Marcos Maniacs

Dave and Larry,

For what it is worth, and my Marcos experience goes back a mere 42 years, many electrical issues with the Marcos can be traced back to poor ground connections.

Generally, if a bulb is working but not as it should (i.e is coming on when the switch command is for something else to come on or is not working at all, but is a good bulb, then that definitely points to a poor connection in the wiring and usually at a ground (black wire) connection. Bullet sleeve connections from one wire to another are notoriously unreliable when they get old especially once the corrosion has started between the inner metal sleeve and the bullet.

The ground is actually the negative terminal at the battery but obviously every single ground wire cannot be run back to the battery. Instead there are a variety of multiple ground wire connecting points. Any corrosion, mould, or moisture will soon interfere with the continuity and cause switches instruments and lights not to work as they should.

The Marcos needs warm dry weather low humidity and to be driven regularly. Clearly conditions that do not exist everywhere all the time. It is old technology and cheaply made stuff and is inherently unreliable once it starts to age and once people start changing stuff.

In time the wires harden and become brittle and not all connectors can be trusted to have been crimped and soldered properly especially not by a garage or home mechanic. Crimped connections work fine if done correctly and as long as they are not subject to stress like being pulled at.

The problems have a source and follow a logic.

A test bulb wire set (even just a home-made one – a bulb, two wires soldered to the bulb and with crocodile clips at each end is a cheap and fool proof test of whether there is a break in a line, so you can connect the battery direct to the unit that is malfunctioning.

If the test bulb rig passes current to the malfunctioning unit so that it works correctly you have an indication of where in the wiring the problem will be. Usually it is at a connection either at the malfunctioning light unit or close by for example at a connection.

If where the malfunctioning unit is happens also to be exposed to the weather such as at the headlights, side lights and indicators then the source of the problem is likely to be at the connections at the front end of the car which gets all the water and dampness.

Of course if a previous owner / mechanic fitted a non-logical wire set and assuming the person is not available to question, it may be necessary to go back to basics and start from there and by pass what-ever supplementary kit has been wired into the system.

It just takes time and patience.

Good Luck

Regards

David

Marcos 3L Volvo 3V-5890