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MG MGB Technical - Headlight Blink What do you think

1967 MGB. You guys were right when you told me to check the headlight connection near the bonnet latch recently when I replaced the right side lucas headlamp and it did not correct the problem. I unpluggged the bullet connecter and although it looked fine, once I plugged it back it worked fine. Now a few days later, the other halogen light I put in at the same time blinks off for a few seconds then comes back. It does NOT seem to be related to bumps but rather acceleration and RPM..? Is that circuit somehow influenced by the generator? Does halogen affect this. It sure seems strange and related to engine as opposed to loose connection. Wiring is totally correct and unmolested after 8 year old restoration and no water ever. Thanks
Ralph

Ralph - The fact that after the connector had been unplugged and then reconnected, the right side light started working tells me that your connector (regardless of how good it looks) is being affected by corrosion or a loose connection (after 40 years of working electronics, it scares the hell out of me to have an item start working all on it's own after being unplugged and reconnected - it will ALWAYS fail again at the worst possible time). At the very least I would suggest that you unplug all of the bullet connectors in the headlight circuit and clean the bullets very well with a small wire brush and then replace all of the sleeves. You can get new sleeves (and anything else you need for the wiring) from British Wiring at http://www.britishwiring.com/
You should also check the grounds for each headlight, making sure that the ground point is well cleaned down to bright metal and preferably coated with a conductive grease such as Koper Shield from Thomas & Betts. The headlights, particularly halagons draw a lot of current and it doesn't take much resistance in either the line for the power or the ground to drop most of the 12 volts being supplied.

No, the generator would not cause one light to fluctuate without causing bothe of them to do the same thing. Anything associated with the engine, even the engine to body ground wire would cause both lights to react the same way. Your statement about the wiring being unmolested for the past 8 years says volumes. After 8 years, the wiring, with connectors that are essentially open to the elements are probably developing corrosion, so the above cleaning/renewal is definitely in order. After cleaning each connector and after reconnecting it, smear some dielectric grease, such as sylglide around the wire where it enters the sleeve to seal it against the atmosphere. Good luck - Dave
David DuBois

Ralph,

Dave's advise, as usual is top notch.

Another area I would check as I just recently had a similar issue, is the floor dipswitch connections if fitted to your year. My highbeam connection was corroded and only worked 20% of the time--the other 80% would leave me in the dark! Upon examination, much corrosion and a melted wire!

Dave, thanks for the link to British Wiring. I'll be calling them today!

Cheers

Paul
Paul Hanley

Ralph,

Now that I've had my second cup I realize your dipswitch is not likely the issue or both lights would be out. Since I was two steps from a fire though, I suggest you check & clean those connections anyway as part of general maintenance.

Paul
Paul Hanley

And while you are at it treat it to new connector sockets, and when you reassemble them do so with Vaseline. Not only does it make them easier to get fully seated but it helps keep out dampness and corrosion. It is important to get the bullets fully seated in the connectors, they seem to stop when pushed so far but usually need to be pushed a bit more for a second 'click'. I cut a notch in the end of each handle of a pair of pliers the width of wire which has made the perfect tool to squeeze two opposing bullets in at the same time, and it also does singles where there are only three wires in a 4-way connector. The connectors by *either* headlight can affect the left-hand light, of course.
Paul Hunt

If you are not ready to perform surgery on your plier handles as Paul did, British Wiring carries a set of pliwers specifically for the purpose of properly seating the bulletsin the connector, however the price make home surgery look good. Cheers - Dave
David DuBois

Question for David: I was told by someone (Jeff Zorn at LBC I think)who seemed knowledgeable, that halogens are brighter because the gas in the bulb helps wire to glow brighter and they didn't draw more current though the bulbs might be hotter. I was asking at the time because I was concerned about putting additional stress on the wiring. Always try to challenge what I think I "know". Thanks for any info.

