Voltage questions

[Cutter]

Apologies in advance if this is a stupid question.

My headlamps seem to draw an awful lot of current, which I want to sort out. Regularly I get a reading of 13-14v on my voltmeter, however when I turn on my running lights it drops to 12 and headlamps it drops to 11, closer to 10 with the heater on. I had the stock alternator checked out by a shop a year ago and it is fine, and the battery is a new optima. It never seems to get down to 10, and if I turn everything off the reading turns back to 13-14 after half a minute or so.

The PO rewired the headlamps trying to a short that I discovered was in the signal stalk/highbeam switch, and I'm thinking there may be a draw there. Or is this to be expected with the anemic lucas alternator? A friend said something about the voltage regulator may be going, but I will admit to being a novice when it comes to automotive electrics.

[I Leak Oil]

1) Check the ground.
2) Install a relay.
3) Ditch the lucas and install a delco.

[Terrys]

Cutter, are you taking these readings at idle or at a raised rpm, say 2k?
There are alternators, and then there are alternators. Do you know offhand how many amps yours is good for? You may want to consider a larger unit, perhaps something on the order of 75 amp.

It is certainly possible that you have some other low resistance draw, but it would seem likely, if you did, that smoke would eventually appear.
If you have a good ammeter (not a dash type, but a digital, or analog test meter, you can verify that your lights are the only draw. Even the better VOMs only have a 10 amp range, usually a separate socket than the normal V-O-M readings socket. You would need an ammeter capable of perhaps 20 amps. Start by putting the test instrument in the black ground line from each headlight plug, then add to that the reading from the other. This will give you the total current draw of the two headlamps, and nothing else. Finding a wire that you can interrupt with the meter to reading the cumulative side lamps and dash lights might be a little more tricky, but if you have the vehicle schematic, you can do it. Next, you would need to put the meter in the line (brown wire) from the solenoid to the fuses. If you get a higher reading than what you added up from the individual circuits, then you do have some other high current, low resistance load. Often, this can be the actual headlamp switch contacts. If this were the case, a relay headlamp conversion would help.
Given the fact that you have been having the issue for a while, without smoke, I'm inclined to think your alternator just isn't delivering the current necessary.

[73series88]

yeh i have a lucas alternator on my truck and i notice when i have my lights, wipers, heater and other accesories on everything dims down.
im going to put in a ac delco when this one goes. especially whith my new summit heater on the way.
aaron

[mongoswede]

I seem to remember that the earlier alternators only put out around 35 or 40 amps..the later ones are 60 amp? Power/Voltage = current. A pair of 50 watt headlights (100 watts for the pair) will draw 8 amps at 12.6 volts. By contrast most modern cars are running between 80 and 120 amp alternators.

Without swapping in a nother alternator you can make life a little better by installing some good heavy batter cables and running a few more ground straps. I have made battery cables with 2 gauge welding cable in the past and it works amazing well. Your local welding supply store should be able to sell you a 20' length for $30 or $40 at todays rates. You need a big crimp tool and some copper 2 gage eyelets. I also replaced my battery terminals with Marine style making it easier to attach the beefier cables. In addition make sure all of your battery terminals are clean and all of your grounds are clean as well.

[Cutter]

Cutter, are you taking these readings at idle or at a raised rpm, say 2k?


This is when running at 2k or above. I had posted on here about a year ago about swapping my alternator out with a high amp unit, but since my engine is a 2.6 I have to make a custom bracket. Not the end of the world, and if it turns out there is no wiring fault, I'll do just that. Thank you for the detailed testing approach, I'll do this as soon as I have time.


Without swapping in a nother alternator you can make life a little better by installing some good heavy batter cables and running a few more ground straps. I have made battery cables with 2 gauge welding cable in the past and it works amazing well. Your local welding supply store should be able to sell you a 20' length for $30 or $40 at todays rates. You need a big crimp tool and some copper 2 gage eyelets. I also replaced my battery terminals with Marine style making it easier to attach the beefier cables. In addition make sure all of your battery terminals are clean and all of your grounds are clean as well.

Yeah, when I replaced the battery I put all new cables and grounds on the battery, cleaned all the contacts and applied plenty of conductive grease to everything. I will probably upgrade the cables again if I throw a new alternator on, I used pretty oversized stuff this time.

[Cutter]

ok my grounds were a mess and that is now sorted, my multimeter is only a 10amp unit unfortunately

[antichrist]

cleaned all the contacts and applied plenty of conductive grease to everything.That could be your problem, you want nonconductive grease, like dielectric grease. If it's conductive you can get voltage leaks around your connections.

[Cutter]

yes, dielectric grease, I always assumed that was to aid in conductivity...

As an update on this, I pulled my battery out to replace my starter solenoid (unrelated) and noticed that the belt tension on my alternator was loose with the improved visibility. It was fully extended on the bracket so it could take any more slack, even after some shims etc. So I'm guessing the alternator slips under the load of the lights. Tomorrow I'll see if I can find a slightly shorter belt at the auto store.

I've got a spare Hella relay harness for aux lights that I might temporarily wire onto my main beams and see if that helps. Anybody know a good online source for waterproof fuses and wiring parts, the stuff at Autozone here is junk.