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Author
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Topic: chasing electrical gremlin
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craigber
Gearhead Posts: 125
From: Vancouver, Canada
Registered: Sep 2000
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posted 10-26-2005 10:02 PM
   
hi...hit brakes and all lights work BUT one bulb is dimmer....turn on running lights and all work (same intensity)....hit brakes and the same weird bulb goes OUT! release brake and running lights are all back (same intensity)...what the #ell is going on here? checked socket with ohm meter and seems ok....just replace alternator, dimmer switch and headlight switch....is my new headlight switch wonky?
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mustangboy
Gearhead Posts: 1198
From: Ont, Canada
Registered: Mar 2002
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posted 10-26-2005 10:08 PM
Can you be more specific as to which bulb is giving you the trouble.I'm assuming you mean a tail light bulb since you mentioned brake lights?It sounds like it could be a bad ground to me.They can cause some very strange problems as the light will ground itself through other circuits.Have you tried a different bulb? ------------------
68 J-Code,Sprint,306 4 speed,4.11s 13.69@101...............
66 coupe 289 4 speed, 3.20 cruiser http://mustangsandmore.50megs.com/MembersPics/mustangboy.html http://mustangsandmore.50megs.com/MembersPics/mustangboy2.html
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68mustang351w
Gearhead Posts: 486
From: San Diego, Ca
Registered: Sep 2004
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posted 10-26-2005 10:38 PM
Try a different bulb and make sure you insert it correctly. There are two posts and they are slightly offset, there only one right way to put it one... David F.
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stc65coupe351w
Gearhead Posts: 678
From: Moreno Valley, California
Registered: Sep 2004
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posted 10-27-2005 12:19 AM
I had sort of a similar problem with my brake lights. Found it to actually the turn signal switch. I had replaced the return cam and it did not work well with the switch so I ended up changing the entire unit. That was on a 65.------------------
-351w Bored .30-351w Heads Fully Ported
-Custom made Ford 9" 3.70
Pics Michael
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craigber
Gearhead Posts: 125
From: Vancouver, Canada
Registered: Sep 2000
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posted 10-27-2005 12:56 AM
Hithe bulb is ok as switching one of the bright ones with the dim one doesn't solve the problem...it is the outside left driver side taillight...i tested the sockets and found the dim bulb one has a bit more resistance but only about 10% or so....i assume the ground is the same for all functions (turn signal...running light....brake light) so if ground works for two it should work for the third...or can a bad ground increase resistance in the circuit under higher load such as when running lights are on and then brakes applied ...just can't understand why bulb goes out just because headlights are on....i appreciate everyones help...electrical is the worst
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Scott H
Gearhead Posts: 1038
From: Chicago area
Registered: Mar 2005
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posted 10-27-2005 07:07 AM
Try the multi-function switch in the steering column. It has power passing thru it for turn signals and brakes. Could be a bad contact or a minor short inside. Its the only other part they all have in common, and they are known to cause problems like you are having.
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68F100
Gearhead Posts: 2778
From: Burlington, Iowa
Registered: Oct 99
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posted 10-27-2005 05:54 PM
I would look for a loose ground on the dim light also. My escort had some weird things going on with it. Pass side taillight was dim till you hit the brakes. Then it would go out and the reverse lights would come on. It was a bad ground. Couldn't tell until I squirreled my way into the hatch and saw one wire was just barely loose from the connection. Stuck it back in and it worked fine.
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mustangs68
Moderator Posts: 25842
From: Buckroe Beach Va MCA#39406 M&M #12 Member Mustang Club of Tidewater
Registered: May 99
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posted 10-27-2005 06:29 PM
BTW what year?
68 famous for bad grounds and corrosion in the sockets.
Sam
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