Dash lights blow fuse

[Zed Head]

Also, the back of the fuse and its connections at the fuse box have a tendency to corrode and get hot.  Many 240Z's have a warped fuse cover over certain fuses.  You might check the back of the fuse box.

[Mark Maras]

 A very primitive, but effective, method to source very poor connections and short circuits is temperature. Often you can feel the heat buildup in the connection with your fingers. Be careful though, things can get hot enough to raise blisters in a very short time, especially if there's a short circuit. I usually do this test first to see if there is anything obvious. 

[siteunseen]

So true Mark, I've bubbled my fingers touching the bulbs.  1157s IIRC. 8^(

[surfsnake2]

36 minutes ago, Zed Head said:

Also, the back of the fuse and its connections at the fuse box have a tendency to corrode and get hot.  Many 240Z's have a warped fuse cover over certain fuses.  You might check the back of the fuse box.

Okay. I will check that, I really appreciate all the help, but I am starting to think I am in over my head, although at least i think i have somewhat of narrowed it down, but maybe not...(hence my lack of understanding)

Does this shed any more light: With C3 unplugged I jumped each wire, it is the GW top right wire that is causing the problem.

If i understand the diagram at all, the current is running up^ powering the speedometer, tachometer and other gauges, then going into the C3 connection block(which would explain why all the gauges have power up to this point. If this is correct where does C3 GW go after that.... If i am reading this right it goes to:

 

The A/T Indicator ???? I dont know what this is??

Then to the Radio - Which is unplugged and the fuse is pulled(Could there still be a problem?

Then to the hazard switch( I unplugged this and reconnected C3) still same problem

 

 

Edited July 16, 2016 by surfsnake2

[SteveJ]

NO! Go back to my post. Read it. It has diagnostics. Isolate. Measure. Inspect.  Most of all be patient. It takes time to type up a good diagnostic.

[Patcon]

4 minutes ago, SteveJ said:

NO! Go back to my post. Read it. It has diagnostics. Isolate. Measure. Inspect.  Most of all be patient. It takes time to type up a good diagnostic

Listen to Steve, he knows electricity!!!

[surfsnake2]

12 minutes ago, SteveJ said:

NO! Go back to my post. Read it. It has diagnostics. Isolate. Measure. Inspect.  Most of all be patient. It takes time to type up a good diagnostic.

I did read the post and I dont really understand checking branches. One of my posts/quotes was from a reply from Steve from another thread, which stated that if it was C3, then it was:

4. If so, disconnect connector C3.

5. Measure for a short. If there is no short, the problem is between connector C3 and the taillights or radio or heater control panel light or hazard switch illumination light or automatic transmission indicator light. (Note: if there is still a short, we haven't eliminated those circuits. We will confirm later.)

So doesnt this indicate the problem is one of these areas

Heater CP Light(DISCONNECTED),

Hazard Switch Lights(DISCONNECTED),

A/T Indicator light(I dont know what this is, but I have a manual so I guess I dont have one),

radio(No Fuse and DISCONNECTED)

or the taillights?????

If so arent I narrowed down to just tail lights?? But i dont understand because my tail lights are on, if C3 is unplugged shouldnt they not be receiving power? Or is this the parallel power source thing and it gets powered from multiple areas?

Edited July 16, 2016 by surfsnake2

[Zed Head]

C-1, C-2, and C-3 are all on the Green-White wire circuit.  Each one is a "branch".  SteveJ's method of measuring current would save you fuses and get you to the solution quickest, probably.  

But, another way to narrow things down would be to unplug all three connectors, then turn the light switch on.  If the fuse still blows, then you can ignore everything on 1, 2 and 3 and focus on the things not on those connectors.  If it doesn't blow, plug each connector in, separately.  Since current will be reduced with only one connector working, the fuse still may not blow.  You have to blow several fuses plugging and unplugging connectors until you find one that always causes the fuse to blow.

Your big dilemma is that you don't seem to have a dead short (low resistance) that blows a fuse a immediately.  You apparently have a high resistance short circuit.  It's flowing more current than it should but not enough to blow the fuse immediately.  That makes your problem much more difficult to solve.  If you even have a short.  You might just have too many things on the circuit and dirty fuse connections.  Dirty connections cause heat, which can be enough to melt a fuse.

Keep track of what you do and what happens.  Your observation about the dimmer switch was a good one, showing that you don't have a dead short (direct path to ground).  Write those odd things down and you'll probably realize something.

[surfsnake2]

4 minutes ago, Zed Head said:

C-1, C-2, and C-3 are all on the Green-White wire circuit.  Each one is a "branch".  SteveJ's method of measuring current would save you fuses and get you to the solution quickest, probably.  

But, another way to narrow things down would be to unplug all three connectors, then turn the light switch on.  If the fuse still blows, then you can ignore everything on 1, 2 and 3 and focus on the things not on those connectors.  If it doesn't blow, plug each connector in, separately.  Since current will be reduced with only one connector working, the fuse still may not blow.  You have to blow several fuses plugging and unplugging connectors until you find one that always causes the fuse to blow.

