Only getting 3 vdc to tail light ?

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Model T Ford Forum: Forum 2015: Only getting 3 vdc to tail light ?
Top of pagePrevious messageNext messageBottom of page Link to this message  By Travis Melnick -Waterford , Pa on Thursday, October 15, 2015 - 09:40 pm:

Hey guys ,
Hershey was awesome , next year I'm going to get there on Monday so I can start shopping the flea on Tuesday , I got there on Thursday at around 9:30 due to Harrisburg rush hour traffic , was not disappointed in anyway , but wished I'd been there earlier in both day and hour , anyhow , picked up a few parts for the Tudor and ordered a couple 6v tail light bulbs from langs as they were sold out , they came in today so I put one in the socket and no light ? Checked with my meter and I'm only getting 3 volts ?? New wiring and headlights work fine , checked connections , 6v at switch but 3 at lamp ?? What am I missing ?? ( other than 3 volts :-) )


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Thursday, October 15, 2015 - 10:54 pm:

Assuming you have the tail lite wire connected to the "tail lite" terminal on the ignition switch, My guess is that you probably don't have a good ground at the rear of the car since there are a lot of painted connections in the ground path. If that isn't it then tell us the year of the car so we can tell you how to do a point by point testing. If you are indeed getting 3 V then the bulb should at least glow a bit. Are you sure it isn't lit at all?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Paul Mikeska, Denver CO on Thursday, October 15, 2015 - 10:57 pm:

Travis,

My first thought is that the tail light has a bad ground connection. Check the voltage from the hot wire on the tail light directly to the battery negative terminal. If you see 6 volts then the ground connection to the tail light is bad.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Paul Mikeska, Denver CO on Thursday, October 15, 2015 - 10:59 pm:

Hmmm. John posted faster than I did!

(Message edited by paulmikeska on October 15, 2015)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Wayne Sheldon, Grass Valley, CA on Friday, October 16, 2015 - 02:45 am:

The other possibility is that the wire in the car could be too small? Six volt electrical requires a larger gauge wire than twelve volt does. The longer the wire if it is too small? The greater the voltage drop. I have seen 14 and even 16 gauge wire on antiques. That will not work on a 6V tail-lamp because of the length, but might work on the headlamps. Someone please correct me here? I believe that 12 gauge is recommended for six volt automotive lamps. But I often use 10 gauge, especially on tail-lamps.
John R and Paul M are both probably right. A bad ground path is very likely. On a typical antique? There are between six and a dozen points where the ground path can fail. You need to find any and all of them. Ground faults are a cumulative failure and react to not only voltage, but current and load.
Drive carefully, and enjoy, W2


Top of pagePrevious messageNext messageBottom of page Link to this message  By keith g barrier Savannah Tn. on Friday, October 16, 2015 - 07:25 am:

I used #12 wire on all my lights with a dedicated ground for the lights, bright and no more problems. KGB


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