Mystery splice to brake light switch

[Fox2506]

I discovered a wiring modification under my dash, and just wanted an opinion.

So, from the factory there are two sets of green wires leading to the brake pedal switch.

One of the plugs with two green wires is left unplugged. A splice clip has been connected to the Brown/Red heavy (heavier) gauge wire leading from the steering column/ignition. The splice leads to an in-line fuse and goes directly to the switch where the original connector was.

Why would someone do this, and might this be a common modification? Does this have something to do with making the brake lights work with no key in the ignition?

I haven't tested the original wire yet. Sometimes hitting the brakes sort of startles the electrical in the car.

[1batt4u]

I think mine is the same way since you mentioned it. I'll take a look and a picture when I can.

[marwood82]

sorry to dig up a really really old thread but does anyone know if this extra brown wire is going to the glass fuse for the brake lights?

i ask as all my brake lights and reverse lights stopped working yesterday and i have the same 'splice' for the brake switch.

i've also no fuse in slot 18 in the fuse box so i assume i must have a fuse somewhere near the pedal. (my cars not an early vin but it is one of the middle east ones).

i didnt get a chance to look at it yet, but if i follow this brown wire will i eventually find the fuse?

[Jonathan]

If there isn't a fuse in #18, wouldn't it also mean nothing is getting powered from that feed? No fuse = no circuit = no power, right?

So while there may be another inline or glass fuse somewhere up at the brake pedal for you, the +12v needs to be coming from somewhere else, and that source might have seen it's fuse blow.

Is the fuse on #16 still intact? This is shown as being dedicated for the reverse lights typically, and you mentioned those aren't working either.

[marwood82]

If there isn't a fuse in #18, wouldn't it also mean nothing is getting powered from that feed? No fuse = no circuit = no power, right?

So while there may be another inline or glass fuse somewhere up at the brake pedal for you, the +12v needs to be coming from somewhere else, and that source might have seen it's fuse blow.

Is the fuse on #16 still intact? This is shown as being dedicated for the reverse lights typically, and you mentioned those aren't working either.

yeah, i swapped fuse 16 just in case and it didn't seem to make any difference. i've also swapped all the bulbs around and they are all working.

The turn signals work fine, the parking lights work fine. the hazard lights all work ok, its just the brake and reversing lights.

i'll dig out a multimeter and see if im getting power to the switch. if i am, then if its the switch thats gone, i guess if i just stick some wire between the 2 connectors that go into the switch then the lights should come on?


it just seems odd is that they would both stop working at the same time and on both sides(given there doesn't seem to be any common electrical link between the 2). which has me also thinking its not the switches, though i guess i could have only just noticed them, but im sure they were all working on monday evening.

i'll also try pulling the plug in the harness in the engine bay and have a look at the state of the pins. could it also be a bad ground or would that kill all the rear lights?

[Jonathan]

Could someone refresh my memory on how the car's reversing switches/lights work or differ between the automatic transmission and the manual? I recall there are switches or connectors used on one and not on the other and thought this issue might be related to that. Isn't this one of those things in the car where the harness or infrastructure was ready to accommodate either transmission, and if it used it great, and if not it was just taped back or left dangling?

Marwood, what kind of transmission do you have?

[marwood82]

Marwood, what kind of transmission do you have?


manual. though it used to be an automatic .

which coupled with it being a middle east car and it having had a frame off restoration means that any attempt to apply logic to which parts should be on it doesn't really work :confused2:

[Jonathan]

manual. though it used to be an automatic .

which coupled with it being a middle east car and it having had a frame off restoration means that any attempt to apply logic to which parts should be on it doesn't really work :confused2:

Haha, the ole trifecta of unknowns :)

We'll see if someone chimes in about what you "should" be seeing in terms of reverse and brake light wiring and then go from there.

[DMCMW Dave]

It's an undocumented factory change. I believe early cars had the wiring such that the key had to be on for the brake lights to work. The second version allows the lights to run with the key on or off. The wiring diagram shows the brake lights powered by Fuse 18 which is hot all the time. Cars using the inline fuse have fuse 18 missing.

I may have the timing backwards.

Revese lights - the car harness is the same. The transmission harnesses are different.

On the automatic the switch is on the side of the trans and connected to the red plug on the bulkhead. On an automatic it's still the red plug but it also has the governor power wiring in it.

Start inhibit.

You'll also see a jumper on the red plug for the manuals, this is the starter safety switch (jumpered out on the manual, interlocked to "park" or "neutral" on the automatics.

[marwood82]

cheers for that, thats good to know. If the harness for the reverse lights is the same until it hits the transmission then i should have changed the correct fuse. (fuse 16)
as i said, im suspicious that both the reverse and brake lights seemed to stop working at the same time (and on both sides) whilst the turn signals and parking lights are fine.

if its not a fuse, which as changing fuse 16 had no effect im not convinced it is, then im leaning towards a connection/ground issue with the bulkhead connector as from what i can see this is the only point the wiring for the reverse and brake lights comes close to each other.(also this seems to be where the light cluster is grounded)
also, it would be quite a coincidence that both switches decided to fail at the same time?

i'm going to attack it with a multimeter/circuit tester over the weekend. i'll focus on the brake lights first as they are a bit more important and access to the switch is a bit easier.

the plan is

1. check that power is going to the brake light switch. (if it is then the fuse is fine)

2. connect the 2 plugs together and see if the brake lights come on. (if they do then the switch is broken)

3. if not, pull the tail light bulkhead connector, connect the multimeter to the pin for the brake lights and see if you get power when you press the brake. (this would say the connection between the switch and the engine bay is ok)

4. give the connector/pins a bit of clean, plug it back in and see if it works.

5. if not, remove one of the rear light clusters, unplug the connector to the board and check power comes through the right pin.(if it does then the board for the lights are the problem)

[jmettee]

I can confirm what Dave says about the "earlyish" cars. Mine (2075) has the fuse near the brake switch. Fuse 18 in my fuse block is absent & the cover lists it as "SPARE". Brakes work all the time, key on or off. Since the electrical schematic only documents the late design (that uses fuse 18), I don't know where power originates from for the brake switch.

You plan of attack is good for the brakes. Checking the switch wires & the engine bulkhead plug are the 2 easiest places to check for a problem then, determine which direction of the circuit you need to keep searching.

For reverse, you should also be able to pull the connectors (left side of the trans) & jumper them or probe them to look for voltage.

[dn010]

I'm so glad I came across this thread. I am diagnosing a no brake light issue also and discovered that while I do have a fuse in #18, when I look in a small mirror underneath the fuse block - there are no wires connected to the terminals.

Along with the bulkhead connector, I'd also recommend removing the tail light boards and making sure your bulbs aren't corroded and the connector terminals are not corroded as well. Good luck.

[dn010]

Does anyone have a picture of this inline fuse? I found mine, but I found it dangling - It runs from the stop light switch across the top of the steering column and then I just have the inline fuse portion connecting to nothing... Thanks in advance

[D Knight]

Dave is correct. The key had to be on and have fuse 18 installed for the light to illuminate when it left the factory. It was modded to allow function regardless of key position like other cars.


-D Knight-