forum.audiv8.com Foren English Audi V8 Forum Electrical problems with warm weather

hi all,

i have a strange problem with my 93 V8, hoping some of you guys can help me..
when its warm weather (+21 degrees Celsius) the speedometer, radio, cruise control and the on board computer all stop working.
everything else seems to work just fine (rpm needle, fuel/oil meters, automatic transmission shifts like normal)
when i put the AC on for some time, everything comes back to live again (depends how warm it is, form 10 to 30min driving)

Does anyone knows whats going on here?

Not really strange...

If the speedometer is down, radio, cruise control an BC got no speedsignal...

The same if the speedometer have a intern loose connection.

It's all about the speedometer, some part in there are sensible to warmth, maybe some (or just one) electrolytic capacitor, but which?

When the slaughter of my silvern V8 is over, I go ahead to check this problem on my own V8, maybe I find something.

ok... but why does the radio needs the speedometer ?

speed signal is needed for automatic radio volume control. It increases the radio volume successively at higher speed.

that makes no sense...

i have a'n after-market radio.. the radio only needs a constant 12v and a switched 12v to work...

how should we know, that your car isn't equipped with a factory fitted radio? Your question was about the coherences between the speed signal and the radio.

In Antwort auf:

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i have a'n after-market radio.. the radio only needs a constant 12v and a switched 12v to work...

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Don't forget ground


In this case it makes really no sense...

Some funny lads don't know how to replace the original connectors for after-market-radios, sometimes the blue/white wire is the problem - the speedometer-signal-wire.... somewere behind the radio... look if it fit well in a (unused) connector.

sorry, i had to mention that i had an after-market radio, installed it myself

if the tacho signal is mixed up at the radio.. then this means the radio doesn't work if i turn my ignition on (not starting the engine) right?
whell... the radio works like normal on colder day's this way...

i think i put my multimeter on de wires, see what i got..
if the voltage is to low, i will go and look i if can bump it up... see what happens

In Antwort auf:

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then this means the radio doesn't work if i turn my ignition on (not starting the engine) right?

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Not right!

For after-market-radio it's not relevant, original-radio don't need the signal, but if it's there, it regulates the volume - drive faster it will increase, drive slower it will decrease...

For your radio you need ground, permanent + and ignition +, permanent + you will find on the original connector, ground the same way, ignition + you will find beneath the passanger floor on the back of one (I don't know which) of the big connectors (black/yellow/red)

i hooked my multimeter on the speedometer wire behind the radio, it gives when the weather is cold like 9 volts, when its hot somewhere around 3 volts...
if i put external voltage (cigarette lighter) on it, the speedo comes back to life...

now the next thing is to look where the voltage drops

Very interesting!

The last two weeks it's seems to get worse... not really high temperatur - no signal... AC lo, eternity for emprovement...

With your description it seems not the signal itself is the problem, more the supply voltage.

Don't discount dry joints, solder connections.

Basically, dry joints are where the solder has not created a good contact between component and circuit board. Age only exacerbates the situation.
Vehicle electronics are full of mediocre quality components that can seriously suffer with age. I've had anomalies on both my ur and v8. In the V8, a few things have randomly been fussy while warming up.

A good quality soldering iron (butane) can be had fairly cheaply, along with solder and flux.