (6) (I guess somewhere near the fuse block/brake light switch). Fuel and Temp have a common feed via the voltage stabilizer also fuse block(6) but a different wire to reverse lights. The Radiator fan has an 'inline fuse' somewhere fed from that white/brown. I would check for 12V on all points on the ignition relay first. Sorry can't help with physical locations as mines a '70 and its all different :(
B Anderson

It's complicated by there being three separately fused green circuits on the 1980 UK model - one from the fusebox, and the other two from inline fuses just underneath it.

One of the in-lines feeds the cooling fan (fed by a white/brown from the ignition relay), the other feeds the heated rear window, indicators, heater fan and tach, but that comes off the white from the ignition switch to the relay even though it is white/brown at the fuse, and also feeds the ignition. Originally everything came off the relay, but they had problems with them sticking operated which left the ignition and fuel pump powered, so there was a mod that moved these back to the ignition switch for safety.

The fusebox green feeds the reversing lights, brake lights, washers, wipers, voltage stabiliser for the fuel and temp gauges, handbrake switch and seat-belt lamp, and is also fed by a white/brown off the relay. The relay also feeds the fuel pump, overdrive and ignition warning lamp directly.

Presumably the engine runs, and the ignition warning light works, so it can't be the relay itself. It also means that unless there are multiple faults it can't be a connector in the main green circuit.

However there are three white/browns at the fusebox and only two spades so two of the wires will be in one connector. It possible that one of those connectors isn't making a good connection to its spade, which means that two of the wires will be making a connection with each other, but not with the third white/brown. If the two in one connector are from the relay and to the ignition warning light and fuel pump, and the single white/brown is for the cooling fans, and it is the two in one connector that aren't making contact with the fusebox spade, then that single fault will affect the cooling fan via its in-line fuse, plus reversing lights, brake lights, washers, wipers, voltage stabiliser for the fuel and temp gauges, handbrake switch and seat-belt lamp via the fusebox fuse, but there will still be power for the fuel pump, overdrive and ignition warning light.

The two gauge lights not working are something else, probably bulbs or loose black connections on the back of the gauges, as the red/whites and blacks feeding them are from multi-way bonded connections and not bullet connectors.
PaulH Solihull

I had something similar just afew days ago. I checked the fuses for 12v each end, and that was ok. It was dirt and verdigre in the spade connectors. Being by the roadside, I cured it temporarily with an aerosol points cleaner.
c cummins

Mark: I too had very similar issues with my 1979 MGB. In the end, I diconnected the battery and pulled all the fuses from the fuse box and with my Dremel tool with the tapered end grinder:

Cleaned the entire contact surfaces in the fuse holders of the fuse box

Cleaned all the terminal ends of each fuse holder

Replaced all the terminal ends and fuses

Cleaned all the battery cable ends and battery terminals

That was 3-1/2 years ago and pretty much been electrical problem free.

These cars are over 30 years old and stuff like this will drive you nuts.

I was a very cheap repair and you have nothing to lose by trying it.

Let us know what happens


79 mgb
gary hansen

I have a similar problem with my '79. It can be traced to the wire between the fuse box and the ignition relay. I find the problem goes away by cleaning the connections.


This thread was discussed between 11/06/2012 and 22/06/2012

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