Your big dilemma is that you don't seem to have a dead short (low resistance) that blows a fuse a immediately.  You apparently have a high resistance short circuit.  It's flowing more current than it should but not enough to blow the fuse immediately.  That makes your problem much more difficult to solve.  If you even have a short.  You might just have too many things on the circuit and dirty fuse connections.  Dirty connections cause heat, which can be enough to melt a fuse.

Keep track of what you do and what happens.  Your observation about the dimmer switch was a good one, showing that you don't have a dead short (direct path to ground).  Write those odd things down and you'll probably realize something.

The fuse only blows when the G/W wire from C3 is connected, if it is not connected everything is fine.... I jumped every wire across C3 and the GW wire is the only one that causes the issue, as soon as i Jump/Plug it in the fuse gets hot and prepares to blow. Im not loosing any fuses over this as it is easy to see the volt/amp meter jump, I just dont know what to keep disconnecting as the post said C3 covers the radio, A/T indicator, tail lights, hazard switch and heater vent light

[SteveJ]

The SUM of the circuits is greater than the rating of the fuse. Remove part of the circuit, and you are below the rating of the fuse. Add it back, and the fuse will blow.

Before you do diagnostics, you should repair the wiring harness. If you are patient, I can make a video on how to do it. I have done it before. Repairing the harness at the combo switch will reduce some of the problem.

Here is the circuit in an overview. The white/red wire goes to the fuse box, through the 20A fuse and comes out green/blue. The green/blue wire goes to the combo switch and comes out of the combo switch when it is on as green/white.

The green/white wire branches off to the front of the car, rear of the car, and instrument panel. Each light is a parallel branch on the circuit.

In the front, the green/white wire branches off to each light, and then the circuit goes to ground. In the rear of the car, the green/white wire branches off to each light, and then the circuit goes to a ground in the rear of the car.

With instrument panel lights, the green/white wire branches off to each light and comes out red/blue. The red/blue wire goes to the dimmer, and the dimmer goes to ground.

The three pages in the FSM you need to pay attention to are BE-14, BE-16, and BE-17. These circuits are all tied to the same fuse. Note: The light behind the fan control panel is not shown.

 

Isolation of the lights.

The wiring diagrams help us to isolate the circuits so we can diagnose them. If you disconnect the C5 connector between the engine bay and dash harness, you take out the front lights.

If you unplug the connector to the ground in the back, you take out the rear lights. You may have to remove some of the trim panels to find the connector. It's been a while since I have looked for it.

If you unplug the dimmer switch, you take out the instrumentation panel lights.

Why is this important? You probably don't have a dead short (Zed Head is good with diagnostics and types faster than I can.). It appears that the sum of the current is blowing the fuse.

How can you confirm this? Isolate the different sections of the lights. (Start with isolating all 3 by how I described above.)

Method 1: Put a 10 Amp fuse in the 20 Amp socket. Turn on the parking light switch. Reconnect C5. See if you have front lights. If not, check the fuse. After testing, disconnect C5.

Next, reconnect the dimmer switch. See if you have instrumentation lights. (Make sure the dimmer is turned to maximum brightness.) If not, check the fuse. After testing, disconnect the dimmer switch.

Finally, reconnect the ground in the rear. See if you have rear lights. If not, check the fuse. After testing, disconnect the ground.

Measurement

You can also do these diagnostics with a clamp DC Ammeter or an Ammeter with a 10 Amp scale and leads with clips. If you have an Ammeter with leads, you'll need to remove the fuse. The positive lead of the ammeter will go on the inner fuse clip. The negative lead will go on the outer fuse clip. Compare the current readings to the attached spreadsheet. A number significantly higher than the value on the spreadsheet indicates a possible problem.

Inspection

For the front and rear lights, the most common culprit will be corrosion in the light sockets, especially if the lens if cracked. The corrosion makes an extra pathway between the positive and negative in the socket. It has enough resistance that it is not a dead short, but it does increase the current flow through the branch.

When I got my 260Z, the connector at the harness was in worse shape than yours. I happen to inspect the front side markers when replacing a damaged lens and noticed significant corrosion in that socket. I cleaned it with a Dremel, installed a good lens, and have not had to worry about it since.

Also, the cheater's way to fix the problem is to replace all of the bulbs with the appropriate LED bulbs. They draw 33% or less of the current from an incandescent bulb. With LEDs all around, my parking lights draw about 1A of current. I still recommend doing diagnostics and inspection before going that route.

Parking Light Circuit Calculations.xls

Edited July 17, 2016 by SteveJ
I didn't proofread to see if I left any out.

[Zed Head]

38 minutes ago, surfsnake2 said:

, I just dont know what to keep disconnecting as the post said C3 covers the radio, A/T indicator, tail lights, hazard switch and heater vent light

That's only 5 things.  I'd do the simple ones first - radio harness, heater harness, A/T indicator.  The tail lights are on the other side of the Hazard switch so things kind of re-expand on the other side of it.  You can unplug the Hazard switch but you won't know if it's the switch or the lights.  Or just do the Hazard switch first.  Down to 5, almost there.

[Dave WM]

A little late to the party, but did the OP confirm the correct lights are in the sockets? If the car has been thru a few owners someone may have decided they needed brighter lights. I would def stop now and at least fix that connector with a new one, no mickey mouse repairs to wiring.