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TR2/3/3A Another turn signal problem

BobbyO

Jedi Hopeful
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The electrical gremlins strike again, but this one has me totally baffled. Not hard to do at this age. Anyway, while out yesterday with a friend trailing he noticed my right rear turn signal wasn't working. I was getting a good indication on the inside and when I checked, the front was working but the rear, not. I immediately thought it could be the bulb but when I checked it it was OK. Even replaced it with two additional bulbs with the same result. I checked the voltage in the rear socket and had 10.52 volts varying all over the place with the front bulb flashing. I then removed the front bulb and checked voltage, 11.95v at front and 11.58v at the rear. Engine off so this was being supplied by the battery. With front bulb removed, installed rear bulb and it would not flash. I don't understand how I can have near identical voltage with both bulbs removed yet only one flashes when they are installed. Any ideas as to what to look for would be a great help.
 
When you checked the voltage at the rear, was the bulb installed? Where exactly did you check?

Probably a high resistance connection, most likely the ground between the lampholder and body. So check with the bulb in and as close to the bulb as you can get. Then work outward until you find power again.

I've had enough trouble with the rear lamps over the years that I finally made up a ground harness for them. Daisy-chain a black wire from each lamp, and lead it around to one of the fuel tank mounting bolts (along with a ground wire for the fuel sender). Now the only time I have ground problems in the back is when the bulb doesn't make good contact to the socket.
 
I don't understand how I can have near identical voltage with both bulbs removed yet only one flashes when they are installed. Any ideas as to what to look for would be a great help.

Also remember, if you have an original style flasher (not electronic), the current flowing is relative to the speed of the flash. So, the same bulb that caused a "flash" in the front, may not in the rear, because the rear is not drawing enough current, because of the poor (or missing) ground -that would show a normal voltage.
 
Hello Bob

A quick check to see if it is a ground problem. Clip a wire long enough to reach from the battery to the flasher to the battery ground and take the other end and make contact with the bulb holder ground. Be careful do not touch the live side.
If it flashes you have a ground problem.

When I get to the wiring part of the project I think I will do as Randall suggests with a ground wire.

David
 
Thanks all for the help. It was a high resistance connection but not a grounding problem. I had already taken Randall's suggestion and made a grounding harness for all the rear lamps. I had also run a jumper wire from the battery ground to the bulb ground. No change. The problem connection was the green/white wire going in the double connector on the driver's side, engine compartment. It apparently corroded enough to supply power when there was no load (bulb removed) but wouldn't supply enough to flash the bulb. After I cleaned the connection it solved the problem. All turn signals are working again. At least until the next gremlin shows up.
 
That's interesting...reminds me of an old accident we studied in aircraft accident investigation school.

An F84 was being flown by a brand new pilot when the front wheel cocked 90 degrees after take off. Normally, an experienced pilot would fly the jet right back to the runway, since the problem was normally a broken centering spring...and once the wheel touched back down it would center itself. BUT, occasionally the wheel would not center, so the pilot would have to stop the jet with no front wheel steering control, at the risk of rolling the plane over on it's back.

This was in the 1960's, and the F84 was already way obsolete by then...so the decision was made that the plane was worth less than the cost of a pilot, so they decided to fly the plane to a controlled ejection sight and let the rookie shut it down and then bail out, using the nylon (parachute) let down. Well, since he had just taken off and had plenty of gas, they took over 30 minutes, making sure he removed all his loose gear, stowed anything else, and fully went through all the checklists. He then popped the canopy...not off, but open. For some unknown reason the F84 canopy was made to raise in flight, but it would not pop off until AFTER the ejection handles were pulled. So, rookie pulled the handles for the ejection.

What happened is the rookie's seat started up the rails, but the canopy explosive squibs never fired. Had it been closed, the seat would have punched right through the plexiglass, but, being open, the rookies head went right through the front canopy metal rail...knocking him unconscious. Since the F84 used a first generation ejection seat, there was no automatic deployment of his chute, so he...and the seat...rode it into the desert together. Of course he died.

I know...what's this got to do with Bobby's weak connection?!? Well, in the investigation it was found that more than a decade prior, during manufacture of the plane, some line worker had installed the connector for the canopy squibs using 2 male connectors. So, the male prongs touched each other, and for every monthly test for over a decade, the connector showed that it passed excellent voltage through it. It checked good during hundreds of tests. But, when the high amperage passed through the mis-fit connector when it was really needed to save a Pilot's life, it could not transfer enough juice to fire the explosive canopy squibs!

The school used this sad case to show how every accident is a chain of events...all of which have to align perfectly for an accident to happen. In this case...a designer designed a connector that would allow a male to male to fit together...it was then actually mis-fit together, only once in the entire F84 production (they inspected all planes after the incident to know)...a chance spring failure on the nose wheel occurred during a flight with a rookie pilot....the decision was made to open the canopy before the ejection...and, well, it cost a rookie his life.

Oh...what happened to the plane after the ejection? Well, it was trimmed so well that it glided right down and made a perfect landing on its own. The pilot would have survived the dead stick landing just fine. It was not that particular rookie's day.
 
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