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Just completed a 12 volt conversion and new wiring harness from Classic Parts ( $150 ). In addition, added turn signal. Head lamps, dome, front parking lamps work along with front turn signal and emergency flasher- only the front. Fuses are ok. Prior to adding the turn signal the rear lights worked and at one point while testing, the rear lamps came on but not any longer. The connections look good. Any ideas? 53 1/2 ton with 235 engine.
Thanks, Scott

Hy scottss60, do you have one or two brake lights? Are your new turn signals using the two brake light filaments, (if you do have two brake lights) or are the turn signals using their own bulbs at the rear of the truck?

The turn signals are using the existing brake lights. I have two brake lights..which are new as are the front parking and headlamps.. I am wondering do I need to have a ground at the tail lights? The turn signal is just a switch and uses the existing lights... just checked again as it is dark.. no brake lights when pressing on brakes- no rear lights.. but they were working before I put the turn signal on.. all connections seem correct as I said, dome, head and front parking lamps, front turn signal and emergency flasher work..??

Perhaps my bulbs are bad.. but they were brand new.. I will check that tomorrow..

How many wires is your turn signal?

the tail lidgt have to have a good ground. some times there are to much paint between the housing and mounting bracket

Five wires. If the lights need to be grond, wonder why they were working prior to adding the turn signal...

Look at your schematic that came with the harness. Study it to understand how hot gets to the rear. Then see that it is wired correctly. Start at tail lights and see if you find hot with a ice pick tester. Be sure you touch the tester wire TO A GOOD GROUND. Grind a new place on frame for a good ground so the test will show whether there is hot at lights. That is the first step. Then work towards front to find hot. Don't assume some screw or bolt is ground. You can also run a length of wire from battery ground back to the rear temporarily. Take out bulbs, turn on lights and touch tester probe to each of the socket contact pads while this temp ground is attached to tester lead.
I have it in my mind that turn signal harness has 7 leads???

Will check tomorrow.

I was just installing the directional switch on the column of the 48. The switch is a repro with correct cloth wires (and 4 way).
There are 5 output wires, LF,RF, LR, RR, BRAKE RETURN, and one input wire from the flasher.
If you unplug the 2 rear connections, does the flasher work (but faster) and the front lights blink?
When you plug in the rears does the flasher speed change? If not, the switch isn't seeing the rear bulbs.
If it slows down then it is seeing the load, but a bad ground is back feeding through the the other bulbs in the rear.

The more light bulbs on the circuit the faster the flasher blinks, so one light bulb makes it blink slower (takes longer to heat the bi-metal strip with the low current flow).

Mike B

...

Scotts,
I just recently upgraded my turns to have two light fixtures Instead of 4 in the rear.
this meaning my brake/turn/parking light are in one housing. To achieve this I needed a 7 wire signal switch! This is possibly where you made a wrong turn! Pun intended! Standard bulb or LED? Doesn't matter to the end result but curious.

Mike B, you would think that would be the way, but in your street car you can always tell when you have a bulb out because it blinks twice as fast. Then again adding a trailer can sometimes make it blink faster.

When the trucks were built (47-53 anyway)There were only 2 wires going to the rear light(s). One for tail and one for brake, fixtures were grounded. Small bulb for tail and large bulb for brake, both single fillament.
When after market directionals were added, additional wires were run to the 4 light assemblies that were installed .
If you removed the add on directional lights and didn't change the rear wiring harness the brake lights are still connected together.

Jim, when you state "unplug the 2 rear connections " I assume that you mean the connections at the flasher? I notice that the front flashers work but seems pretty slow. What is confusing me is that prior to installing the flasher the brake/parking lights worked and I didn't have a specfic ground to them. Clearly I had current to the rear lights prior to installing the flasher.
Thanks for input, I will unplug the rears and see what happens.

They usually relied on socket to housing to brackets to body to frame for ground. All "touching/fastened" to each other. You can see the multipath problem of getting back to the neg battery terminal. That's why it's usually the ground. But I always start with making sure I have power first to the bulb contacts. Run, stop and blink power. The ice pick tester bulb will operate just like the real bulb...run, stop and blink. (if you have an absolutely sure test ground)If the power does not work with a good test ground, you work on the power distribution until you find it. If the test bulb works you redo/fix/add the ground path until it works. Again I say check the schematic from harness and schematic from Turn signal kit to understand the wiring. If you want to keep guessing theories you are wasting time. You need to buy a ice pick tester, take off the lenses, pull out the bulbs and test the socket in various modes.

