# Strange Voltage Drop **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** cherokee, jeep\ **Created:** [May 24, 2010, 11:52pm UTC](https://community.cartalk.com/t/strange-voltage-drop/49338 "2010-05-24T23:52:27Z")\ **Posts on this page:** 18\ **Page:** 2
**Author:** ![Steve\_Heather](https://avatars.discourse-cdn.com/v4/letter/s/43a26b/32.png) [@Steve\_Heather](https://community.cartalk.com/u/Steve_Heather)\ **Post date:** [May 25, 2010, 9:56pm UTC](https://community.cartalk.com/t/strange-voltage-drop/49338/21 "2010-05-25T21:56:50Z")
Thank you. Not directly. Dumb… I should have done that at the beginning… ---
**Author:** ![waterboy](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/waterboy/32/764_2.png) [@waterboy](https://community.cartalk.com/u/waterboy)\ **Post date:** [May 25, 2010, 11:01pm UTC](https://community.cartalk.com/t/strange-voltage-drop/49338/22 "2010-05-25T23:01:31Z")
Just to clarify, your alternator is putting out 14.2 volts. When not in drive, 12.5 volts is your reading, when driving 9 to 10 volts. If your car voltmeter is correct you are loosing almost 2 volts at idle and 5 volts while driving. That is a pretty big load. It is apparent not enough energy is getting to the battery and ignition system. The alternator is good, the battery is good. Check all the cables and connections. ---
**Author:** ![vtcodger2](https://avatars.discourse-cdn.com/v4/letter/v/e68b1a/32.png) [@vtcodger2](https://community.cartalk.com/u/vtcodger2)\ **Post date:** [May 26, 2010, 3:57am UTC](https://community.cartalk.com/t/strange-voltage-drop/49338/23 "2010-05-26T03:57:32Z")
Well, yeah. But you’ve eliminated the easy stuff like poor battery connections and defective battery cables. Seems like the next thing you need to know is whether the meter on the dash is giving you accurate readings for the whole electrical system, or maybe much of the car is running fine, but the dash meter is attached to a subsystem that has low voltage for some reason. Offhand I don’t think 9.5volts sustained at the positive battery terminal – if that is the case – could possibly be caused by anything other than a defective battery or a defective charging system. But maybe I’m not thinking clearly. ---
**Author:** ![Steve\_Heather](https://avatars.discourse-cdn.com/v4/letter/s/43a26b/32.png) [@Steve\_Heather](https://community.cartalk.com/u/Steve_Heather)\ **Post date:** [May 26, 2010, 10:27pm UTC](https://community.cartalk.com/t/strange-voltage-drop/49338/24 "2010-05-26T22:27:36Z")
Thanks, Yes The voltage at the alternator and battery is 14+ loaded or unloaded. I replaced the both the positive and negative wires. It is ABSOLUTELY tied to movement. RPM has no effect. Being in Drive or Park has no effect. ---
**Author:** ![Cougar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/cougar/32/21348_2.png) [@Cougar](https://community.cartalk.com/u/Cougar)\ **Post date:** [May 27, 2010, 9:48am UTC](https://community.cartalk.com/t/strange-voltage-drop/49338/25 "2010-05-27T09:48:39Z")
To see if there is a problem in the bus wire between the battery and the main power panel under the hood try running a temporary jumper wire between the positive battery post and the main fuse in the fuse panel. Be careful not to short the wire to any ground point if you do this. If the trouble still occurs then you may need to bypass the wiring between the panel under the hood and the dash fuse panel. ---
**Author:** ![vtcodger2](https://avatars.discourse-cdn.com/v4/letter/v/e68b1a/32.png) [@vtcodger2](https://community.cartalk.com/u/vtcodger2)\ **Post date:** [May 27, 2010, 1:11pm UTC](https://community.cartalk.com/t/strange-voltage-drop/49338/26 "2010-05-27T13:11:05Z")
This is an important point. In order to pull a healthy battery down to 9.5 volts output via a short circuit, you’d need a really substantial current drain. I’m guessing 100 amps or more. It’s hard to believe that wouldn’t lead to smoke and flames in not much time at all. ---
