Fj40 brake light issues

[jlhollowx13]

Hi all, I have a 71 fj40 with fj60 disc brake conversion. Last year I was having issues with my brake lights not working, in the past they have worked fine. All other lights seem to work fine, tail lights, etc. I dug into it today and have been researching on here, but am almost more lost.

I have no wires going to my master cylinder. I took out the brake pedal switch, took it apart and inspected. All seemed OK. Put it back together and my brake warning light is now on, something that has never worked, even with the parking brake on (didn't know it was supposed to until today). It will turn off if I push the pedal hard enough. I'm thinking of getting a new pedal switch to start, but it seems I should have a wire for the master cylinder. Where should that wire come from? I've kind of had electric gremlins with the brakes/lights throughout the years but seemed to always end up being a rusted main ground, etc (which I cleaned today as well). I'm thinking now something isn't wired right, as I believe it was rewired at some point in its life.

I appreciate any insight. I despise electrical, but seem to always be dealing with it!

 

[jlhollowx13]

Also, I will mention you will see an unconnected blue wire at the top of the picture. It has 12v power, I believe it was for the old electric choke before i converted to manual, or for the temp guage that I (think) I unhooked when I put in an aftermarket temp guage because I believe I fried the OEM. It was many years ago so can't remember exactly what that one was for and both are within reach.

 

[Jonathan Hanson]

Not sure if this will help, but I had a maddening issue with intermittent brake lights—sometimes they'd work, sometimes not. I tried everything—grounds, replaced the hazard switch. The issue turned out to be in the turn signal assembly, believe it or not. It (in my '73, at least) also routes the brake lights. Replaced the assembly and the issue was cured.

 

[jlhollowx13]

Not sure if this will help, but I had a maddening issue with intermittent brake lights—sometimes they'd work, sometimes not. I tried everything—grounds, replaced the hazard switch. The issue turned out to be in the turn signal assembly, believe it or not. It (in my '73, at least) also routes the brake lights. Replaced the assembly and the issue was cured.

Thanks! Another thing to look into for me I think. My right turn signal only works if it's in a certain spot, I think it's wearing out. Might be worth me replacing that while I'm at it.

 

[pb4ugo]

The brake light switch you worked on activates the brake lights. The hazzard and turn signal switch are involved too. There's nothing on the master cylinder except pressure sensors, which activate the light on the dash along with the e brake lever.

I would have started my diagnosis at the rear lights and travel towards the frt looking for power with the pedal depressed.

 

[jlhollowx13]

The brake light switch you worked on activates the brake lights. The hazzard and turn signal switch are involved too. There's nothing on the master cylinder except pressure sensors, which activate the light on the dash along with the e brake lever.

I would have started my diagnosis at the rear lights and travel towards the frt looking for power with the pedal depressed.

I suppose I jumped to conclusions, as I admit to not checking for power at the rear with the pedal depressed. My assumption was if my blinkers are working, I'm getting power on the wires that power the brake lights, I assume the blinkers and brake lights work with the same power wire, one is the 'low' brightness and the other the 'high', blinkers and brake lights being the high and tail lights being the low. Hence I figured an issue with the brake light switch. I will see if there is power to the lights when pedal is depressed, but if not, it brings me back to the point I'm at, or am I missing something?

Is there a way to jump the wires in the harness at the brake light switch to see if they come on? Basically, bypassing the switch to isolate it? I found a wiring diagram here for the switch. Not good at reading them but going to try to see if I can do that. Just don't want to fry anything!

 

[pb4ugo]

Starting at either end works. Your assumption if the turns work, then so should the brake lights work too, is correct. It's been a long time since ive worked on early 40 wiring. Iir, Brake light power goes through the turn switch. When the turn switch is activated rt or left it turns off the power from the brake light circuit and activates power in the turn circuit. So 1 brake light is hot and the other is blinking from the turn circuit.

 

[jlhollowx13]

Ok, bit of an update. Went out to check power at rear. Yesterday on a drive I noticed when the brake was pressed the warning light would go off, while moving it just now I noticed it again and decided to see what the lights where doing when the warning light went out. And guess what? They are working. Everything on the rear is working as it should. Still get a warning light when the pedal is not pressed so I still have an issue somewhere, but again, this light never worked for me in the past so an issue could have been present that I wasn't aware of and I've always had little gremlins. I'm going to look into my blinker switch as it is fidgety, my parking brake switch as I have no idea if it's working, and likely replace the brake light switch.

