412 Electrical Problem
 

My 412 electrics are being temperamental. It has a new alternator, regulator and battery and charges nicely at 13.5v. and then it just drops at random to 11 volts or so. Turning systems like the stereo, lights or heater on or off makes no difference and doesn't trigger or solve the problem. The fault seems to be intermittent but has already claimed two alternators, a regulator and a battery it seems to be pretty destructive. How would you tackle it?

regards

Paul

I would check all the main electrical connection forst in case there is a high resistance somewhere. So main battery cables (especially the earth) and the main cable to the starter motor.

Is there a separate heavy engine-to-chassis earth cable? Check that.

But a major problem with the regulator and the cause of intermittent faults is that the regulator BODY must be earthed, and earthed properly.

Down to Earth
 

Hi Paul,

Almost every time I've had an electrical problem on a Bristol it's either been due to an Earthing issue or a cable of the wrong value.

Of course you could have a virus.

Did you ask Sid? He diagnosed and cured my last electrical problem without even seeing the car!

Regards

Richard

Thank you for this, I will check that that is the case and report back

Hi Richard, I wonder if it is a loose earthing cable. As 412s use an Apple II operating system they just can't get viruses :)

I believe Sid sorted your window problem by suggesting an upgraded cable, have you shared that solution elsewhere?

P

Almost every time I've had an electrical problem on any car it's been an earthing problem.

With the exception of my Landrover Discovery, but that's really a collection of small dedicated computers cobbled together to look like a car. Either that or it's an AI experiment.

Short to earth?
 

Hello Paul

If it's taken out the battery and alternator and drops the voltage could it be an intermittent short to the chassis? On the subject of bad earth connections I believe that there is a portable signal generator you can buy that injects a signal and helps to trace earth faults.

Regards

Richard

Hello Paul

Another thought is that the main cause of an alternator dying is a flat battery as this puts extra strain on it. Perhaps you have a short somewhere flattening you battery? The way to tackle the fault is logically, which is what you're doing.
I think if you were to take it to the extreme you would disconnect everything electrical, but the basics and then add each circuit in turn until something shows up.

Regards

Richard

After much investigation and head scratching the problem has been resolved. The alternator, regulator and battery were fine as were their earths. The problem was tracked down to the ignition feed system and BCL advised (I couldn't drive it far enough to get it to them) that the problem is that the ignition system is overloaded and the problem is resolved by rewiring the ignition feed system so that it runs via relays. They briefed the electrician and after a couple of hours work it was all done. Having been told the solution, I then immediately remembered that a Brigand owner had told me last year about having the same problem which was solved in the same way. If only I could have recalled that a month ago!

P

Hello

Yes, we also had our ignition rewired after a burning smell.
A lot of current passes through the ignition switch, a relay system is a very good idea.

Richard