**Author:** ![Cougar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/cougar/32/21348_2.png) [@Cougar](https://community.cartalk.com/u/Cougar)\ **Post date:** [May 27, 2010, 2:55pm UTC](https://community.cartalk.com/t/strange-voltage-drop/49338/27 "2010-05-27T14:55:21Z")
I agree. The trouble isn’t due to a short, it is due to a bad connection between the battery and the accessories power bus, which is a different area than the charging system and that area is ok. ---
**Author:** ![Steve\_Heather](https://avatars.discourse-cdn.com/v4/letter/s/43a26b/32.png) [@Steve\_Heather](https://community.cartalk.com/u/Steve_Heather)\ **Post date:** [May 27, 2010, 7:26pm UTC](https://community.cartalk.com/t/strange-voltage-drop/49338/28 "2010-05-27T19:26:06Z")
Thank you, interesting… I will check it out and post the results after 5pm PST ---
**Author:** ![tardis](https://avatars.discourse-cdn.com/v4/letter/t/f0a364/32.png) [@tardis](https://community.cartalk.com/u/tardis)\ **Post date:** [May 27, 2010, 9:56pm UTC](https://community.cartalk.com/t/strange-voltage-drop/49338/29 "2010-05-27T21:56:04Z")
I have found that many posters don’t really know what “short circuit” means. They just use the word short to cover any sort of electrical problem. This isn’t a short circuit issue. ---
**Author:** ![Steve\_Heather](https://avatars.discourse-cdn.com/v4/letter/s/43a26b/32.png) [@Steve\_Heather](https://community.cartalk.com/u/Steve_Heather)\ **Post date:** [May 27, 2010, 11:15pm UTC](https://community.cartalk.com/t/strange-voltage-drop/49338/30 "2010-05-27T23:15:50Z")
Actually, in this case we are assuming it is an Open, or at lease a partial open. ---
**Author:** ![Cougar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/cougar/32/21348_2.png) [@Cougar](https://community.cartalk.com/u/Cougar)\ **Post date:** [May 27, 2010, 11:43pm UTC](https://community.cartalk.com/t/strange-voltage-drop/49338/31 "2010-05-27T23:43:28Z")
What it is called is a bad connection, which causes a voltage drop across it and so less power gets to the actual load. ---
**Author:** ![Serpentstooth](https://avatars.discourse-cdn.com/v4/letter/s/a6a055/32.png) [@Serpentstooth](https://community.cartalk.com/u/Serpentstooth)\ **Post date:** [May 28, 2010, 3:23am UTC](https://community.cartalk.com/t/strange-voltage-drop/49338/32 "2010-05-28T03:23:32Z")
Hi! Check all fusible links also and check ground strap from engine to firewall!! ---
**Author:** ![oldwrench](https://avatars.discourse-cdn.com/v4/letter/o/90ced4/32.png) [@oldwrench](https://community.cartalk.com/u/oldwrench)\ **Post date:** [May 28, 2010, 9:17pm UTC](https://community.cartalk.com/t/strange-voltage-drop/49338/33 "2010-05-28T21:17:17Z")
Eliminate your dash gauge first by hooking up your jumper leads to a good ground and the B positive post on the alternator. Run the leads into the vehicle{out the hood by the windshield into the passenger window} and hook them up to your VOM meter. Have Heather read the VOM and see if it corresponds to your dash gauge as you drive the vehicle. ---
**Author:** ![Steve\_Heather](https://avatars.discourse-cdn.com/v4/letter/s/43a26b/32.png) [@Steve\_Heather](https://community.cartalk.com/u/Steve_Heather)\ **Post date:** [May 28, 2010, 11:06pm UTC](https://community.cartalk.com/t/strange-voltage-drop/49338/34 "2010-05-28T23:06:19Z")
Thanks… Very clever… so, it finally stopped raining (here in Calif)… I finally get to go check the wiring. Start with the ground. Look for the strap… Found the half that was on the body… Getting a new one now… Steve ---
