100 series dash lights

100series will be DOT 3 fluid only - like you say can't use DOT4.

Forgot to add that the brake fluid level needs to be right up to the top - light can come on when fluid is halfway between Max and Min.

Agree : we had this with mates 100 series, a short in trailer plug was the problem .

Yes Gaz the alarm did come on, I would assume if the booster was dead it should effect the feel of the brakes. Did your pedal feel any different while you had the problem.
Cheers Ross.

Rosss,
No mate, the there was no difference in the pedal feel or the brakes, just that awful feeling that there may not any brakes the next time they were needed. The pump was running non stop singing weird songs, but it could have stopped at any minute and then, well............Oops, sorry. :)

Hopefully your mechanic has a diagnostic machine and it should tell him what the problem is.

Had the same intermittent fault a couple of months ago. Ended up being an open circuit in the ABS pump motor, this was also pulling the battery down over a couple of days. Changed the whole master / pump/ booster unit and all is good. Easy to change yourself if you have a 10mm pipe spanner. To bleed you just turn on the ignition and the pump will pressurize the system, undo the furthest away rear bleed nipple and it will pump out the air quick as (keep an eye on the level in the master). The brakes were still working perfectly the whole time. I intend to pull the motor off and rebuild it and keep it as a spare.