Fuses have started blowing. The fuses blowing seem to be related to the clock, instrument panel and brake lights (6 and 9 I think). The fuses only seem to blow when the car is in motion.

Reading the voltage from engine block to battery positive terminal, at idle I get 13.5v, turn on all the lights, fans on full and I get 11.9 (bear in mind my multimeter is a cheap battery operated one, but there is a consistent measured drop of 1.6v).

Low voltage, and voltage drop under load, would seem to point to either the alternator or voltage regulator? But would this cause fuses to blow?

(Have had a quick look for a short circuit but not found one yet).

Thanks in advance.

I don't know if this is applicable (or helpful ) in these days of printed circuit boards, but back in the old Cortina Corsair days there use to be a seperate little silver voltage drop box for the instruments on the old Fords which occasionally - though very rarely used to pack up. Don't suppose there's on in your Haynes wiring diagram??

There's nothing like that, that I can see. Going to try change the alternator voltage regulator.

make sure the chassis to engine earth strap is nice and tight...

Have changed the voltage regulator for one I had laying around. The brushes are noticeably worn but appear to be within limits. Retested voltages. Get about 13.8v idle electrics off and 12.7v all lights and the fans on full. A reduction in voltage drop.

Not yet tested for blowing fuses, will check earthing straps and try a visual check of wires first.

Apparently a failing voltage regulator can cause fuses to blow because as the voltage drops and power needed remains the same, current will go up and current is what causes fuses to blow (apparently - can't claim to fully understand the electrical concepts).

Replaced voltage regulator and cleaned engine to chassis connection and no more blown fuses yet :-)

fuse blown again. Next change the alternator.

I can't see that the alternator will have much to do with blowing fuses. In a circuit V = IR (voltage = current X resistance), as the resistance is fairly constant when the voltage drops the current will drop. Fuses are there to protect the wiring and consumer from damage, if too much current is drawn they will blow.

You need to check each circuit for a short circuit, could it be anything that was disturbed when you removed the immobiliser? Do any of the brake light wires pass through the tailgate?, as the wires that often break where they pass through the rubber grommet in the tailgate.

Only thing I've had done that precedes this is changiing the steering rack and having the tracking done, but as it's non power steering I can't imagine that caused this.

A centre brake light was added by the previous owner so will give this a good look over and rip out the instrument panel etc.

Any ideas how much it's likely to cost to get an auto-electrician to check it out if I fail to find the cause? Everything seems to be happening to the car at the moment so not much cash.

Only thing I've had done that precedes this is changiing the steering rack and having the tracking done, but as it's non power steering I can't imagine that caused this.

A centre brake light was added by the previous owner so will give this a good look over and rip out the instrument panel etc.

Any ideas how much it's likely to cost to get an auto-electrician to check it out if I fail to find the cause? Everything seems to be happening to the car at the moment so not much cash.

From your first post it looks as though you have a pretty flat battery. A fully charged battery might help and is cheap. Have you checked the volts as you increase rpm, they could be going up above 14 if voltage regulator is duff. I've had high volts before and that will blow bulbs. You can keep the volts low by increasing the load as you said. Might get some strange looks if you drive around with lights on in the day.