**Author:** ![Steve\_Heather](https://avatars.discourse-cdn.com/v4/letter/s/43a26b/32.png) [@Steve\_Heather](https://community.cartalk.com/u/Steve_Heather)\ **Post date:** [May 31, 2010, 10:31pm UTC](https://community.cartalk.com/t/strange-voltage-drop/49338/35 "2010-05-31T22:31:33Z")
RESOLVED!!! It was the ground strap. It looked like it was there until you actually tried to follow it. the last 4" were missing. A $15 part and 5 minutes to mount it. Started it up and the gauge immediately hit 14v. I turned on everything i could and the voltage would not drop below 12…!!! I started rolling and no change at all!!! Thank you all for your help. Sorry it was something so basic. I will remember to do more investigative work next time. ---
**Author:** ![Cougar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/cougar/32/21348_2.png) [@Cougar](https://community.cartalk.com/u/Cougar)\ **Post date:** [May 31, 2010, 10:41pm UTC](https://community.cartalk.com/t/strange-voltage-drop/49338/36 "2010-05-31T22:41:42Z")
Glad you found the problem and thanks for the update. ---
**Author:** ![markkw](https://avatars.discourse-cdn.com/v4/letter/m/4491bb/32.png) [@markkw](https://community.cartalk.com/u/markkw)\ **Post date:** [June 1, 2010, 1:56am UTC](https://community.cartalk.com/t/strange-voltage-drop/49338/37 "2010-06-01T01:56:31Z")
Steve, Sorry for taking a while to get back to this … by “load” I mean “electrical load” not mechanical load on the engine in my previous comment. Okay, with the additional info here I’m going to suggest a few more possibilities … first is if the lights are not dimming, wipers/fan not slowing when the dash meter is showing a low voltage reading then the voltage is not actually dropping. You said above you read 14+ volts loaded or unloaded - was the dash mounted meter showing some lower reading at the same time? Given that the oil pressure gauge is possibly responding to changes in the electrical load, it’s starting to sound to me like you may have an issue with a high-resistance ground in the dash panel circuit (again, that providing the actual alternator output is not changing when the dash mounted meter is saying something else. Bad/missing grounds in a DC system can cause all kinds of wierd things to happen and depending on how the circuitry is set-up, a bad ground in the dash circuit may in fact cause the alternator output to drop off. Hate to say it but I’d suggest ripping out the dash and going through all the plug connections and ground connections. Even if they “look” good, disconnect each one (one at a time whenever possible) checking to make sure all the pins/fingers are properly locked into the plug body and that there’s no corrosion, signs of arcing or anything that obviously looks bad/wrong. For the ground connections (usually an eye terminal on a screw into the dashboard supports or a body panel, remove the screw and clean everything especially the underside of the screw head and the surface of the metal where the terminal eye is trying to make contact. You would be surprised at just how little corrosion is necessary to increase the resistance of a ground that reasults in all kinds of crazy things to happen. I highly doubt your problem is going to extend beyond the dash area - this could be something as simple as a plug that’s loose so you may want to get a good light and contort yourself into positions the human body was never intended to be in without breaking bones and just have a look-see up under the dash before pulling it out. ---
**Author:** ![tardis](https://avatars.discourse-cdn.com/v4/letter/t/f0a364/32.png) [@tardis](https://community.cartalk.com/u/tardis)\ **Post date:** [June 1, 2010, 2:06am UTC](https://community.cartalk.com/t/strange-voltage-drop/49338/38 "2010-06-01T02:06:33Z")
You know, if you’d read a little further down, you’d see that the OP has solved the problem. It was the ground strap from the engine to the body after all. [Previous page](https://community.cartalk.com/t/strange-voltage-drop/49338.md?page=1)