Excellent advice, Bartamos

I try to read carefully but sometimes it does not click in. Please state how many actual rear lights you now have and how many bulbs. I am just making sure I am giving the correct advice for the system you have.

Here is the general wiring: You need SIX wires in the turn signal switch minimum. One input from the flasher, one input from the brake switch, one each output to RF, LF, RR and LR. You will need 3 wires back to rear. One from the headlight switch goes back and jumps from the drivers side tail light to the passenger. This is the smaller filament on a dual filament bulb. (1157) and are , of course, your tail lights. Then the LR wire and RR wire from the turn signal switch. These go to the bright filament contact on a dual filament socket. Each wire is BOTH the turn and stop input to bulb. Keep in mind that the brake switch input and the flasher input must go thru the signal switch so that the large filament can be "controlled" so as not to apply brake switch power at same time as turn signal power is applied. This would cancel out the flash. Hopefully you have only one light on either side of the rear with a dual filament socket in each.

EDIT:
I see Cletis and DADS50 were trying to help you in another post. This deal is really not to hard, but it is difficult sometimes to understand electrical. We will all take a deep breath and help you. It very much needs a fresh look at the whole system. There are not that many wires. Do you have a schematic diagram? This would help allot. Maybe a fresh retrace of the wires would help. Let us know. No problem. If you have difficulty reading the schematic, we will help. If you have difficulty testing a circuit, we will help. Just let us know if you need the basics. Maybe we are confusing you or using too many terms unknown to you. That's our fault not yours. Health care workers, Veterans, Active Military and First responders are TOP PRIORITY.
It's like me asking you how to deal with a patient, I wouldn't be able to do it even with your help.

The turn signal switch has color coded wires. The schematic/wiring diagram/instructions use these colors to tell you where they go. If you only have 5 wires coming out of the switch, I am confused and can not find a single diagram with only 5 wires. Please double check that and I will help connect them properly. We can go over the front and the back wiring. Will check back at half time.

[url=http://<a href="http://s651.photobucket.com/user/Scott_Schmidt/media/20151206_133834_zps2f2kkf9s.jpg.html" target="_blank"><img src="http://i651.photobucket.com/albums/uu231/Scott_Schmidt/20151206_133834_zps2f2kkf9s.jpg" border="0" alt=" photo 20151206_133834_zps2f2kkf9s.jpg"/></a>][/url]
this is the schemtic from the turn signal kit. as I said, the tail brake and park lights worked prior to me connecting the turnsignal. the front lights/turn signal/park lights work- though the turn signal flashing lights seem slow. thanks for all the input.

<a href="http://s651.photobucket.com/user/Scott_Schmidt/media/20151206_133834_zps2f2kkf9s.jpg.html" target="_blank"><img src="http://i651.photobucket.com/albums/uu231/Scott_Schmidt/20151206_133834_zps2f2kkf9s.jpg" border="0" alt=" photo 20151206_133834_zps2f2kkf9s.jpg"/></a>

That's what I expected. If you want hazard/emergency flasher it's 7 wires, if not it's 6. If flasher only has two terminals then BLK and BLU are both put on same and hot to the other. Check to see that you have the Turn Signal switch wired correctly. Exactly as shown.
How many tail lights do you have and how many tail light bulbs?

http://s651.photobucket.com/user/Scott_Schmidt/media/20151220_210113_zpstcvlwhrv.jpg.html
Hopefully this is my schematic.

Thanks everyone for your time on this issue. Prior to connecting the turn signal the rear lights worked. Once I connected the turnsignal per the diagram the front lights and turn signal work but nothing works in the rear. I have not tested for current in the rear but plan on it. The fuse is good. I have rechecked my wiring connections and they are according to the above diagram.

Yes, that's good. So a hot wire from the fuse box goes to the stop light switch..out the other side of that switch to RED T/S wire.
A wire from fuse box to the dimmer switch hot terminal...out the other terminal(s) to T/S BLK/BLU. Wire per schematic/colors to the front small park/turn sig lights and to rear lights. Does this all seem agreeable?
How many tail lights do you have and how many tail light bulbs do you have? Do you have one tail light on the LR and one on the RR with one dual element 1157 bulb in each and that's all the rear lights there are?
Trying to determine what work you did to the rear and what you added or modified because it does sound like you did something wrong. Mis wired something, disturbed something. Sometimes when we double check things we assume they are correct before we start. As a former paid Aerospace design checker, I advise you to approach it thinking it is wrong. Because something IS! This eventually will lead you to be a paranoid schizophrenic pessimist like me, but a good one! A trained professional S.O.B. OORah!
It is very hard sometimes to check yourself. Why did you say the turn signal switch only had 5 wires? Is there a clue there?

