Trailer wiring help

[bmacster]

I am having a hell of a time trying to hook up the brake light wire for a 4-flat trailer converter/harness setup. Truck is an 85' 720

 

The confusing part I am having with the setup is when I press the brake, the lights on the LED indicator show that it is 'connected' to the proper source, however, when hooked up to a trailer (went down to u-haul, just in case) and tested the lights out there, no brake lights.

 

The red brake light wire on the harness is not connected to anything however. Any ideas or know which wire it is supposed to connect to? It "looks" like it should connect to the Red/Yellow or Green Red? Both of these wires seem to lead to the bulb socket. The 81 wiring diagram is not helping.

 

Thanks!

[datsunaholic]

There is no brake light wire for a 4-flat connector. The brake lights are combined with the turn signals, as is a '85 720 ('85-86, 84 and before have separate turn/brakes) There are Green, Yellow, Brown, White on the trailer connector.

 

Green is right Turn Signal (which is also right brake)

Yellow is left turn signal, (which is also yellow brake)

Brown is Taillight (running lights)

White is ground.

 

I don't have a '85 (or 86) wiring diagram so I can't help, but you need whichever wires are right tuns signal, left turn signal, tail, and a ground. I always use a fresh ground to the frame, and generally use the license plate light wire for the taillight.

 

On a trailer connector, RED is only used on 6 or 7 way, and it's Battery (HOT), for providing power generally to travel trailer accessories or charge the trailer brake emergency battery.

[bmacster]

I am not sure if this picture will help, let me know and I'll take a different one.

 

 

Part of me is wondering if I should tap into the wire and test out the brake light. It might be that the converter won't work right unless that red wire is connected to a source. I have everything else soldiered to the harness just out of the picture.

[Laecaon]

Ok you have a box, that is to convert trucks that have separate brake wires to combine it with the turn signals.

 

According to Datsunaholic, you dont need the box at all, and can just use the plug at the end (cut the box off and just wire the plug on).

 

Since you have a 85, you essentially have 4 wires to each tail light:

ground

reverse

running/tail lights

and either right or left turn/stop

 

 

Also, the converter does indeed need 12V+ power.

 

 

You tail light looks like this right?

[wayno]

Ok you have a box, that is to convert trucks that have separate brake wires to combine it with the turn signals.

 

According to Datsunaholic, you dont need the box at all, and can just use the plug at the end (cut the box off and just wire the plug on).

 

Since you have a 85, you essentially have 4 wires to each tail light:

ground

reverse

running/tail lights

and either right or left turn/stop

 

 

Also, the converter does indeed need 12V+ power.

 

 

You tail light looks like this right?

 

 

This man is correct, on a 85 720, you do not need the converter box, that is only needed on 80 threw 84ish 720s where the turn signals and brake lights are separate.

[datsunaholic]

Mentioning that you had a converter box would have helped. It's totally not necessary, in fact cannot be properly installed since you don't have a separate brake light to connect to. For a 520 or a 80-84 720 it's needed, but for 620s and '85-86 720s it's not.

[bmacster]

Ah, gotcha. That would explain why the prior owner had just the connector and no box. See what happens when you just go on what the people at U-Haul say? Le Sigh.

 

I'll cut it all off and try again tomorrow. Thanks a lot!

[bmacster]

All fixed! Thanks guys!

 

Now to find a hitch... Are there any out there that aren't a weld on type thing? Or better question, are there any hitches that will even fit the truck? Towed a small 7x10 trailer today... That was an interesting experience... No power at all going up any sort of hill.. or bumps.

[kakanu]

http://Users/JenJon/Desktop/Image 3-12-21 at 10.24 PM (2).jpg  

 

Help I recently did a bed swap from 84 to 85, prior to that everthing works on my truck.  Now my issue is I have no brake light but everthing else works, after going thru with test light I have power in the harness to rear coner of chassic where connector plug. After looking at the connector the 85 only has 5 prongs the 84 has 6 prongs. Can someone point out how to fix issue

[Charlie69]

The 85 taillights have the reverse light included in the assembly.  The 84 has the reverse light in the roll pan.

 

I would take the wiring lights and roll pan from the 84 bed and install on the 85 bed.

[kakanu]

Will try that and get back to you

[Charlie69]

This includes the 84 harnes that plugs in under the passenger seat and runs back along the passenger side frame rail to the fuel pump, gas tank and then continues to the rear end of the frame rail she the taillights harness plugs end.  The taill light harness has a ground eyelet on it, and will connect to the taillight pigtails, the reverse lights, an the license plat lights.