Reverse Light Issue - help with my theory (1 Viewer)

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

Joined
Nov 25, 2008
Threads
38
Messages
158
Location
Austin, Texas
78 FJ40 w/H55

My reverse lights aren't working. Everything else back there is. Checked the bulbs and ground. Good. I was going to start with the reverse switch, but had the rear light covers off today to freshen up with a light bezel refinish kit from Cerakote (amazing btw), so started back there.

Here's what I found:
1) I do not have continuity between both sides of the reverse lights.
2) I put the vehicle in reverse, no power to either side

I don't have a wiring diagram, but assume at some point the positive wires for the reverse lights meet up somewhere in the wiring harness before the reverse switch - does anyone know where?

In the mean time, I'm going to confirm I have 12V coming off the reverse switch when engaged. But the fact the two reverse lights don't have continuity to each other is concerning.

Thanks!
 
The reverse light wiring runs off of the passenger (RHS) side firewall down past and over the nose cone of the transfer case and up to the switch. If OE, there will be a clip holding the harness and two bullet connectors (late split cases had an updated connector). Hopefully it's just unplugged
 
The reverse light is powered through the heater fuse on my 77, and the blue-red feed wire runs down the main tail light harness along the right hand chassis rail. It hops over the tunnel to the reverse light switch and then back again to the harness as a white-blue switched feed.
This runs to the rh tail light, and splits off at a solder joint just before it get there, to the left tail light - joint is hidden in a lump in the harness where all tail lights are split off.
So yes they should be connected together.
Crawl underneath and check your tail light wiring :)
 
There should also be a factory junction in the harness as it comes down the right frame rail, about where the crosstube is for the rear shocks. It's before the whole rear harness does its splitting to the left/right, so it's a good spot to troubleshoot.

Reverse should be a red/blue or blue/red...but it's a small set, I think it's only 5 wires (left/right turn, brake, tail, reverse). If you're getting 12v there, the problem is isolated to the rear harness. If not, it's up front.

Screen Shot 2023-04-08 at 4.32.56 PM.png
 
Isn't the switch in the tranny switching ground?
 
I believe it's switched positive in this circuit, although Toyota did run some circuits switched ground.

It's definitely positive running down main harness along the frame rail into the rear harness. Diagram show +12 from the fusebox running to the trans switch as well.

Screen Shot 2023-04-08 at 7.00.54 PM.png
 
I found this in another thread - I'm going to finish diagnosing tomorrow. This is a great diagram!!!
 

Attachments

  • fj40_wiring_diagram.pdf
    445 KB · Views: 31
On a four speed the reverse switch is on the back of the top cover. H55F it will be on front no matter a 40 series or a 60/70 series top cover. Plug on the reverse light switch are different between four speed and five speed. Would start there. Reverse lights are grounded at the tail light. I would check the wiring at the transmission. With the wiring unplugged by the switch and jumper across the two wires in the harness the reverse ignition key on should power at the harness to the back.
IMG_20200219_134927139.jpg
P1050661.JPG
 
Well, the easy part. I have a small access panel on my transmission inspection panel that was put in when converted to a H55 - so whole inspection panel didn't have to come off! And I found the reverse switch unhooked. And the switch tested good for continuity when put in reverse.

The bad part. None of the wiring colors for the rear backup lights match wiring diagrams and they are original connectors. That's OK. I found the 2 solid blue wires from each reverse light have have traced them to point near the transmission where two cut ends are exposed (don't know if this is both wires or the wiring is cut here and joins somewhere else - going to test that in a minute). there are also 2 BR (or RB) wires that are cut. So I am close since the reverse input in BR and output RB on the diagram. And there is a black wire there as well? And I found a bullet connector unplugged further up that was RB/BR (very dirty). So, just checked continuity of this mess and find the right wires. Worse case, I tap 12V somewhere and just run all new wires from the 2 solid blue wires. When I retire (in 3 years) - doing a frame off and a new wiring harness.

Screenshot_20230409_092435_Gallery.jpg
 
Btw - what is this on the side of the transmission? Temp gauge or something else not used on a FJ40?
Screenshot_20230409_092423_Gallery.jpg
 
Last edited:
OK - Per above, I had 4 wires located. The plain Blue wires each went to the reverse lights. But the two BR cut wires and the unplugged BR wire with the bullet connector are ALL 12V hot w/ignition turned on. So don't know where they are picking up power. Doesn't matter, I have a hot lead at the bullet connector that is right next to the reverse switch. I'm going to order the proper connector, connect the hot wire and then run the other back the 2 blue wires. And the two hot wires, I will separate and cap (like I found them). And then in 3 years, I will give it a proper frame off. But when i wired them together and turned on the key, I had reverse lights!
 
Last edited:
BTW - does anyone know where to find the correct matching plug for the reverse switch? I can always wire in a generic one.
 
Coolerman sells proper wire, terminals and plugs. The wire going to the reverse switch is suppose to be hot with the key on.
 
Thanks! So not needed :)


If you dash has an unfilled hole that fits the round turn signal/brake light/4WD used on re earlier models can hook up a light to show when you in 4WD. Can tap into the 12 volt positive wire going to the reverse light switch. Hook that up to one wire on the switch on the transfer case. Then connect the other wire a wire going to the plug the dash fit in and your done.
 

Users who are viewing this thread

Back
Top Bottom