Electrical question

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Model T Ford Forum: Forum 2016: Electrical question
Top of pagePrevious messageNext messageBottom of page Link to this message  By dennis delano on Sunday, July 03, 2016 - 12:18 am:

Hello all, I am finally getting my '26 touring back together after replacing the ring gear and switching back to 6 volts, all appears to be working ok but I noticed that when I switch on the headlights, the ammeter immediately pegs out in the down position with the needle buried, but the headlights (both dim and bright) work seem to work fine. It will do this whether the car is running or not. I am assuming that I have a direct short somewhere, but was wondering if anyone can give me a clue as to where to start looking. I would have thought if there was a direct short that the headlight bulbs would blow out? thank's


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Sunday, July 03, 2016 - 01:28 am:

My first suggestion would be try a different meter then start checking the light wiring for shorts. Old or new wiring?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kevin Whelihan Danbury, WI on Sunday, July 03, 2016 - 05:47 am:

Remember, that you have a tail light on a '26 in the mix too. I would start disconnecting leads for the various loads and see if that makes a difference, then look for worn wiring harnesses, corrosion, and maybe look at the Ammeter. The Improved Car ammeters are notoriously inaccurate.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Trent Boggess on Sunday, July 03, 2016 - 06:27 am:

Hi Dennis,

Pegging the amp meter when you switch on the headlights but the car is not running is typical for a Model T. The headlights draw quite a bit of current, and the amp meter is reflecting that.

What should be of concern is if it does that when the car is running. In that case, the generator may not be set correctly, or it may not be charging at all. Assuming you are using a standard Ford cutout, when the car is running the amp meter should show an output of about 6-9 amps. Then when you turn on the headlights, the amp meter reading should drop to zero to a negative 2 or 3 amps. If the generator and cutout are operating properly, turning on the headlights should not peg the amp meter in the negative zone.

Respectfully submitted,

Trent Boggess


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Zibell, Huntsville, AL on Sunday, July 03, 2016 - 10:46 am:

Something to remember with the 26/27 ammeters, especially the reproduction ones is they are not accurate. When you do set the third brush, I wouldn't trust the ammeter but use a more reliable one (such as the ones Fun Projects makes for older cars) or a good multi meter that can handle the current in line with the generator.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Charlie B actually in Toms River N.J. on Sunday, July 03, 2016 - 11:00 am:

You have a short circuit as you suspect. There's no "probably" as it could be in the head lights or the tail light wiring. Inspect/trace all as there's not much to look at. Be suspect of any clips under the car securing the tail light wire to metal parts. If you find nothing pull the tail lamp bulb and see what happens. If you're familiar with wiring you can also disconnect wires at the terminal block until the short is found. it's also possible the ign/light switch is ng.


Top of pagePrevious messageNext messageBottom of page Link to this message  By dennis delano on Sunday, July 03, 2016 - 11:58 am:

OK Thank's, I'll try and trace the wires and find the short, I did notice that that when I had the ammeter and ignition out that the back of the ignition switch was getting warm, but did not notice the gauge pegging out until after I had reinstalled it. I replaced the harness from the ignition switch to the terminal block (the terminal block is new also) so I must have screwed something up! thank's


Top of pagePrevious messageNext messageBottom of page Link to this message  By Peter Claverie, Memphis TN on Sunday, July 03, 2016 - 06:38 pm:

"I must have screwed something up." Well, you may have screwed something down a bit too much. What I mean is, you could have one of the terminal screws in the new terminal block a bit too long, and it's touching metal beneath the block.

Generally speaking, if there's a short there will be heat. Lots and lots of heat. The kind that burns up wires. If you don't have that, you probably don't have a short but have an over-sensitive ammeter.

The easy way is to turn the lights on for maybe 15 seconds, then off, and go around and feel wires and terminals. When you find a hot one, trace it forward - not back, and see where the short is.


Top of pagePrevious messageNext messageBottom of page Link to this message  By dennis delano on Wednesday, July 06, 2016 - 12:47 pm:

Update; I re traced all of the wiring and found that when I screwed the thimble onto the passenger side headlight, I must have twisted the ends of the wire where they enter the bulb contacts and it was just enough to be touching one another,it was a pain to trace because I think it is the original wiring and when I removed the cloth covering,the color coding was so faded that I could not decipher them so I used the continuity tester to make sure I had the right wires going to the right terminals and spotted the twist! The ammeter is not "pegging out anymore and is only showing a discharge which looks ok now, thank's!


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