Rising Sun Member Forums

Rising Sun Member Forums (http://www.risingsun4x4club.org/forum2/index.php)
-   General Tech Forum (http://www.risingsun4x4club.org/forum2/forumdisplay.php?f=17)
-   -   FJ40 Brake Lights (http://www.risingsun4x4club.org/forum2/showthread.php?t=8166)

RicardoJM 09-11-2008 12:06 PM

FJ40 Brake Lights
My rear Brake lights do not work and I'd like to get it sorted out. The fundamentals of an electric circuit are pretty straight forward in concept and in practice the FJ40 wiring is about as simple as it gets. As with most things, this is new to me, but I'm ready to learn:D. I've got the Chilton manual with wiring diagrams and have found some wiring diagrams on the internet as guides. None of these sources match up exactly with the wiring that is currently in my truck, but there is enough information for me to formulate and understanding the circuit components that are involved. As I start this, there are a couple of basic understandings I'm hoping the board can help me with.

I would appreciate some confirmation/correction regarding my logical understanding of the circuit. The power for the brake light circuit starts on the Fuse Box (FB) and travels to the Stop Light Switch (SLW). From the Stop Light Switch it goes to Turn Signal Switch (TSS). From the Turn Signal Switch it flows to the Combination Lights (CL) at the rear of the truck. The Combination Lights are grounded to the frame to complete the circuit. There is also wiring From the Turn Signal Switch to the Hazard Warning Signal Switch (HWSS) and back. Basically:

For those of you that have experience with the early FJ40s - is this basically correct?

I'd also appreciate some confirmation/correction regarding my understanding about the rear Combination Light portion of the circuit. The Combination Light has two wires that enter the housing; one wire carries juice for a single circuit (Tail), the second wire carries juice for three circuits (Hazard, Signal and Brake)and all circuits make a ground connection to the frame of the FJ40 via the bolt(s) that mount the rear Combination Light housing to the frame. Presuming this is correct and coupled with my Tail and Signal lights work. Is it safe to assume the ground connection of the rear combination lights is ok?

MDH33 09-11-2008 12:45 PM

Your understanding of the wiring seems right on. The ground could still be the culprit. My signals didn't work, but the running lights and brake lights worked, and that was a poor ground. Could also be a fuse, as I think the brake lights are separate, correct? Clean up the grounds and the blades on the fuse panel first, then start tracing the wiring. Have you checked the brake light wiring in the back with a test gauge to see if it's getting any power?

subzali 09-11-2008 04:25 PM

And make sure it's not the bulbs. Seriously.

What I did was take a wire from the battery and I found the connector in the engine compartment that separates the wiring harness for the front part of the truck from the wiring harness for the rear part of the truck. Disconnect it and touch the wire to the contacts and see if the lights work. If they don't then you know your problem and can forget about stuff further upstream.

RicardoJM 09-11-2008 08:56 PM


Originally Posted by MDH33 (Post 85821)
The ground could still be the culprit.

Give that man a FJ60 differential:bowdown:.

I started off by removing each fuse from the block, cleaning it up with some steel wool and running a round file through the fuse box clamp. I figured it was the easiest step in the debugging process and I could only be better off for the cleaning. I also checked each fuse for continuity to make sure they were good. After this step, I checked my lights, they seemed brighter but still no brake light.

Next step was to clean up the ground connection between the combination light housing and the frame. I started on the drivers side and in short order busted the head off a bolt:


I hate it when that happens, now I have to get the rest of it out. Hopefully it goes smooth and I don't have to drill it out and re-tap. At least I've had this experience before and know what to do. :thumb:

Thankfully there are two combination lights on the rear, so I moved over to the passengers side and took out the two bolts holding the combination light housing to the frame. Both the frame and back of the housing were oxidized that burnt orange color that is familiar to FJ40s. I sanded on both until I could see shiny metal like this:

and this:

I bolted the housing back up to the frame and checked the lights. :woot::woot: The brake lights work.

MDH33 09-11-2008 09:08 PM

Awesome! I have a broken bolt on one of mine too. :o

I PB blaster everything now. I love that stuff. :thumb:

Rzeppa 09-12-2008 12:54 AM

Late to the thread, I see you figured it out. On my 71, I put a separate wire with lugs to go between the one of the two bolts that mounts the bracket to the cross member and one of the three studs on the back of the combination light assembly. It has worked flawlessly since I installed it, and even works when you smash the combination light on a rock :-)

In respect to with Matt's suggestion, I once had a seemingly incurable problem just before CM2004. No lights, no blinkers, no brake lights, nada zilch. Lots of troubleshooting with DMM and visual and such failed to find cause. Finally checked bulbs. All 4 filaments were history, new bulbs solved the problem. Figured out root cause: Installing new lift involved lots of pounding with BFH on shackles and such, too many Gs for the filaments :-)

Rzeppa 09-12-2008 12:56 AM

Oh, speaking of smashed 71 tail lights: Brand new combination light assembly is $22 and brand new bracket is $12 from Stevinson. Righton!

kvanoort 09-13-2008 08:31 PM

I had the same problem with my '72 40. I started with the cleaning the fuses and replacing the bulbs with new and then cleaned all the wire connections close to the tail lights and voila the lights worked. What I found out is that it is usually a ground issue. My front turn signals required wiring up a separate ground wire to each assembly.

RicardoJM 09-17-2008 12:22 PM

After getting the lights working, I found that the intermittently they worked too good as the brake lights would remain on after I took my foot off the brake pedal:confused:. Turns out this issue was caused by the brake light switch not opening to break the circuit because the brake pedal did not consistently "pull up" to open the brake light switch.

Some research on the net and I learned there is a spring between the steering column and the brake pedal that provides additional "pull up" when my foot is taken off the brake pedal. I had been wondering what the spring hanging unattached on my steering column was for and now I know:D. My spring was not attached to the brake pedal, after hooking it up, my brake pedal goes all the way up and the brake switch opens - which results in the brake lights turning off. :thumb:

Observation, I always get a giggle when I am researching issues on MUD and I come accross RS Club Members that experienced the same issue and/or provided input/guidance to someone else on the issue. There is a wealth of experience and knowledge in the club.

Rezarf 09-17-2008 01:03 PM

Ricardo- Another place to clean up is the bulb socket itself. A bottle brush style wire brush (like the ones on the end of a battery terminal cleaner) is great, I add a touch of di-electric grease to all my connections... a little marine tip, from growing up on the coast and that seems to go a long way in keeping them clean and corrosion free.

Good on you for diving in!


All times are GMT -6. The time now is 02:31 AM.

Powered by vBulletin® Version 3.7.1
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.