Bristol 603 Electrical circuits

[Peter Hoskin]

Diagram B 680038 'Heated Rear Window, Gauges, Fuel Reserve etc.'
I am experiencing overload on these circuits. Supply comes from Fuse C not Fuse A in my car. The instrument leg shows a 'Voltage Stabiliser" which I have not located. Can anyone describe what it looks like and where it is located? Also can it be tested? Peter Hoskin pjhoskin@optusnet.com.au

[David C]

I don't know the 603 but I imagine it will be similar to this:
https://www.holden.co.uk/p/voltage_s...gative_earth?s

They are used particularly for the fuel gauge to prevent voltage fluctuation affecting reported fuel level. I believe they output around 10 Volts for an input in the range of 11 to 14 Volts.

[Roger Morrall]

It will almost certainly be behind the instrument binnacle since it feeds both water temperature and fuel gauges. Widely used on British cars that used bimetallic gauges, which are characterised by a slow response time from the time that the ignition is turned on. Think Morris Minor. Used to be cheaper than chips. Difficult to test other than by substitution.

Earlier Bristols (to my knowledge up to the 410) used a balanced magnetic petrol gauge which didn’t require a constant voltage. The latter gave an instant response but jiggled about a bit if one hurled the car about and was considered upmarket in its day.

[peter dowdle]

Peter I presume by overload you mean it is blowing fuses. On my 411 and 412 it is behind the the instrument cluster and as advised it simply stabilisers the volts at 10 volts and is only attached to some gauges. I would be very surprised if it was blowing fuses. An easy way to test it is if you rev your motor and the gauges change their readings then it will be faulty. I would be disconecting the other things that are on the same fuse one at a time to see if that stops the problem.

Peter Dowdle

[Peter Hoskin]

Many thanks for all responses, i have learnt a great deal. Further tests of my instrument circuits showed the following:
1) Supply from the ignition switch to the A,B,C,D fuse panel had a faulty connection to the fuse panel,
2) the spring clips retaining the fuses were in some cases rather loose,
3) supplies from C fuse (not A as shown on the wiring diagram). The two green wires supplying the instruments and handbrake warning light were badly burnt.

Replacement/correction appears to have restored everything to normal, the fuel and engine temperature gauges are performing as normal so the voltage stabilizer would appear to be ok.
Where is the stabilizer fitted? Still not known but I recently replaced the instrument lighting with LEDs and saw at the back of the panel steel support frame two metal boxes mounted on the ENGINE Side of the frame at top left and right corner and thinking at the time what a stupid inaccessible place to put whatever they are. One is probably a stabilizer.

I cant be certain what caused the overheating so I have reduced the C fuse to 35 rather than the 50 original and have done about 150 kms without a problem.

[David C]

Something to bear in mind is that the UK at least since 1970 the Lucas rating for glass fuses is the Blow current. The continuous rating is half that printed on the fuse.
Some other parts of the world are the other way around.
A quick check on line suggests that blade fuses are continuous rated.