Starting at either end works. Your assumption if the turns work, then so should the brake lights work too, is correct. It's been a long time since ive worked on early 40 wiring. Iir, Brake light power goes through the turn switch. When the turn switch is activated rt or left it turns off the power from the brake light circuit and activates power in the turn circuit.

Ok, bit of an update. Went out to check power at rear. Yesterday on a drive I noticed when the brake was pressed the warning light would go off, while moving it just now I noticed it again and decided to see what the lights where doing when the warning light went out. And guess what? They are working. Everything on the rear is working as it should. Still get a warning light when the pedal is not pressed so I still have an issue somewhere, but again, this light never worked for me in the past so an issue could have been present that I wasn't aware of and I've always had little gremlins. I'm going to look into my blinker switch as it is fidgety, my parking brake switch as I have no idea if it's working, and likely replace the brake light switch as it looks to be fairly inexpensive.

 

[Green Bean]

I believe that Coolerman has a very good writeup on brake light wiring.

 

[jlhollowx13]

A little update. I'm not exactly sure what the issue was, but possibly a dirty brake switch. I cleaned it, fixed my blinker (needed readjusted and tightened). All lights now function as intended. I do, however, have my brake warning light always on, except when the brakes are applied now. This is new. Pulling or releasing the parking brake doesn't change this. I might have an issue in the parking brake switch, or maybe the brake switch still. I'll try to narrow it down when I get some more time. Just happy all lights are working and I can drive at night now!

 

[Green Bean]

If I’m not mistaken, the dash-mounted brake light operates by the switched ground similar to the 4WD light. The hand brake switch completes the ground circuit causing the bulb to illuminate. You might check to make sure that the bulb socket isn’t grounded on the dash. Remove the socket and see if that solves the issue. If it does, you can isolate the socket from the dash with an O-ring.

 

[45Dougal]

Handbrake switch needs cleaning out id guess

 

[jlhollowx13]

If I’m not mistaken, the dash-mounted brake light operates by the switched ground similar to the 4WD light. The hand brake switch completes the ground circuit causing the bulb to illuminate. You might check to make sure that the bulb socket isn’t grounded on the dash. Remove the socket and see if that solves the issue. If it does, you can isolate the socket from the dash with an O-ring.

Thanks, I'll look at this. I'm pretty sure the blinker dash lights ground to the dash, mine seem to attach with metal clips on the bulb housing, the warning light may be different, I haven't actually looked so definitely worth it.

 

[jlhollowx13]

Handbrake switch needs cleaning out id guess

I haven't cleaned it yet so it probably needs it. I will make it a part of thr next dive into it.

 

[Green Bean]

It should be easy enough to test. I believe that the wiring harness provides a constant switched 12v to the bulb.

 

[45Dougal]

The factory manual actually has an error here so be careful. The RW side of the brake light switch should also be normally open.

You could have a short to ground, but there's an easy way to check - simply disconnect the two wires on the master cylinder (make sure that they're not touching chassis).

If the light goes out then its your parking brake switch. If nothing changes then you have a short to ground.

The switch is a folded metal case which has gaps at each corner - blast some wd40 in there and jiggle it about.

 

[jlhollowx13]

The factory manual actually has an error here so be careful. The RW side of the brake light switch should also be normally open.

You could have a short to ground, but there's an easy way to check - simply disconnect the two wires on the master cylinder (make sure that they're not touching chassis).

If the light goes out then its your parking brake switch. If nothing changes then you have a short to ground.

The switch is a folded metal case which has gaps at each corner - blast some wd40 in there and jiggle it about.

View attachment 3652866

When you say 2 wires on the master cylinder, should there be a wire connected under each reservoir?

 

[45Dougal]

When you say 2 wires on the master cylinder, should there be a wire connected under each reservoir?

Yes. There are two pressure sensors screwed into the underside and each should have a wire connected

 

[45Dougal]

The fact that the light goes out when you press the pedal suggests that the pressure sensors are connected and operating correctly... or that you have the wrong brake light switch.