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John R. Hess

DIM TURN SIGNALS

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I am having an issue with my turn signal operation of my all stock (6 volt) 1955 Thunderbird.
 
I've had the car for 22 years and the turn signals worked perfectly in the past.  The deterioration I'm experiencing happened over the last 2 years.  It was very gradual so I didn't notice it until it became cronic.
 
The issue is the turn signals burn so dim that, even at night, you can barely see them.  It affects the front lights, the rear lights and the dash indicators.  I have collected the data on it's current operation:
 
The battery voltage ias 5.97 volts (motor off, ignition switch on).  At the rear socket, for reference, with no bulb installed, the parking lights are 5.6 volts (both sides same).  When you hit the brake light, the voltage available in socket is 5.94 volts, yielding a normal brake light (agan, both sides same).  Now to the turn signal.  I measured the voltage on the wire feeding the flasher and there is 5.74 volts there.  To make the bulbs stay on, I put a jumper wire across the flasher, sending the 5.74 volts to the turn signal switch.  When selecting either side, both left and right measure 4.1 volts.  Now we know why they are dim.  The interesting thing when you put the rear bulb in it's socket and watch the front turn signal or the dash indicator,  the brightness drops quite a bit, indicating the voltage must fall below 4 volts when the load of the bulb is added
 
Some times, the flasher does flash.  Other times, it does not.  Nothing consistent.
 
Question is:  Any idea what would cause both sides to have only 4.1 volts at the socket in the rear?  It's not like one side is higher or lower than the other...they are almost perfect at 4.1 volts each.  Have you ever experienced or heard of anyone with this issue?    Can you suggest any further voltage measurements that may be useful.  I have all the manuals for the car (shop and electrical) and they offer no troubleshooting help beyond what I've done.  For the record, both tail lamp bulbs are correct.
 
I have a feeling the problem is something relatively simple.
 
Thanks much for your help
John Hess
York, Pa.

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Try measuring back at the flasher jumper wire with a signal on and the bulb in. Does it drop to 4.1v back at the jumper wire too?

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Check all the sockets for rust or corrosion.  Also check the mounting for the various lights to make sure the grounds are good.  The parking lights and the rear lights are self grounded (no separate ground). 

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The way most cars are wired the front turn and indicators use the same circuit. The rears to keep from back feeding the fronts and causing the fronts to also light with the brake pedal pressed are run separately. Since the brake lights and turn lights are the same bulb.I would suspect the turn signal switch. I would disconnect the wires from the switch and send power to each bulb from that point. If they are bright then you have a bad switch. If they are dim I would trace the wires back.

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Thanks to all for your suggestions.  I should have pointed out that the grounds are good and, just in case,  I even went so far as to run a #12 wire from the ground terminal on the battery to the taillight assembly and grounded it there....no change.  Inside the sockets look like brand new.  All wiring is in excellent condition. 

 

The voltage remains constant at almost 6 volts on the blue wire at the flasher, whether the bulb is in circuit or removed.

 

I am inclined to think there is something going on with the turn signal switch, since that's where the switching goes on.  The brake lights go thru there, as do the turn signals, being selected by the switch when making a turn.  Since the brake lights are normal and the turn signals low, it sure looks like something is going on there with the turn signal portion of the switch.

 

Thanks to all. All suggestions were very valid and helpful.   This is where I am now.....the trouble shooting will continue.

 

John

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