Main Beam Headlight Strange Fault

JVY

JVY

Active Member
Hi,

after refitting my headlamps, I decided to give them a check and came across a slighlty curious problem:-

with the lightswitch on the dash truned to the headlights position, at the front of the car I got sidelights and outer headlamp dipped beam (all as expected). When I switched the main beam lever on the steering column up to the ON position, only the outer headlamp main beams came on (i.e. no inner headlamp main beam). So, I thought I have probably blown a fuse while I was welding. Sure enough, checking the fuses, I found the one that feeds the inner main beam headlamps was open circuit. I replaced the fuse an did my test again.

This time, with headlight switch on the dash to headlights, I got the same results befoore (dipped beam on the outer headlamps as expected). However, flicking the the main beam lever up to ON position, I got no beam beam on any of the x4 headlamps! When I pull the main beam lever into "flash" position, all x4 main beams do flash on as expected.

Had a quick look at the wiring in dash/headlamps and all appears to be standard as per the Rover wiring diagram. After a bit of head-scratching and trying a few different things, I found that I could get everyting to work as expected by partially removing the inner main beam fuse! Basically, I just pulled the 32mm fuse out of it's lower clip and left it so it was just touching the bottom fuseholder clip but not actually clipped in. With the fuse like this, I can switch the main beam on as expected on all x4 headlamps by putting the steering colum lever up in to the ON position.

The only theory I can come up with is that the contacts in the steering lever switch have "carboned up". From the above, the switch will happily switch only the x2 50W outer main beams on. However, with the inner main beam fuse fitted, another x2 75W lamps are added to the circuit. This gives a total main beam power of 250W at a current of about 21A. I am wondering if the high current surge or arcing through the main beam switch is heating up the carbon on the contacts and ausing it to open circuit. Can I strip the main beam switch on the steering column to look at or clean up the contacts?
Has anyone seen anyhting like this before or do you maybe have any other ideas?

If I can't clean up the contacts I am thinking that I will have to try to obtain a new known good switch or maybe look at fitting a relay to switch the main beams?? 21 Amps does seem like a lot of current for a small switch that is quite frequently used.
 
I think the switch on the steering column feeds both inner and outer so if it was carboned up it would affect both sets of lights.

The fuse that you pulled out, have you checked that both contacts at the top of the fuse are making contact with the fuse? IIRC the circuit is wired such that the main beam flash circuit goes through the RHS contact and the permament "ON" main beam circuit goes through the LHS contact. That tends to be why moving the fuse causes the circuit to make and break intermittently.

Pulling the fuse out at the bottom might have moved the top of the fuse sufficiently to make contact with both sides.

Worth a look.

Dave
 
I agree with Dave

The S2 fuse box is a well known hazard area in the P6. It is made from a plastic that melts very easily and will also spontaneously combust with not a lot more. Consequently, the clips that hold the fuses very often have moved apart slightly under the influence of soft plastic in the base. This always shows up first in the main beam headlight fuse. Things can be helped along by someone having used metric fuses which are just very slightly shorter than the pukka imperial ones. That's enough to raise the temperatures high enough to get the melt going. So, start by making sure you have imperial fuses. Next go round the fuse box and give the fingers a squeeze together to make sure they are gripping the fuses properly. Finally, if you are feeling athletic, go round all the incoming and outgoing wires and crimp up their conections into the fuse box. I'd recommend having the front seat and runners out and the glove box off for that one!

I think that what you have done in partialy withdrawing the fuse is to tilt it slightly, thus guaranteeing you get a good contact across the fuse between the two blades at that end.

It is possible that the headlamp dip switch is crusty. as well. When I first started using Lucky after he had had a long lay off that switch needed quite a lot of encouragement. I simply moved the swich rapidly to and fro whilst holding the lever down firmly. Did the trick and never looked back - I did have a spare switch handy though!

Chris
 
Dave & Chris,
thank you. The advice to checkout the fuse clip contacts sounds very good. It makes sense & I shall check this out before I do anything else. I now recall that I have read once or twice that the P6 fuse boxes heat up and go soft causing the contacts to move apart. The top contacts do seem reasonably tight. However, I didn't realise that the feed to the holder was just through one side of the contact. Some further investigation with multimeter is definitely in order.

Good advice too on the metric/imperial fuses. The fuses fitted are mostly marked Lucas and look like the proper 1.25" type.

Will let you know how it goes & thanks again.
 
Chris/Dave,

you were spot on. I had a quick look last night. Although the fuse holder clips at the top of the main beam fuse seemed to be reasonably tight and making contact with the top of the fuse, I carefully nipped them in a little with long-nose pliers. After that, everything worked as it should :D :D :D :D .

I am guessing that the feed to one side of the top clip on the fuse holder comes from the main beam flash switch on the steering column and the feed to the other side of the clip comes from the main beam permanently on switch. This would explain why the main beam flash worked and but the main beam permanently on didn't.

I wonder if a simple modification that would help prevent this fault and tend to reduce the heat build up in the fusebox would be to connect the two sides of the fuse clip together? How easy is it to remove the fusebox to do this? I suppose even jumpering the two woires from the main beam switches together as the go into the fusebox might be an easier mod that would have the same effect (though it is a bit more "Heath"). I was even tempted to leave the cover off the fusebox to help keep it cooler but decided this was unsafe.

Once again, many thanks for quick & excellent advice. :D
 
JVY said:
I am guessing that the feed to one side of the top clip on the fuse holder comes from the main beam flash switch on the steering column and the feed to the other side of the clip comes from the main beam permanently on switch. This would explain why the main beam flash worked and but the main beam permanently on didn't.
Click to expand...

Absolutely correct. Glad you got it sorted.

I wonder if a simple modification that would help prevent this fault and tend to reduce the heat build up in the fusebox would be to connect the two sides of the fuse clip together? How easy is it to remove the fusebox to do this? I suppose even jumpering the two woires from the main beam switches together as the go into the fusebox might be an easier mod that would have the same effect (though it is a bit more "Heath"). I was even tempted to leave the cover off the fusebox to help keep it cooler but decided this was unsafe.
Click to expand...

The point to be aware of now is that with prolonged use of the main beam it will happen again. There must be a reason why Rover wired it up like that. Without the wiring diagram in front of me I wouldn't want to comment with any certainty on the effect of connecting the top 2 blades of that fuseholder together. Best thing to do is fit a relay into the main beam circuit to reduce the current, and therefore the heat, through that fuse. Problem solved.

Dave
 
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