blown sealed units

Thats my thinking!

Lee D

I would imagine that the rectifier has gone on the back of your alternator.

Meant to say put your voltmeter to AC and meassure across the battery to see if you have AC coming from the alternator instead of DC.

You're not running both filaments at the same time are you?

Certainly relays could remove the voltage drop that might otherwise save you from a high alternator voltage.

Your first comment made a lot more sense!

In message , mark writes

As a general rule blowing of bulbs is a sign of over voltage usually caused by a failed diode in the rectifier not the alternator itself.

i didnt think i would have to say, check for AC ripple voltage when the engine is running. i hope this makes sense now.......... :o)

In message , Dougal writes

2 relays. Each activated by the main and dip wires from the stalk. I've tested the switch with the meter Relays and headlights individually earthed direct to battery. I appear to have current all the way to the units. I swapped the dip beam relay as it was shorting out internally and allowing about 6 volt to the dip even when it wasn't energised; alternator again? After swapping the dip relay everything seemed fine but the units blew again quite quickly.

The alternator is pretty old and been submerged a few times.....

In message , Tony L writes

I'll have a go in the morning...

"hugh" wrote..........

mark writes........

Most likely that it's the alternator regulator that's at fault but have you checked the charging voltage at the battery *and* at the alternator to determine this?. Could be dirty connections on both sides of the battery including engine earths if there is any appreciable difference. The alternator *is* connected direct to the starter solenoid or battery and not to some added ammeter and where are you picking up the power for the relays to the lamps?

A failed diode would more likely drop one circuit and reduce the overall output.

In message , Oily writes

I'll have another look tomorrow.

Direct from the battery; fused natch...

I'll check the voltage at higher revs tomorrow as well..

Solved! I think... Charging voltage was a red herring; my multi is an old analogue job and I need to keep an eye on the 'zero' control :-/

Selecting High would result in a tiny voltage creeping out on the low connector. I had the old girl running for over an hour and eventually noticed that this voltage had grown to 6v. None of this 6v appeared on the 'signal' side of the relay system only on the headlight side. I checked all the runs for earth shorts and then started unplugging bits of loom until I traced it to the remaining drivers side sealed beam. It seems that this was the source of this bogus voltage. The hotter the unit got the bigger the voltage grew. Swap it for another unit and it goes away. So thanks for the suggestion but I'm going to upgrade to halogens :) I may well completely rewire the relay side of things while I'm at it. What's the relay manufacturer of choice these days?

Hmm. The old out of calibration syndrome. A fine example of the uselessness of an uncalibrated instrument. Consign it to the bin of eternal darkness forthwith before it leads you AND US up anymore dead ends!

In message , JacobH writes

Ah but it has two knobs for calibration purposes ;) Unfortunately the knob who should have twiddled the other knob failed to check before using :D

K, but remains uncalibrated is junk, treat it as such.

In message , JacobH writes

Nah. It's fine. I'd been using it during the day and ended up in the dark and the sleet under the bonnet. I do the battery check and check for 'zero' when I switch on but I must have nudged the bloody thing while out in the weather. Re doing the same tests the following day in the light and the dry I sussed what must have happened.

Good old 1980's Micronta ;)