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Old 11-06-2010, 09:45 PM
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Headlights cause voltage drop

My buddy has a 50 Ford which he rewired himself. He's running a GM 1 wire alternator which is 65 amps. At an idle and higher RPM his voltmeter reads 14 volts of charge. When he turns on the headlights, his voltage drops to 12 volts at idle and only goes up to 13 volts. If he uses the blinkers, it's worse. I noticed he ran 12 ga wire from the headlight switch, etc to the headlights. Will it hurt anything to leave it the way it is? The lights seem bright (halogens), or should we install relays?

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Old 11-06-2010, 10:30 PM
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help for you!

Here is an EZ to read link that will explain things about relays:www.watsons-streetworks.com/current_topic.html when you are done reading that click on relays in the column to the left,I strongly advise getting the 80 amp relay kit to run off the ignition switch to take off accessory load.I am also running the one wire like you,before the relays the original IGN switch failed and I had the voltage drop in my '54 Ford,the problems are solved.The quality of their relays are very good,many aftermarket relays are Chinese junk,Beware! of those.
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Old 11-07-2010, 04:57 AM
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The one wire alternator is your problem you need to change that. I am not saying just change the alternator I am saying change the alternator and wire in a 3 wire circuit. The load balance of the electrical system is incorrect; the one wire circuit is to only charge a battery; when other auxiliarie or external electrical demands are made on the 1 wire circuit; it simply can not keep up with the demand and a low voltage situation is the result.
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Old 11-07-2010, 06:02 AM
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one wire alt

The case backhoe and both forklifts use one wire alternators. I have had a problem running the roof flashers and all the lights , heater etc when running at night.Normally the Case only needs enough to run a diesel fuel solenoid. the injectors are all mechaical. one wire looks neater but if you have a lot of power requirements probably won't do the job.
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Old 11-07-2010, 07:19 AM
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The one wire alternator may be part of the problem, but it also sounds like the alternator is getting weak. At normal operating speeds (about 2000 rpm and up) the alternator should be able to keep it at about 13.8 volts with all the accessories turned on. If you are only getting 13 volts while driving with the lights on, it will still work but you are not fully charging the battery.

I had a 65 amp 10si that gradually got to the point where it would only put out about 11 volts at idle with the lights on, and barely reached 12 volts while cruising with lights and heater blower on. I replaced it with a 94 amp 12si (3 wire hookup) and it completely cured the problem.

I usually get 13.8 volts at idle, and it only drops to about 13.5 when I turn on the lights. As soon as I start driving (rpm goes up) it goes back up to 13.8 volts until the battery is fully charged. The 94 amp 12si is a very standard item, and you can get them from any auto parts store. Just make sure you get one with the right pulley (some are serpentine, and some are v pulley). Also check the clocking of the housing, since that will affect whether the 3 wire plug clears your valve covers and other parts after it is mounted.

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Old 11-07-2010, 08:34 AM
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I have to check but I believe the alternator is a 3 wire alternator. I know it's the 10SI with 67 Amp rating, and it's new. (other alternator snapped a brush). His alternator has the plug on the side of the housing. He has the one 8GA wire from the Red post going to the starter relay. He has a plug which is plugged in the side of the alt. and has two wires. The one wire is connected to the same red post (jumper) and the other is not connected. (not running a alt light on the dash). The headlights were wired with one wire going to each headlight for low beam and one wire going to high beam (total 4 wires). Each headlight is also grounded to the light bucket. When installing relays, does this ground wire at each headlight need to be grounded? Since the relay itself is grounded as well? The diagrams doesn't show it. Thanks for the help. BTW- that was a helpful article on relays, Thanks.
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Old 11-07-2010, 09:04 AM
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Quote:
Originally Posted by kleen56
I have to check but I believe the alternator is a 3 wire alternator. I know it's the 10SI with 67 Amp rating, and it's new. (other alternator snapped a brush). His alternator has the plug on the side of the housing. He has the one 8GA wire from the Red post going to the starter relay. He has a plug which is plugged in the side of the alt. and has two wires. The one wire is connected to the same red post (jumper) and the other is not connected. (not running a alt light on the dash). The headlights were wired with one wire going to each headlight for low beam and one wire going to high beam (total 4 wires). Each headlight is also grounded to the light bucket. When installing relays, does this ground wire at each headlight need to be grounded? Since the relay itself is grounded as well? The diagrams doesn't show it. Thanks for the help. BTW- that was a helpful article on relays, Thanks.
The alternator wiring is your problem. If it is a 3 wire all three wires are required for proper operation.
Large stud to battery power, usually connected to the starter or horn realy.
Terminal 1 connected to switched power usually through an idiot light or straight from a switched source with a resistor
Terminal 2 connected to a power source near the fuse panel. The tells the system how much charge is needed. The alternator will work without the wire but it will be worse than a one wire.

Fix the wiring and most likely your issues will go away.
Relays will make up fro old undersized wiring that keeps the lights from being bright. The do not help with low alternator output. Relays or not it requires the same amount of amperage to run the lights.
If you want to run a quick test, take the wire that is not connected and connect it to a 12 volt source somewhere, you can even temporarily connect it to the alternator stud and see if the voltage comes up.

You need to be sure that the alternator is a 3 wire and not a 1 wire. The look exactly the same and the only real difference is the internal voltage regulator. You may be able to prove it by disconnecting the small 2 wire plug and see if it still charges at all. If it does it is a 1 wire if not it is a 3 wire.

