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brake lights 79' f350 please help
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tusseltussel
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Mar 13, 2009, 11:34 AM
Post #1 of 11
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brake lights 79' f350 please help
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hello, im having trouble here.
1979 ford f350 351m
no break lights
ive gone alond from back to front all wiring looks good and tight, i checked with a volt meter at the connections by the tail lights and the harness under the hood, no power. i went under the dash and jumped the switch behind the brake pedal.... no power, no light.... when checking the wires i couldn't see where anyone did any creative wiring, no inline fuses... .the fuse pannel in the truck is worn and cannot tell if there is a fuse for the brake lights but at a quick look all fuses look good im not sure where to go from here anyone got any ideas?????
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Mar 13, 2009, 11:48 AM
Post #2 of 11
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Re: brake lights 79' f350 please help
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There needs to be power at the switch at the brake pedal all the time. Test all the fuses if need be with a test light. If this still uses glass fuses sometimes they look ok and aren't more than the newer types. Roll them or just remove replace can help or the fuse could be bad. You should be able to find which fuse is for brake lights as it's empowered all the time - most are not,
T
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tusseltussel
User
Mar 13, 2009, 12:25 PM
Post #4 of 11
(1454 views)
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Re: brake lights 79' f350 please help
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thanks for the repl tom.....
i just went out and found that i do have power to the one side of the switch behind the pedal and the fuse is ok... i noticed that when i push the pedal down(release the switch) that wire looses power and there is no power to either of the 2 wires on that switch so this leads me to belive its a short sumwhere.. and when those wires are jumped together still nothing so is it a short i should be looking for?????
couldnt get it to post with the quote
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Mar 13, 2009, 12:54 PM
Post #5 of 11
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Re: brake lights 79' f350 please help
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Hmmm? A plain short should blow the fuse. Since you don't detect power when the live (you checked) switch is jumped then the power to that is just a hair of power - not the amount it needs and the draw of the lights is taking it down and or creating an "open" at a weak spot along the source of power.
Perhaps make up a fused jumper wire and empower the wiring to that switch separately for a test. They sell "fuse in line" wire and you can put clips or what you like on ends - just work with fuses hot wire if you do that.
The spade holder type is easier to deal with than the glass ones IMO,
T
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tusseltussel
User
Mar 13, 2009, 4:28 PM
Post #6 of 11
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Re: brake lights 79' f350 please help
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strange thing... hot wire to switch 4 volts, i jumped a wire from the fuse to the switch and disconnected the 4 v line.. lights work switch works wires don't get hot... old 4v wire reads 10 now???? i check it a few min. later and is back at 4 ???? i dnt know whats up, a short sumwhere between the fuse and the switch i guess if i dissconnect the old wire and just run a separate new one, the turn signals still work so every thing from the turnsignal switch back is good. the switch is new the old one would short out and than no break lights
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Loren Champlain Sr
Veteran
/ Moderator
Mar 13, 2009, 4:37 PM
Post #7 of 11
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Re: brake lights 79' f350 please help
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If memory serves, and it usually doesn't, seems that the brake lamps ran through the turn signal switch on the earlier Fords? Wouldn't want a short in the column.
Loren
SW Washington
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Mar 13, 2009, 4:48 PM
Post #8 of 11
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Re: brake lights 79' f350 please help
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I can't figure out the 4v reading for anything in the 70s! Same switch idea has been used since forever and virtually all failures were the plug and wires - a couple the switch itself. Can't understand if it shorted even partially that it wouldn't blow a fuse??
T
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Loren Champlain Sr
Veteran
/ Moderator
Mar 13, 2009, 5:09 PM
Post #9 of 11
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Re: brake lights 79' f350 please help
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>> if it shorted even partially that it wouldn't blow a fuse?? << Uh, partial short?  I said that I wasn't an electrician! LOL.
Loren
SW Washington
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Mar 13, 2009, 5:12 PM
Post #10 of 11
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Re: brake lights 79' f350 please help
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What I meant is like insulation bared to draw off some current but still making 4v doesn't make sense to me??
T
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tusseltussel
User
Mar 14, 2009, 5:35 AM
Post #11 of 11
(1426 views)
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Re: brake lights 79' f350 please help
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your memory is correct but as i said the turnsignals work so power is getting back there, they are powered from there own 12v line though, thats why they still work, power to the switch stops until the pedal is pushed down. i found that the short was between the fuse and the switch, before it goes to the turnsignal hense the 12v power supply only getting 4 v so im gonna take the fuse out disconnect that wire if i can and just run a new 12v wire with its own fuse so that old wire will no longer be shorting out or whatever is goin on, it will be dead no power and the power to the switch will come from the new wire.... sounds good to me thanks for helpin me out guys
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