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MG MGB Technical - 1979 MGB gauges and brake lights do not work

I have a 1979 MGB I was hit on the passenger side fender and door. I am trying to fix it on my own. I have found that since the wreck the brake lights, temp., fuel, gauges and the tachometer have stopped working. I checked the fuses and they seem to be fine. I need help figuring this mess out if anyone can.

Daniel. The circuits you mention are controlled by the third fuse down. Check, using either a test light or a volt meter, for power into the fuse (front side) and power through the fuse (back side). If you have good power through the fuse, check for power going to each of the wires on the back side of the fuse. If you show good there, you need to get a copy of the wiring diagram and start tracing the circuit to find out where the loss of power occurs. Les
Les Bengtson

While you are at the fuse block. You might want to remove all the fuses and wires (remembering where they all connect back to)then unscrew the fuse block from the car check for corrosion especially on the back side, and clean it up thoroghly using a small wire brush. Corrosion at the rear has been known to cause some of us troubles in the past.
John '79 MGB
John F

A simple and safe way to clean the fuse block is to:

1) remove from car AFTER writing down the location of
each wire. (Paper remembers, people forget!)

2) Immerse fuse block into a container of Muriatic

3) Rinse with distilled water after removing from
Muriatic Acid, allow to dry.

4) Installation is reverse of disassembly.

5) Use dielectric grease on all connections.


rick ingram

How badly was it punched? I'm leaning more toward impact damage than corrosion, although the latter may certainly be a contributing factor. The wiring harness passes through the firewall at the top right corner near the windshield post (near where it sounds like you were hit). I'd be inclined to check there for damage to the harness.

Rob Edwards

There is also the inertia switch that can trip in a smash isn't there? It is up behind the dash somewhere and from memory is a small white cylinder with a button on one end to reset it? I have no idea what it switches though (fuel pump perhaps). I am removing it from my roadster since I am redoing the wiring.
Simon Jansen


Inertia switch should be in the fuel pump power lead. I am in the process of adding them to my A and C. Don't want to burn if an accident breaks a fuel line and the pump keeps on pumping.


Larry Hallanger

I went to a salvage yard and got a fuel pump inertia switch from a Ford Tempo to install in my 74 B. Cost $5, the one I have was made in the UK.

Clifton Gordon

This thread was discussed between 14/03/2005 and 16/03/2005

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