Just a heads up, from my point of view, some of Classic Parts harnesses and wiring aren't compatible. I went through a lot of time with my 63 Chevy. Put the old harnesses back in and they worked fine. The tech guys there alway gave me some song and dance about a proper ground, or that I bought the wrong part, etc. but whenever I put the old harness back in it worked fine. Just my opinion based on my experience. Don't waste a ton of time scraping paint and trying to figure out grounds. If the old one worked the new one should in my opinion. Some of the harnesses worked and others didn't seem to.

I can see on a newer truck as wiring got more complicated and had some flex print and ignition changes, etc., and electric went to electronic, analog to digital, that harnesses would have to be more "custom fit" possibly...but on an old truck, it cant be simpler. Albeit grounding is a real problem with them and is the cause of trouble more than %50 of the time.
Using the body, frame, motor, sockets, brackets, bolts, screws and intimate contact for ground creates dozens of places to corrode, get loose, get isolated, rust out, break and cause intermittency and failure. Over and over again. I've never blamed a new harness for anything. It's just a bunch of wires, most of which come out of a fuse box. The correct hook-up is up to the user.

http://s651.photobucket.com/user/Scott_Schmidt/media/20151208_113325_zpsyys1319p.jpg.html
here is a photo of the two sets of wires. the one I am holding is from the new turn signal and the other from the new wiring harness which is numbered 31 - 35 and correspond to the colored wires off the turn signal( #31 corresponds to the LR for example ). I just connected them as such. I am confused re ground. Prior to the turnsignal the rear lights worked and I hadn't grounded them. BTW, there are two rear lights each with two filements. Anyway, thanks for all input. Weather permitting I will test current to rear lights and work my my back?

Scottss60,

Are you able to disconnect the wires going to the rear lights where they connect to the turn signal wires. If so disconnect the wires going to the rear lights. Now take a jumper from the positive side of the battery (or any hot 12v locations) and connect to one wire going back to the rear lights. Check and see if one of the bulbs lights and take note of which part (ie taillight or brake light). Do this check for each rear light. From your description there would be three wires to check in this manner. If the bulb does not light then there is only a couple of problems to check - no ground, broke/disconnected wire probably where connects to rear light and wiring harness, bad bulb. If the lights all work after this check then the problem has to be associated with the turn signal unit. Remember with electrical parts it is always best to try and check each section out and verify that it works then add the next section til it quits working.

Hope this helps,
Chuck

Update..well I finally realized that I should check the rear light bulbs and found out they were 6volt not 12..replaced with 12 and lights work though not with the turnsignal..ran to auto parts store for 12 volt bulbs ..shouldn't they be two filements to donate tail and brake? I put in single without realizing it.. a bit cold outside for now.. thanks for all the suggestions..now why won't the rear lights work with the turnsignal??..

If you only have one light/bulb on left rear and only one light/bulb on right rear....YES you need an 1157 bulb. Good work on getting the lights to work some. I assume you are talking about turning them on with the headlight switch???
It is fine that you hooked up the main harness to the T/S harness. However you need to follow each wire with your eyes to see that it goes where you think it goes. Also, do you have three wires going back to rear? However many you have be sure you can see where they go, write it down and compare to schematics. You are half way done. Did the 6V bulbs blow out? Do you have 12V bulbs everywhere now...front, dome, dash lights, headlights...???
EDIT: you need TWO contacts down inside your rear bulb sockets NOT one.
IF YOU HAVE ONLY ONE...this is your problem and is the answer to why no turn sig lights. Please advise.
Are you sure of this comment?
"BTW, there are two rear lights each with two filements."
You said this in the post before you: discovered 6V and replaced with single filament and ask about two filament. Please take out bulbs and look inside sockets and see how many contacts you see. One in the middle or a pair.
As far as ground, you have ground if the bulbs light.
A single will NOT fit into a double and vice-versa because of the lock pins being different.
Both equal and low= Single (1156), off set=dual (1157)
(12V bulb part no.'s)

http://www.oreillyauto.com/site/c/d..._1489146_2546&pt=N1587&ppt=C0243