Dash lights blow fuse

[siteunseen]

Google search

https://www.google.com/search?ei=6X2KV8y0A4XFmQG5nZUw&q=280z+dash+light+dimmer+switch+ground&oq=280z+dash+light+dimmer+switch+ground&gs_l=mobile-gws-serp.12...12461.18679.0.20075.11.11.0.0.0.0.417.2881.0j1j8j1j1.11.0....0...1c.1.64.mobile-gws-serp..0.9.2462...30i10.v6x7dr9i1SE

[Patcon]

I doubt it is the dimmer, some where down stream of there...

[surfsnake2]

39 minutes ago, siteunseen said:

I did a quick google search of 280z dash light blows fuse.  Here's the thread that mentions the inspection light in the engine bay also corroded side marker light sockets.

http://www.classiczcars.com/forums/topic/48516-keep-blowing-the-fuse-for-the-dash-lightstail-lightspark-lights-please-help/

unhooked the engine light, still same issue.

I did notice that as i turn the dimmer switch up to 100%(slowly)  @ approximately 80% the ampmeter gauge jumps significantly and all of the parking lights dim to about 10%. (I dont know if this helps or just adds more confusion)

[Patcon]

I believe the dimmer has just 2 wires, correct? If so unplug and stick a jumper wire across it. If the fuse blows it's not in the dimmer. If the fuse holds and the dash lights are on and all the way up, the dimmer is bad...

[siteunseen]

If that dimmer works like a potentiometer I think I would try spraying some CRC electrical cleaner first. Then pull it and sand the wrapped wiring.

[surfsnake2]

Good news, i at least have narrowed it down

From another post:

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.)

I tried this and the voltmeter didnt peg and the dash lights were at 100% so i will start seeing what happens now

 

[siteunseen]

2 minutes ago, Patcon said:

I believe the dimmer has just 2 wires, correct? If so unplug and stick a jumper wire across it. If the fuse blows it's not in the dimmer. If the fuse holds and the dash lights are on and all the way up, the dimmer is bad...

There you go!  Sounds like a good idea to me.

[siteunseen]

3 minutes ago, surfsnake2 said:

Good news, i at least have narrowed it down

From another post:

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.)

I tried this and the voltmeter didnt peg and the dash lights were at 100% so i will start seeing what happens now

 

Read, read, read!  Every problem I've ever had has been documented over the 40 years of these cars. 8^)

[surfsnake2]

So... Weird, I left C3 unhooked for a bit with the dash light on, and everything was fine.

Plugged C3 Back in, And Everything was still Fine....... I thought Christmas Miracle? No, wrong month.... Because about 20 seconds later, without having done anything the dash lights dropped, the voltmeter pegged.

Any ideas of why it would be fine after plugging c3 back in and then all the sudden a drop 20-30 seconds later?

 

 

Also is there a way to isolate c3 down to the wire?

I am trying to follow the FSM, and I guess I am not doing very well, because It seems like the dash lights would go out when I unplug C3, but they stay on and are working well, and the tail lights are on also. The radio is unplugged(and i even removed the fuse) and so is the heater/vent light... The hazards work, except they dont light up on the tachometer so i am having trouble understand what C3 controls?

Edited July 16, 2016 by surfsnake2

[Patcon]

Maybe one of our resident engineers will chime in but my understanding of fuses is they are heaters in reverse. Pull too much current and they heat up which melts the element breaking the circuit. If the over current is small it takes longer for the fuse to reach melting temperature before it let's go...

[SteveJ]

 

21 minutes ago, Patcon said:

Maybe one of our resident engineers will chime in but my understanding of fuses is they are heaters in reverse. Pull too much current and they heat up which melts the element breaking the circuit. If the over current is small it takes longer for the fuse to reach melting temperature before it let's go...

There are parallel paths for current.

IT=I1+I2+I3

When C3 was disconnected, one path was removed. When the dimmer was cranked up or removed, one path was removed. All paths together make enough current to blow the fuse.

Easy way to diagnose: Use a clamp ammeter (https://www.amazon.com/gp/product/B009CNYJG2) to measure the current on each branch (front, dash, rear) while they are isolated from the others. While noting what lights are on, you can estimate the current. The bulb wattage is in the FSM.

You probably have one or more exterior sockets with corrosion. That can increase the current draw.

Before you do the testing, you might want to fix the wiring harness at the headlight switch. Vintage connections (http://www.vintageconnections.com) has a perfect replacement 9 pin connector. Been there done that. Unfortunately that site is down right now.

I'll do a follow-up post on how the break down the circuit for testing.

[Zed Head]

I think that's a good analogy.  Also why more fuses blow when it's really hot out.

Take a look at this fragment of a diagram I copied.  The GW wire that gets hot feeds many small lights.  Any single one of which could be your short.  It also shows why C-3 didn't turn everything off.  I put a red dot next to each branch.  I think that you were on the right track by unplugging things.  You just need to keep unplugging until the problem goes away.  Here's one diagram source, a GIF file from atlanticz - http://atlanticz.ca/zclub/techtips/electrical.htm

I used the pdf version from here -  http://www.nicoclub.com/FSM/260z/1974/