First drive of the season- Lights dimming at 5K rpm

esmeby · Post by **esmeby** » Wed Mar 24, 2004 10:55 pm

Just took the first trip around the block, I noticed that my headlights lights dim at about 5k rpm under load. Doesn't do it by reving. It is like a switch at 5K, no gradual dim, but a quick dim down to about 1/2 brightness. I only noticed that the headlights dimmed, I didn't notice if the dash lights did.

Background:
U-20 with a Gary Boone dist.
Car has been sitting in an insulated garage since fall, battery unhooked. It started very easily with only about 10 sec of cranking. I noticed the lights after about 10 minutes of cruising to get it warmed up. Ammeter shows slightly on the + side on most rpm, aftermarket voltmeter is at about 12.

Any suggestions?

oilleak · Post by **oilleak** » Wed Mar 24, 2004 11:13 pm

Typical problem. the points in the headlight relay bounce at a certain rpm usually right around 5K. I haven't had the problem myself but it's fairly common. You can clean up any corrosion on the relay points, make sure it's not loose so it can't vibrate on the fender, or possibly bend the spring with the points a bit to add pre-load. Someone who's had that happen ought to chime in with exactly what they did.

Post by **S Allen** » Wed Mar 24, 2004 11:48 pm

I have not had it happen but Brian is correct in mentioning the headlight relay points. As with any 30 plus year old part things go wrong after a while. You should be able to carefully pry the cover off and gently file/clean the point up and check for broken parts. Put it back together, hook it up, and your fluttering lights at speed should have gone away.

Steve

TR · Post by TR » Thu Mar 25, 2004 12:11 am

Also make sure your high/lowbeam selector switch is making solid contact and is not corroded...TR

SLOroadster · Post by **SLOroadster** » Fri Mar 26, 2004 8:39 pm

I know what your talking about. Mine nearly go out at 6000 rpm, ususally when I am doing stupid stuff in the dark on a back road at night. In 5th my lights nearly go out but at freeway speeds (about 5000 rpm) I'm OK. I have been trying to deal with that one for a while.

Will

ianmiller07 · Post by **ianmiller07** » Mon Mar 29, 2004 9:39 am

Does anyone know of a solid state relay that could be substituted for the stock one? My relay is tired and will release the highbeams when I go over a bump, its a little unnerving.

SLOroadster · Post by **SLOroadster** » Mon Mar 29, 2004 8:46 pm

I'm not sure but, you might pull the turn signal/ high beam switch off and see if the switch is making contact. I've had that problem and it was in the switch on the colum.

Will

TR · Post by TR » Mon Mar 29, 2004 10:55 pm

Will is 100% correct! The combination of the two (light corrosion on the switch and old relay) can yield very poor lighting.

Make sure the contacts for the switch are clean and corrosion free...Can be done with only the steering wheel off.

As for the relay, there is absolutely the needed part out there. What you need is a relay that has a normally closed circuit and an activated circuit. A quick look in digikey for automotive relays should yield the part you need...A 12V SPDT relay capable of handling a surplus of power (Don't want this one to burn out on you) will do the trick...

Here's how to hook it up (relay terminal TO connection)

30-Power TO Headlight On/Off switch
87a-Normally Closed/Activated Open TO Lowbeams
87-Normally Open/Activated Closed TO Highbeams
85or86-Signal 1 TO Headlight On/Off (Same as Power)
86or85-Signal 2 TO High/Lowbeam Slector Switch

Note the somewhat odd configuration of switching the relay activation with a ground signal due to the way Datsun made the High/Low Selector.

Happy nighttime driving to everyone! TR

DatsunBucky · Post by **DatsunBucky** » Tue Mar 30, 2004 4:19 pm

Would rigging some sort of rubber isolation pad for the relay mounting help?:?: Whatever you've done to fix the original problem could conceivably fail/cause trouble again at a later date since the vibration is still there. Seems to me that keeping the vibration from even reaching the relay would alleviate any problems of that sort in the future.

TR · Post by TR » Tue Mar 30, 2004 10:28 pm

The mass of the switch mechanism in modern relays is much, much lower and the pull force of the activator much, much stronger-that makes them much better devices...

The old ones might be helped with some isolation...TR

esmeby · Post by **esmeby** » Wed Mar 31, 2004 11:18 pm

One more night drive. I cleaned the headlight relay, and also cleaned the voltage regulator contacts a bit.

Now the headlights don't dim at 5K, but sporadically all the lignts (including dash) dim. I wouldn't say it "flutters" but it is a sporadic and quick dimming. When it dims, ammeter shows negative, volt meter shows 10. This happens at all rpms.

If I wind it out a bit, all lights brignten up, meters go positive, but not for long.

So I am guessing it could be the battery, regulator, alt or the "mystery bad ground" somewhere. I have a hand held voltmeter whcih I sorta know how to use. Can anyone give me a few pointers on tracking this one down.
Electronics are not my strongest area (along with carbs, timing, tranny, brakes etc...), but I believe if the battery was the problem, the gauges would show full positive. The battey is about 4 years old.

Springtime car issues are normal for me, but this is the first time that I registered and pre-paid for the novice AutoX class in my area (my car seemed fine at the time). I need to get this sorted out within 2 weeks of working on it after the wife and kid go to bed.

Would the GM 1-wire conversion be my salvation?

TR · Post by TR » Wed Mar 31, 2004 11:55 pm

This sounds a bit like the a charging system going bad (alternator & regulator), but could also be the wiring harness under the dash that causes cars to burn...

The one wire might solve the issues if it is a charging issue, but I'd hate to suggest doing the conversion right before racing season. You could buy a bunch of new batteries and run a "dead loss" system!

I would really check under the dash and see if that harness is about to go. You may want to bypass the harness wires for the amp gauge with new ones as a temporary fix, make sure to fuse the lines, too.

Good Luck Racing! TR

esmeby · Post by **esmeby** » Thu Apr 01, 2004 12:16 am

Couple of things. When I moved the alt to the cool side of the car, I replaced the wire leading to the ammeter and put a 30A fuse on it.
I need to also drive home from the autox, so I would rather fix it than work around it.

My car was a bastard collection of parts when I got it. The harness was awful with lots of temporary fixes done on it. Being on a budget, I replaced the harness with a mostly unmolested one from a 70, while my car is a 68 or 69 (not exactly sure) There were a few minor differences, but all has worked fine for 2 years now.

IE my volt regulator has 6 wires coming from it, but the harness has only 5. The harness has 3 wires that plug into the alt, but the alt has 4 wires in the plug. The wiring diagram is more of a theoretical guide than a map.

The more I think about this, the more I am leaning towards the 1-wire deal (or a used Miata)

TR · Post by TR » Thu Apr 01, 2004 2:05 am

That does make a case for the 1 wire! You said you were not sure how to use a meter, but you sure did a lot of wiring to that car!

That is good news on the fuse to the amp gauge, you sure see a lot of Roadsters with fire damage that started under the dash...

As a general check...If the lights only dim when the engine is running and the volt and amp gauge read similarly to when the engine is off, you can assume it is a charging issue. If the lights dim and the gauges read less than on just the battery, you have a fault somewhere...

Please let everyone know what you find...TR

Datsun Roadster Forum-311s.org

First drive of the season- Lights dimming at 5K rpm

First drive of the season- Lights dimming at 5K rpm

RE:Lights Dimming At Speed

Dim lights

High beam issues