Voltmeter drops severely with headlights on...

ollietonk · 09-22-2009, 04:45 PM

This can't be normal, but anytime I turn the headlights on the voltmeter drops off the scale, below 10V. When the blinkers are on, it sits and ticks with the on/off of the blinker. The lights seem bright enough but I haven't run them that long at once. When I turn them off, the voltmeter immediately returns to a normal reading.

I'm interested in getting a winch and maybe a stereo someday and don't think my electrical system is up to it. (90A alt and optima red top).

What do you guys suggest?

spcmac249 · 09-22-2009, 06:21 PM

check your wiring. the volt meter should be parallel to the rest of the circuit. if it is in series, when you turn on the lights then the voltage will drop at the meter.

**John Strenk** · 09-22-2009, 07:36 PM

Quote:

Originally Posted by spcmac249

check your wiring. the volt meter should be parallel to the rest of the circuit. if it is in series, when you turn on the lights then the voltage will drop at the meter.

It would be pretty hard to wire the volt meter in series and have anything working right.

More likely he has numerous corroded wires and contacts in his wiring harness. The voltmeter is unfortunatly at the end of one of the farthest branches of the harness so any drop previously will have a major effect on the voltmeter.

Time to go thru your harness and freshen up all the connection particually the ground straps and all that jazz. Your harness just might be corroded enough to limit current ot your circuit even though you have a 90 amp alternator. C

Check your voltage across the battery to see if there is any drop there. Then check it at the starter solenoid were the battery connects to one of the big posts. Then check the voltage at the fuse box on one of the hot and one of the switched fuses. Any place you start to see lower voltages, there is a poor connection between the last place you checked and were you're checking at the moment. You can pretty well find out what section opf your harness is bad this way and replace only the bad sections.

My guess is the terminal on the starter solenoide is corroded or your main feed is corroded.

**gojeepin** · 09-22-2009, 07:59 PM

Quote:

Originally Posted by John Strenk

... Time to go thru your harness and freshen up all the connection particually the ground straps and all that jazz. Your harness just might be corroded enough to limit current ot your circuit even though you have a 90 amp alternator...

After Hurricane Isabel's wind driven salt water caused all my electrical system to gradually start failing, I cleaned all my connectors like John said. I also put 2 gauge battery cables and grounding straps on. That made everything work much better. My lights are much brighter too.

carnuck · 09-22-2009, 08:41 PM

Sounds like bad body to motor ground.

wellmax · 09-22-2009, 11:03 PM

1984 CJ-7 with 4 banger:

my volt meter will go down some when lights are on.

i have a Ramsey rep 8000 winch and when it kicks on the volt meter will drop .

I have a 1000 cold cranking amp battery in the jeep, biggest battery i could find that would fit in battery box.

also i try to increase my rpms when making a pull, to help the charging system.

I have only used the winch about 10 times and it has worked well each time. But I have not had to make repeated long hard full length cable pulls.

spcmac249 · 09-23-2009, 05:25 AM

Did you check the voltage regulator?

73jeep · 09-23-2009, 09:05 AM

Quote:

Originally Posted by wellmax

i have a Ramsey rep 8000 winch and when it kicks on the volt meter will drop

Yeah thats normal. Winch motors draw anywere between 50-400 amps that will drop your voltage.

73jeep · 09-23-2009, 09:09 AM

EVERY cj owner should be taking the the wiring appart and checking EVERY connection for corrision or heat damage from high resistance connections. It is very easy to melt some of the plastic plugs in the system. Clean them up and reassemble with dielectric grease.

Corrosion =high resistance= heat = FIRE watch out guys.....

ollietonk · 10-02-2009, 06:32 PM

I'm off this weekend and will look into all these possibilities. Thanks and I'll let you know what I find

red mistress · 10-02-2009, 07:01 PM

The factory volt meter will do exactly what you are describing.

Even when the CJ was brand new, the volt meter would abnormally drop when anything was turned on.
Or even see more Amps when heavy draw.

Getting the CJ repaired under factory warranty, (12 months or 12,000 miles...LOL.) it would sometimes take dealership several different volt meters installed to find a good one.

I've got nice used Voltmeter that I pulled out of a Jeep before I sold it, I know for sure it works correctly. 25 shipped. PM if interested.

**JeepHammer** · 10-02-2009, 10:34 PM

What's happening is,
Your fuse block is supplied with a 10 Ga. wire.
From there, that supply is split off into all your accessories and loads.

Like of like taking a small diameter garden hose, then punching holes in it...
Each hole leaks some of the Pressure/Volume (Voltage is analogous to 'Line Pressure').

Your Volt Meter is on the end of that hose and reads as the different 'Holes' or Electrical Loads take their share out of the supply line.
That's why you see your volt meter move with the flashers or turns signals,
And see it drop when you turn the head lights on.

Now, you can EASILY take your headlights off the main Fuse Block circuit by adding Power Relays and a heavy power feed to the head lights.
This will also take the load off the headlight switch and make it last longer.

You can hook up all the accessories you want to, just use power relays to feed them so you don't draw too much on the dinky little fuse block the CJs came with.

As for a winch,
You really should install TWO batteries before you install a winch.
Winches draw MUCH MORE power than your engine starter,
And they usually draw that power for longer than your starter.

So trying to run a winch with just one small battery is a good way to starve the winch for Electrical Current, and that can actually case damage to the winch and battery.

By doubling the battery capacity, you also double the supply to the winch, and you double the ability of the batteries to recover after you do a hard pull with the winch.

Remember, there is no way to supply enough current to the winch with an alternator.
Most alternators aren't capable of more than about 60 Amps for more than a few seconds (no matter what the 'Zuper Duper' alternator sellers say),
So for very large loads,
Winches, Engine Starters, Huge Stereos, Inverters, Welding, Ect.
You REALLY need extra battery capacity to fill in for what the alternator can't produce.

HOW you wire the batteries is as important as using a second battery.
Most wiring arrangements limit the amount of current supplied to the winch/inverter/ect. and that is a BAD THING!
You want to wire so BOTH batteries get free current flow to the Winch (Or Whatever) so the load doesn't starve and overheat...

There are several articles on the forum about putting headlights, driving lights, and other loads on relays so you can take that load off the fuse block and factory wiring harness.

There are also articles on dual batteries, what wiring for what application, and how to do things.

Do you have any specific projects in mind, or is this general questioning to get you up to speed on the subject?