Download Electrical Fault Finding on an Alfa Romeo 90

Electrical Fault Finding on an Alfa Romeo 90
You will find most of your electrical faults on any car are going to be caused by two things:
Poor conductivity through a connector with dirty / oily / oxidised (rusty) contacts,
Bent / broken pins / sockets, or
Through bad / improper earths.
For this discussion I will assume that you have limited or no electrical ability or knowledge, so
please don’t be offended by any oversimplified explanations. Conventional current flow is
assumed throughout this explanation (ie. + to ) as opposed to electron current flow.
Electricity is dumb and lazy, and it will find the easiest (path of lowest resistance) way to get
from your positive battery terminal to your negative battery terminal. If you have a high resistance
joint, it will find another path, burn out the joint or simply do nothing at all.
The first step in finding these faults is to trace the wiring system from the battery all the way
through to the power consuming item. Make a drawing of what you traced and label anything you
pull apart (so you can put it back together again). It’s usually easier to stars from the end point
and work back to the battery. If you have a multimeter, or voltage test probes, it will make life
easier. Don’t assume any wiring diagram is accurate. I have seen, numerous times, people pulling
their hair out because they couldn’t match the actual circuit to the diagram and therefore find a
fault. Quite often wire colour codes are wrong, relays and fuses don’t exist or someone may have
modified something.
Second step is to check every connection. Start with the earth point from the item to the car body.
This is sometimes not an actual wired connection, but the metal body (or part) touching the car
body. As current flows across this point, and it is usually a contact between two different metals
(eg. Aluminium and Steel) it’s the perfect place for electrolysis and corrosion. (Trust me on this
one, I had a Range Rover before the Alfa – aluminium body panels, steel body panels and Lucas
electrics. And all this time you thought Italian electrics were dodgy.
If there is an actual earthing wire, make sure that connections at both ends (the item and the car
body) are good. This is where a multimeter comes in handy, so go and buy a cheap one from your
local Dick Smiths, Tandy, etc. You only need one that measures voltage (DC) and resistance (),
so don’t be tempted by an expensive one with a lot of flashing lights and buzzers. The resistance
from the item to the car body should be very close to zero. If you get a reading of more than a
couple of Ohm’s (), pull the connections apart at both ends and clean them thoroughly. A small
piece of steel wool can be used lightly on most areas to remove corrosion.
Then you can go on to making sure that the item itself isn’t earthing out internally. Moisture build
up, corrosion or a loose wire or connectors are the usual causes of this. There are too many
variables to go into here but if you have a particular problem, e-mail me and I’ll explain (or try to)
individually. If an item is not working properly where it is in place, you can remove it and using a
couple of spare bits of cable, connect directly to battery terminals. Make sure you get the polarity
right or all of the smoke may come out of the item (+ to + & - to -)
After making sure that the Item itself is OK, start with the plug to the item and work your way
back to the switch. Check the cable where it goes through grommets in the rear compartment or
the firewall. This will make sure that the insulation isn’t damaged (unlikely, but it can easily
happen if you are a fiddler like me, if someone else has been working on the car or if major parts
have been moved about ie. Seats, carpet etc.) While your checking the cable, check any
connectors you find. Don’t just look at them, pull the connector apart and look at the individual
pins and sockets foe signs of damage or corrosion. Just remember to plug them back together.
Then you come to the switch. This is more likely to fail totally than earth out, but the cables &
connectors on the back may cause a problem. I have seen some switches melt and short out
(Lucas electrics again), so if it happens consider installing a relay and fusing the circuit
individually.
The + supply from the battery will “usually” pass through a fuse, and often a firewall connector,
another switch (eg. Ignition) or a relay before it arrives at the switch for the item. These are
possible points of failure as well, so they need to be checked.
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Electrical Fault Finding on an Alfa Romeo 90
Individual Faults.
1. Tony sent me an email asking about a problem that a few people have had, where instruments,
lights etc. dim and brighten in sync with the indicator flashes. This sounds like a perfect example
of a poor earth somewhere. The most likely place would be in one (or more) of the lamps
themselves, or the flasher unit.
The first place to start would be if you have a trailer plug fitted. It’s exposed to the elements, gets
covered in road grime and is usually overlooked as a point of failure. Try cleaning it out (inside as
well) and making sure the connections are good. If in doubt, follow the cable back to where it
joins into the cars electrical system. I have seen some really dodgy jobs with trailer lamp wiring
(and stereo/speaker installation) where the job was done by a “professional”, but consisted of the
wires stripped of insulation and twisted together (if your lucky you might get the joint wrapped in
insulation tape)
If the trailer plug looks OK, the next place to look would be in one of the indicators. Follow the
procedure on page 1 (don’t forget the little repeater lamps on the side). The Alfa 90 has easily
checked rear lamps, as the whole board un-clips, but I had a bad connection on mine when I first
got it. This was because the track on the circuit board where the connector plugs on was damaged.
I have access to a circuit board repair facility, but if your able to use a soldering iron you can
probably do a good enough job yourself. I haven’t pulled the front indicators off yet, but it
doesn’t look real hard.
Although the symptoms I have been given imply the flasher circuit is the problem, You could also
check the connectors to the instruments (if they are the only thing that flashes in sync). As the
problem seems to be broader than just the instruments, it is unlikely to be something other than
the flasher circuit.
If the lamp earth return plugs on to the little earthing points on the front cross piece, that could be
a fault spot. Clean the pin and socket and try again.
Another biggie, check your earth return lead from the car body to the battery negative (-) terminal
is making good contact – especially where it bolts on to the body (corrosion and electrolysis
again)
One last thing, have you checked your alternator output voltage? The regulator could be shot,
causing a drain on the system when a load is applied, causing a voltage drop.
Is the synchronised flashing only at idle, or does it also occur at revs? If at idle only it could be a
faulty charging circuit not putting enough into your battery. Your battery voltage (engine off)
should be 12 V or a bit above. With the engine running your alternator output should bring your
voltage up to between 13.8V and 14.2V. If you need it checked, most auto electricians will check
it on the spot for free.
If you have tried all the above, drop me a note with specific symptoms and I’ll see if I can help
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