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Rear stop light & turnsignal wiring
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By twin inset - Saturday, October 01, 2011 5:06 PM
In case you didn't understand Swishy, by bad earth he means bad ground. If you have a bad ground
the current will "jump" to another circuit that has less resistance and make lights light up that have
nothing to do with the circuit you want to be lit. Often times a clearance light circuit will blink when the
turn signal or brake lights are actuated. That is because the clearance lights are using the brake/turn
circuit as a ground and when current is applied to to the brake/turn the clearance lights go dim or
out because they now have no or little ground. It can be one of the most frustrating things to fix.
First thing to do is make sure your circuit has a ground. Then check all grounds for being clean and
making good contact. When electrical systems are not used they tend to deteriorate where ever
there is a connection. Dialectic grease helps to keep the elements out. Get a good test light. Make
sure you don't have a wire that has broken inside the insulation. Whiskey helps but stay away from small
arms. These things can drive you nutso! Report back when you find it.

By - Saturday, October 01, 2011 3:01 PM
I'm getting my 1972 White 4000 on the road for the first time in its life. This truck was never titled or registered & spent its life up until 15 years ago (when its batteries died & nobody wanted to drive her anymore) pulling an end dump at a TXI concrete plant in Texas. With an oil change & 3 new 12v. batteries the NHC 250 fired up and ran great. Every thing is going well with this project because the truck was maintained rather well & wasn't abused to badly in its work life. It just got to old for people. The concrete dust however has eaten some holes in the cab & removed almost all of its paint.
My problem at the moment is this: Since the truck was never out of the pit and always had the same trailer latched to it ,it did not have tail lights on the tractor. The wire harness, connectors & 2 brake light switches are mounted in the usual White place on the floor between the driver door & seat. They are in great shape and still have the number labels. I've mounted the lights & run a 4 wire factory harness from a parts Frieghtliner. The turn signals and markers work good & bright but when the brakes are applied they override the turn signals. Turn signals or 4-ways well not override the brake lights & blink. Front turn signals well not blink with brakes applied either. I'ts either stop or blink but not both if I'm making sense.
I'M HAVING A MAJOR BRAIN FART and can use your help. What did I do or not do? Did I forget something? I know its hard to diagnose electrical problems with your eyes closed 100's of miles away. Any help is mucho appreciated!
By - Saturday, October 01, 2011 7:35 PM

  I think you hit it. I have a Signal-Stat 902 Sigflare with 3 wires. That makes sense on the seperate brake light thing because there is a seperate wire on the connector strip number labeled for stop  lights. I guess that switch was fine for working the trailer lights since the truck didn't have or need tail lights. I was going crazy with this because I have 2 Pete's with the turn & stop on the same wire & could not figure out why it wouldn't work on this truck. It looked like everything was the same but after you asked about the switch I took  the bottom covers off of the switches in the Pete's & they are the 7 wire. VSM 900's. I'm guessing my two options are either wiring the tail lights like a trailer with 4 lights (which I did install a 4  round light tail filler panel) outboard lights would be marker/turn & inboard would be marker/stop? Or replace the turn signal switch with a 7 wire? What do you think? If the first option well be ok I think that would definitely be the easiest in this situation to do.

  Yes. The ground is good.

                                                                             Thanks, Tim
By Swishy - Saturday, October 01, 2011 3:09 PM
Bad Earth will do th@ |||||


By Geoff Weeks - Sunday, October 02, 2011 4:11 AM
Easyest is to run two more lights and one more wire (to feed both brake lights) but changeing the switch isn't hard either.
By Geoff Weeks - Saturday, October 01, 2011 4:31 PM
What turn signal switch do you have? There are two kinds, one is used if seperate brake lights are used and has no provision for "overideing" the brake lights for turn signal, the other (has 7 wires) feeds the brake lights thru the turn signal switch and will "overide" the brake  lights on the side the turn signal is selected.
By Brown Dirt Cowboy - Sunday, October 02, 2011 5:26 AM
Unknown, I had a question about turn signals a while back and Geoff helped me out with it. Listen to Geoff, he is pretty keen on this stuff. I went back and bumped my post to the top for you. The post was titled "I need an electrical guru". Hope this helps.