Why No Driver Side Main Beam... Help!?

Anyone able to shed some light... excuse the pun?

I have an '85 90 2.5 N/A...

Everything functions correctly on the passenger side circuit (side light, dipped beam and full beam), however selecting full beam causes the driver side dipped beam to drop off, leaving nothing illuminated other than the side light - how so?

I have 3 wires running to the lamp holder: BLUE/BLACK, BLUE/ORANGE and BLACK all of which appear to be in order and I've even tried bypassing the lamp holder (3-way connector), by connecting each wire directly to the corresponding 'tab' on the lamp, but the same thing occurs! How can everything operate correctly at dipped beam, yet drop-off when full beam is selected... I've tried 3 different lamps, to eliminate the possibility of a duff one!

Not sure I understand?

When you select main beam you turn off the dip so if you have a fault in main beam (either at the bulb or the circuit ) then you will be left with just the sidelight.

You've tried different bulbs, and the passenger side main beam works. Therefore the fault lies somewhere in the driver's side main beam circuit. Obvious first check would be the fuses. Next get a multimeter and check for voltage at the connector. Work your way along the circuit until you find the fault.

Thanks both for the pointers.

Just checked the cabin fuse box and it's shocking - if I wasn't such a dimwit, I'd have done that first-off! A delightful mix of incorrectly rated fuses, blown fuses, a partly melted plastic fuse holder, slivers of tin foil and mud/grit/dirt aplenty! Makes me wonder what the P.O. was all about!

I can see from a quick web search that upgrading to a spade-type fuse box is a popular mod - I'm going for the 'easy option' first and will replace the glass cartridge fuses, after a thorough clean-up of the fuse box. If this doesn't work then it'll be upgrade time.

Thanks again.

First thing is definitely to change the glass fuses for the correct ratings- these should be marked on the fuse box cover.

I converted mine to blade fuses while I was doing some other work and it's a worthwhile conversion. There's nothing particularly 'wrong' with the glass fuses but they are quite bulky.

You can fit three 8-way fuse boxes in a space not much larger than the existing fusebox, which gives room for future expansion. For example, I rerouted the wiring to the radio to bring the fuses into the central fusebox rather than stuffed down the back of the dashboard. It's always handy to have a couple of spare slots so you don't end up with fuses scattered randomly when you add a circuit. Plus you only have to carry one type of fuse rather than two.

Thanks again Pete - I really appreciate your guidance on this. In all probability, I'll go the conversion route when I get a moment.