JTB
J.T. Bamford

True within reason - look at the wattage on the bulbs. Standard halogens are 60/55, as are late sealed beams. Earlier sealed (and non sealed) were less, like 55/45 (about right for 67), or way back 35/35. Your car should be happy at 60/55, if you get the wiring straight. Jeff's explanation is correct, and it's why the halogens put out more light. If the voltage is right, the gas fill causes the vapors from the filament, which usually deposit on the glass, to be redeposited on the filament, so keeping the glass clear and the filament from disappearing altogether. Either too low or too high voltage is evil.
FRM
http://www.usachoice.net/gofanu
FR Millmore

To expand a bit on FRMs explanation, the standard halagons purchased from Auto Zone and such are 60/55 watts with some going as high as 65/55 watts (usually the rectangular bulbs). A headlight with the high beam rated at 60 watts is going to draw 5 amps and 4.58 amps at the 55 watt rated low beam. This is 9.16 amps for both headlights on low beam and 10 amps on high beam. This doesn't sound like a heck of a lot of current until one realizes that the generator only puts out 22 amps at 4000 rpm. With that in mind, the headlights are drawing up to almost half of the generator's rated capacity at 4000 rpm (how many people drive around all the time at 4000 rpm?). Now, if one has gone out and purchased some of the high end halagon bulbs that put out on the order of ten thousand candle power (to try and compete with the good old boys in their wacking big 4 X 4 pickup trucks), the current requirements can rocket straight up to the point that the generator can no longer supply the current required and the additional current is being supplied by the battery. The result is dim headlights - perhaps brighter than the original headlights, but dim compared to what they are capable of.

Ralph - to go back to your statement that the blinking of the left headlight seeming to be when the engine is being reved up, the short answer (that I gave you earlier) is that the generator won't cause this. When one starts to add up all the current draw when the car is running with the head light on and perhaps the heater blower and maybe even the wipers on, plus the dash lights being on, the poor old generator is really being pushed to it's limit. At this point the head lights may be a bit dimmer than optimum (but not dim enough to be really noticed) and if a connection or ground to the left headlight is something less than perfect, it is conceivable that reving the engine will cause a momentary increase in voltage enough to overcome the marginal connection and cause the light to blink on or off momentarily. This is rather streatching for an explination, but I suppose that it is in the relm of the possible. It still goes back to those 8 year old connections in need of some attention and even upgrading the ones that are carrying the most current (such as the headlights) to the Posi-Lock type of connetor that I spoke of in the original posting. Good luck - Dave
David DuBois

I rewired a car that had uprated halogens, and fitted headlight relays and fuses as part of the work. Afterwards the owner said the difference was amazing. As well as being noticeably brighter the switching between the two beams was instant instead of a period of darkness followed by a ramping up. If you are going to the trouble and expense of fitting 'better' lights it seems foolish not to get the best out of them by bypassing the 30 year-old switches and connectors.
Paul Hunt

Relays provide other benefits in that the amount current going through those 30 yr old switches is no longer the same as required for the lighting itself. It is reduced to the level required to close the relay's switch, usually several orders of magnitude LESS than the OE setup, and that allows those switches (30 yo or replacement) to last a good deal longer than they would have in the original configuration. And it does this while drawing less current through the wiring harness that provided current to those lamps, allowing other items branched off from that harness to have less competition for the power that harness can provide.

Altho the OE harness can work OK without relays, it is demonstrable that it works much more efficiently without those higher halogen loads in combination with the other demands placed on it from the heater fan, wiper motor, rear window defogger, stereo sound system, etc. In my own experience, installing relays for the halogen headlamps all by itself allowed my dash lights to unexpectedly increase in brightness, even tho the dash light circuit had not been touched in the process, other than removing the headlamp current draw from the OE harness.
Bob Muenchausen

Thanks for the info. Didn't mean to hijack the thread. Be interesting to hear what caused Ralph's problem.

JTB
J.T. Bamford

This thread was discussed between 19/10/2004 and 20/10/2004

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