Pulsing electrics?

Not SUPPOSED to be connected....

It sounds to me like you have managed to wire the heater through the instrument voltage stabilizer. On an older car this is a mechanical item, it's just a bimetallic strip with a coil of wire around it - if the current through the coil rises too far, the bimetal bends and breaks the circuit, then cools and makes it again. You don't normally notice this pulsing effect because the gauges are very low current and also slow to react.

surely if its running from the same fuse then its now the same circuit? and scary's relpy very much still stands???

I've just read all this again, has he managed to use the the voltage stabiliser for the gauges, as a flasher unit on his blower motor? To be fair thats quite a feat if so.

the whole car only has 2 fuses and the wiring at the fuse box hasn't been touched. Only 3 wires have been disturbed. The earth wire to the warning light cluster and the two wires to the regulator. I haven't been near the fuse box other than to pop in a new fuse or the blower switch which is miles away from the stabiliser.

I'll get a scan of the wiring diagram up when I get back home tonight

Make sure you drop it on something soft - you wouldn't want to oval the case ;D


Seriously though, either the live side is feeding throught the VR or as rev says the earth side of the blower is only connected to the clocks and not a true earth. Rule out the VR by putting the blower motor on and unplugging the voltage regulator. Also, make sure the fuse is actually providing power - a common lucas fault is where the fuse is dead, but someone has run an extra live to make something work and that then feeds all the other circuits through the common connection at the fusebox....

Maybe get an autoleccy to have a look at it before it all goes up in a cloud of smoke?

I wont be using the booster fan until I find the problem. To be honest the wiring behind the dash is an absolute mess! Full of scotchlocks and I must have pulled out 100 dead end floating wires. I might strip the whole lot out and rewire it following the wiring diagram.

In fact have a pic of the dash when I got it now which wire do I cut to disarm that bomb sir?


I don't think even lucas wiring came out of the factory looking like that! Fan switch is the top leftmost switch on the dash and voltage stabiliser bolts to the back of the speedometer.

True enough Ohms law and all. Of course resistance wont stay constant as it changes with temperature and we all know electric wires heat up. But I can't see that being the problem unless the wiring is too thin and breaking down with heat.

Going by the ammeter alone the alternator does kick out more current that the dynamo did and the wiring was upgraded to compensate. When you start the car you see it charge slightly for a bit before dropping back to showing a very slight charge after a couple of seconds. The dynamo used to be discharging on tickover and only showing a charge when on the move

Resistance changes in adequately-sized copper wire (ie wire that's not starting to glow) are at least two orders of magnitude below the difference between the off-charge and on-charge battery voltages. In other words, it makes no difference.

Yes, an alternator will charge at idle when a dynamo often won't. And the 'spike' in charge current after start-up is the alternator replacing the electricity used to turn the engine over. So it sounds as though the alternator is doing what you'e expect it to do.

However, you are clearly getting interaction between the voltage stabiliser and the heater fan. It is entirely possible that a poor connection in the fusebox is to blame (the fuse retaining clips are normally rivetted to the terminals, and these can work loose over the years). Is there anything else running from that fuse? If so, does it also experience problems? If not, then somehow you've got the heater fan connected into the instrument circuit - although having seen the wiring I can't say I'm enormously surprised...