1978 Diamond Reo electrical

[cxn613]

trying to get some help, put a flatbed on an old Diamond Reo truck. Wired everything up using what was there and everything works but the turn signals when the brake lights are lit. When I power probe the stud for the right tail/brake the left lights up to. Same when i probe the left, the right lights up as well, but when i unhook the wires from the truck to those studs they work as they should when putting power to the stud for left/right turn/brake.  So seems to me there is something from the truck pig tail back to the cab making both energize when power is put to one. What doesn't make sense is the signals work when turned on with the turn signal unit.

[tjc transport]

most of the older trucks used separate turn signal and brake lights. that is why you see three lights on each side of older trucks. reverse, turn, and brake lights on each side. 

[Vladislav]

There might be a ground wire issue.

Current can't go to the ground and finds its way through another light bulb.

[fxfymn]

As Vlad said that is most likely a bad ground. Try connecting a ground lead from the light directly to the battery and see what happens. (I use a trailer wiring harness as a set of test leads; they are long enough to go from front to rear on most vehicles and color coded so you can test multiple circuits.)

[cxn613]

Thanks for replies. With further head scratching i believe whats going on is i have one wire coming from brake switch, so when i bug into that one wire to run to the left turn/brake stud and the right turn/brake stud, when you turn the signal on for either direction its lighting up both sides because its feeding through the one wire i split for the two studs. The flatbed has 3 center clearance lights in back and then two big clearance/turn/brake on each side in back. I thought about just making the outsides just clearance and turn and then the ones right beside them be clearance and brake, but it has 7 pin r/v trailer plug that would have to be wired accordingly. Or do i just need two brake switches at fire wall to run to left and right that way theres no crossing like i stated above. 

[Brocky]

Most Older trucks were set up for separate brake and turn lights in the rear. So if you have a newer turn signal switch, possibly that is where your turn signals are getting crossed with the brake lights.

Your thinking on separating the brake and turn lights in the rear is correct and might solve your problem. The 7 pin plug should have bottom center (6 o'clock) as a red brake wire and 4 & 8 o'clock be the green and yellow turn signal wires. 

[66dc75]

The wire from the load side of the brake light switch goes through the turn signal switch and you will  have  left and right turn signal leads coming from the switch to go to the rear of the truck.  These will also take care of the brake lights. There are 2 other leads from the switch that run the front turn signals which are isolated from the rears so the fronts don't come on with the brakes. Most of the time green is right yellow left and brown running lights.  If you have left and right leads already hooked up disconnect the wire bugged off the brake switch and see if everthing goes normal 

[gearhead204]

your brake light wire need to run thru the turn signal sw. (you may need a newer style sw. to do this) if you want to run a 2 light system. (brake turn tail all in one light) if you go with a 4 light system the out side lights would  be turn/clearance the inside would be brake or brake and tail. if you are running a 7 wire pig tail the latter is easer, it can be done with a 2 light system but you need a junction box ahead of the turn signal sw. in order for things to work right in the  wire.   If the 7 wire would always be pulling a 2 light style trailer you could junction off the rear of the truck and have a spare circuit.   

[cxn613]

I have a 900 series turn signal switch which looking at a diagram i see were it says the one wire should go to brake switch. The  wires were disconnected at brake switch and in bad shape, so i ran a new wire from brake switch back to harness going to rear of truck, question is can i just bug into that wire that gets hot when brake is pressed and run it to the wire it needs to go to on turn signal switch?

[85snowdog]

Like the guys said above, signals and brake lights go through the turn signal.  If you have a separate brake and signal going to the back.  I think you could  wire in a

 4 to 5 wire converter. They are used for  vehicles that have separate brake and signal lights that need to be converted to a single light that operates both brake and turn. They're not very expensive , and you should be able to get it at any trailer place.

 

[tjc transport]

yes. that would be the way to do a 2 light system. with the way it currently is set up you need to run the 4 rear light system the truck came with. 

[Hobert62]

1 hour ago, 85snowdog said:

Like the guys said above, signals and brake lights go through the turn signal.  If you have a separate brake and signal going to the back.  I think you could  wire in a

 4 to 5 wire converter. They are used for  vehicles that have separate brake and signal lights that need to be converted to a single light that operates both brake and turn. They're not very expensive , and you should be able to get it at any trailer place.

 

I got mine at "advance auto" for $25 if I remember right

[cxn613]

Got lights and plug working on truck, thanks for the help. Next question is the truck has two headlights per side, the owner had taken one round light out per side and mounted snow plow lights. Now they want it returned back to original, question is do all four come on with high beam or do they use a one high and one low beam per side?

 

[41chevy]

3 minutes ago, cxn613 said:

Got lights and plug working on truck, thanks for the help. Next question is the truck has two headlights per side, the owner had taken one round light out per side and mounted snow plow lights. Now they want it returned back to original, question is do all four come on with high beam or do they use a one high and one low beam per side?

 

Outer two for normal and all four on with Hi Beams.