Mad electrical has some of the bect information on how to wire these alternators and why 3 wires just dont work well.
If the one wires worked they would have been in production in GM cars for ever. Think of what they would have saved on wiring. One wires were designen for tractors that had no electrical accessories just to keep the battery cahrged
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Old 11-07-2010, 09:23 AM
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I agree with loose the 1 wire alt and go with 3 wire alt for it to properly work. I have seen this problem before with the 1 wire set-up. And also it could be the alt getting weak also. JMO


Cole
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Old 11-07-2010, 09:26 AM
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Hi Chet, long time... I had major knee surgery after taking a fall while on vacation in August. Finally able to hop around on crutches. Anyways... If I unplug the plug, or disconnect #2 (jumper to the red post) The alternator doesn't charge at all. Therefore, I'm assuming we have a 3 wire alternator? I'm not running an idiot light or anything to the #1 wire, which I thought was only used if your running a idiot light or amp light and this would only come on in the event the alternator doesn't charge? I may be incorrect? Should I hook up an idiot light and would that help. The #2 wire, I was told needs to be put on the red terminal of the alternator as a jumper. Where would be the appropriate place to wire this wire so this alternator will work sufficiently. I think your advise make sense, as usual. I rather have the alternator functioning correctly before installing relays that I may not need.
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Old 11-07-2010, 12:30 PM
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OK, I had a light from an old Harley I had that worked with oil pressure, high beam lights and ignition switch. I connected one side of the wire to the ACC of the ignition switch. The other side went to the #1 terminal on the alternator. We started it up and it appears to work fine. The light went out, etc. The voltage came up right away opposed to having to rev the engine up to activate the alternator. At idle we were just under 14 volts of charge. We hit the headlights on and the voltage dropped to just under 13 volts at idle. Rev ving the engine did change anything. When depressing the brake pedal, were at 12 volts. Not sure if this wiring #1 on the alternator made a difference? We may opt to install on relay temporarily on the low beams just to see if that will make a difference. My buddy has a cool red light mounted to his dash now....

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Old 11-11-2010, 03:12 PM
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UPDATE- We tried to connect a relay to the low beams on my friends car. I couldn't see a difference in brightness with the halogens with a relay or not. We still had the problem with voltage dropping when he put on headlights and brakes. However there was some improvement and it was above 12.5 volts.

I had a similar problem with my truck, I took T buckets advice stating my 3 wire GM alternator wasn't hooked up right. Anyways, I had the 8GA main feed wire connected to the red post on the alternator and a jumper wire from #2 terminal to the same red batt. post. I got around 13.8 volts at idle with fresh battery. With the headlights, it dropped to 13 and sometimes 12.5 volts. I also had to rev the engine to get the alternator to charge (self exciting) 10 SI alternator. I decided to hook up #1 terminal. I used a idiot light I had from an old harley which had no ground and two wires needed. I wired on side to the ignition and the other to #1 terminal. I started it up and I'm reading 14.1 volts, Headlights on - 13.9 volts. WOW... big difference! No having to rev the engine either. The only problem I see is the idiot light is bright with the engine off. When I start it, it doesn't turn off, but is very dim. When I shut the engine off, it's bright again. Maybe I'm using the wrong the idiot light? A big thanks to T bucket on this one. This was bothering for some time. Hopefully this will help others who have the same problem I was experiencing.
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Old 11-11-2010, 04:13 PM
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Quote:
Originally Posted by kleen56
UPDATE- We tried to connect a relay to the low beams on my friends car. I couldn't see a difference in brightness with the halogens with a relay or not. We still had the problem with voltage dropping when he put on headlights and brakes. However there was some improvement and it was above 12.5 volts.

I had a similar problem with my truck, I took T buckets advice stating my 3 wire GM alternator wasn't hooked up right. Anyways, I had the 8GA main feed wire connected to the red post on the alternator and a jumper wire from #2 terminal to the same red batt. post. I got around 13.8 volts at idle with fresh battery. With the headlights, it dropped to 13 and sometimes 12.5 volts. I also had to rev the engine to get the alternator to charge (self exciting) 10 SI alternator. I decided to hook up #1 terminal. I used a idiot light I had from an old harley which had no ground and two wires needed. I wired on side to the ignition and the other to #1 terminal. I started it up and I'm reading 14.1 volts, Headlights on - 13.9 volts. WOW... big difference! No having to rev the engine either. The only problem I see is the idiot light is bright with the engine off. When I start it, it doesn't turn off, but is very dim. When I shut the engine off, it's bright again. Maybe I'm using the wrong the idiot light? A big thanks to T bucket on this one. This was bothering for some time. Hopefully this will help others who have the same problem I was experiencing.
Make sure the light is connected to a switched source, you really need to use the right light as the resistance is different on different bulbs. You can eliminate the light and pick up a resistor to cut into the feed for terminal 1.
Sounds like you are close, good luck resolving the small light issue
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Old 11-11-2010, 05:38 PM
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I think I know what the problem is... The light I'm using from a Harley is a LED type light. I read a regular bulb type without negative ground is to be used. Anyone know where I can purchase this? Or what type of bulb did you use with having to purchase the diode. Diode is used if your not running a light.
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Old 11-12-2010, 07:18 AM
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An LED is a diode, a Light Emitting Diode. You can buy diodes at Radio Shack.
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Old 11-12-2010, 07:29 AM
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Quote:
Originally Posted by kleen56
OK, We may opt to install on relay temporarily on the low beams just to see if that will make a difference.

Just to clarify a relay simply takes the load off the head light switch. In some circuits the relay allows a small voltage/ampere device to control a larger voltage/ampere device. A relay is for isolation not to increase voltage or amperes.

"know what the problem is I'm using from a Harley is a LED type light." exactly gen or alt lights are incandescent, standard 12v bulb,
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