The Stovebolt Site Forums The Shop Area The Electrical Bay '59 Apache - rear turn signals very dim when tail lights are on

All lights work fine EXCEPT rear turn signals when tail lights are on. With tail lights off and/or brake light on or off, rear turn signals work great. Only when the tail lights are on do the rear turn signals become so dim as to be unnoticeable. You can only see the turn signals flashing with red lense removed and your eyes 2 inches from the bulb. Front turn signals work fine in all positions. All lights work great except for the rear turn signals in this one position. I have replaced the following: 2 new rear 1157 bulbs, 2 new rear pigtail wiring harness with bulb sockets, new headlamp switch, new 2 prong flasher. Truck does not have hazards. I had this problem before I replaced these parts. I don't know where the ground is for the rear lights so I haven't inspected that. I don't see any wiring issues underneath the truck (I had it on a hoist). Any help would be greatly appreciated.
Chim Chim

Ground probably. To test: remove lens, Turn on a blinker, touch a pointed metal tool with a wire in it to where bulb enters the socket. Touch both bulb case and socket at the same time. touch other end of wire to a GOOD CLEAN SHINNY ALL METAL place. When I say "touch" I mean dig in. Build this test rig from what ever you have and make sure the wire is attached well to the touch tool. Do this until it lights and blinks bright. If you get it to blink bright then break it down to what it needs I.E. separate ground wire from socket or bezel to a spot on frame. If you don't get bright blink: Another good test: take out the bulb you have trying to flash and, with one of those lighted testers with ice pick looking tip, attach the alligator clip to a good shinny ground and touch the tip end to a contact down inside empty socket, One of those is the blinker. It should flash the test light. If it does, proceed as above to buzz out the circuit including GROUND. The second test will tell you if you are getting good blinking voltage to the socket contact. Be sure the filament trying to flash is the bigger one, that one is for brake and turn, the smaller is for tail and park. When you say they work except when tail lights are on, it's either cross wired or the tail light together with flasher (both filaments at once) is "breaking down" a weak ground. Don't forget all this stuff goes thru the turn sig wiring and back out and thru various connectors. Check that stuff too. Report findings so we can all learn, that's what we expect here. You need to let us know. Maybe I'm on the wrong track but I need to know to continue till it's fixed. Others will have more ideas.

It sounds to me like the signal and tail filament connections are reversed. One filament in each bulb is brighter than the other and the brighter one should be connected to the signal/brake indicator.

The bulbs get their ground through the metal base they go into. So it has to have a good ground to the body.

I'm with Bart on this that you likely have a bad ground.

Yep, sounds like bad ground.
Same symptoms on my 58 Buick .... A bad ground can make symptoms "float" through the system mysteriously. The light housing itself must be
well grounded to body/chassis.

Sounds like what other here have said. Crossed wires or bad ground. Let us know what you found.

The wires are 'crossed' inside the bulb. The circuit can not get a ground through normal channels so it is running through the other filament to find one.

Thanks for your responses. I'll be getting back to the truck sometime this week and will let you know what I find.
Before I do, I have a couple questions based on your responses. How would the wires get crossed? The new pigtails I installed each had two wires, orange and black, that are attached to the new socket. The new wires looked like you could attach them to the old two wires either way. I attached the old black to the new black and old white to the new orange. Does it matter?
Secondly, each socket locks into a hard metal cup like housing that has two sheet metal screws that attach it the body. Is where the ground is? Or is it the outer ring of the "cup" that has a soft metal ring placed behind it that rests against the body?

you've answered your own question, wires get crossed when you make assumptions about different colors - you should check which filament the orange wire is for, should be the brighter ['old' white = brake/turn] one, the black should be the dimmest [tail] filament, and you should insure you didn't make any changes elsewhere in those circuits

for the ground, from your description it sounds like you have a fleetside, so, yes the screws that mount the light assembly to the bed provides the ground, but the bed needs a good ground to the frame, which can easily be missing, best practice is to add a wire from the rear cross sill directly to a bolt on the frame

Bill

Yes 2-wire systems do matter. You have two filaments in those bulbs - a large (bright one) for brake/turn and a small filament (dim) for tail light. If the large one is getting the (wrong) tail light power it will be so bright you can hardly see the turn signal emitted from the small filament.
So both wires are power, the circuit is completed via the metal parts back through the body to the battery. If the ground is weak (socket to fixture, fixture to body, body to battery) the one light might appear normal until the other light is activated and then the resistance is so great both filaments will be dim.
Mikey

After you do some tests as I explained, we will be closer to answering the crosswire and ground questions. Bottom line to always remember when doubting this and that is: Something is wrong! Something needs to be tested and found. Something needs fixed! No one knows what it is yet. A troubleshooter NEVER assumes anything is correct because something isn't. I have run a wire from my battery ground back to my tail lights and touch it hard against bezel, then socket, then bulb base to get them to light because you have to sometimes bypass every ground to get a baseline. If the bulb doesn't light then, you know it ain't a ground problem. Let us know what you find out and we can continue to help or maybe you will fix it. Thanks

Ok guys, I finally got back to this part of the truck. Thanks for your earlier responses and your patience. The problem was that the wires were crossed as many of you suggested. The new pigtail wires had one orange wire and one black. It turns out the correct connections are:
1. the new orange wire to go to the old black wire
2. the new black wire goes to the old white wire.
Now everything works as it should. I installed an extra ground strap from the fleetside bed to the frame just for the heck of. I did this before I reversed the wires to their correct position. It made no difference and I still had the same problem. Once I reversed the wires, bingo! But heck, since I ordered a nice ground strap, figured I might as well use it.
Thanks to all of you for your help. It is greatly appreciated. I've been doing tons of mechanical work on this truck and will post some photos in the near future.
James

Uhmmm.. after just rereading the earlier responses, it seems that possibly the body alone is the ground to the battery and the frame has nothing to do with it. In that case, I'm guessing my installation of a ground strap from the bed to the frame is completely useless, unless I consider it a nice reminder of how I sometimes get things a little bit wrong but learn something from it in the end.
James

James, the battery ground from the factory bolts to the firewall right behind the battery, lower down under the toeboard [red X] there's a ground to the engine, it's good to have externally toothed star washers under those connections - the frame should be grounded via the cab and engine mounts - the 'body' [bed] didn't have a dedicated ground originally, but it's a good idea to add one from it to the frame

Bill