Keep blowing IGN fuse, no turn sigals, gauges or, tachometer

[Da Flash]

As long the bulb is connected in place of the fuse it is in series with the load and will only light if the load present draws enough current. To be clear, no wire goes to ground from the bulb. Both wires go to the fuse clips, one for each. Most of the loads are switched after the ignition by a second switch. For example, the turn signals only turn on with the turn signal switch. If the light bulb is on when all the switched loads are off then look at the what is not switched.

The loads not controlled by a second switch are:

Charging system

Ignition system

Meters

When the car is not running the regulator sees low system voltage and tries to turn on the alternator by passing current through the field winding. The field will draw about 4 amps which is more than enough to light the light bulb. Disconnect the regulator and see if the bulb goes out.

If the points happen to be closed when the engine is not running current will flow through the coil. That is another 3 amps trying to light the bulb. Disconnect the coil positive wire and see if the bulb goes out.

The meters should not draw very much current and it is not likely the bulb will light from this load unless the problem is in these circuits.

This is a process of elemination. You disconnect on thing at a time to see if the bulb goes out. Leave each one unhooked until you find the culprit by way of the bulb behaving as expceted. To add some resolution to the process, connect a volt meter to the load side of the bulb. A true short will hold the voltage at 0 volts. A normal load will allow the voltage to rise a few volts.

Thanks for the clarification!!! I disconnected the voltage regulator and the bulb went out (Yay!!!) and yes I had the bulb hooked up outside (ground )of the bulb to the left side of the fuse holder and contact point on the bottom of the bulb (positive) to the right side of the fuse holder.

I suppose that this means that the VR is bad??(Damn, I just got a new one ~ 18 months ago from MSA!!) I'll have to look in the FSM to see if there is a way to test it for sure. For what it's worth, when I pull either of the 2 wires on the + side of the coil, the light stays on. Also I have a 280zx distributor so, I don't have points

Wouldn't you know that with my "Schleprock" type of luck, now when I hook up the battery, I get dash lights even though the light switch isn't even connected!!

I truly loathe electrical!!!

Thanks for pointing me in the right direction!!!

Edited June 23, 2013 by Da Flash

[beermanpete]

Wowsie wowsie woo woo! I remember the Pebbles an Bamm Bamm Show!

The alternator could also be the problem. Try connecting the regulator and disconnecting the alternator T-plug.

[Da Flash]

Wowsie wowsie woo woo! I remember the Pebbles an Bamm Bamm Show!

The alternator could also be the problem. Try connecting the regulator and disconnecting the alternator T-plug.

Thanks for the pearls of wisdom! When I pull the T-plug on the altenator with the VR plugged in, the light stays off. Looks like it's time to get the alt tested. I think that it might be a 280 alt with an internal VR. Strange thing is that it's been running fine for ~18 months!!

One of the many lessons learned in the latest episode of "Me and this damned Z" is, if you're blowing the "IGN" fuse, check the ignition circuit instead of what stopped working (i.e. the harness going to the tach, gauges, etc.) first!!

[SteveJ]

Internally regulated alternator with an external VR is bad mojo. It is frequently accompanied by overvoltage conditions. Going from 14.5V to 17V will result in a 17% increase in current through a circuit. A good multimeter is your friend. I hope nothing was damaged.

[Da Flash]

Wowsie wowsie woo woo! I remember the Pebbles an Bamm Bamm Show!

The alternator could also be the problem. Try connecting the regulator and disconnecting the alternator T-plug.

Ok, I finally got some time to work on the Z. I got the alt tested and it was bad, so I got a new (externally regulated ) one and still have the light turning on so, I borrowed a known good VR from a buddy and the damned light still comes one. What esle can you think of tat might have been affected by using the wrong altenator??

[beermanpete]

I don't think it would hurt anything. It just doesn't work.

Does the new alternator have output when the car is running? Does it raise the battery voltage? Does the light go out if you unplug the regulator?

Assuming everything is connected and working correctly:

The F terminal on the alternator should be 12 volts when the key is on but the engine is not running. After you start the engine the voltage at the F teminal should drop a bit. When you race the engine it should fall even more and then rise again when returning to idle. Make sure the battery is fully charged whn testing the alternator. A discharged battery will draw more current and the voltage at the F terminal will stay high.

The N terminal should be 0 volts when the key is on and the engine is not running. When the engine is runnig it shoud go to about 7 volts. As long as the N terminal is at 0 the light should be on.

[Da Flash]

I don't think it would hurt anything. It just doesn't work.

Does the new alternator have output when the car is running? Does it raise the battery voltage? Does the light go out if you unplug the regulator?

Assuming everything is connected and working correctly:

The F terminal on the alternator should be 12 volts when the key is on but the engine is not running. After you start the engine the voltage at the F teminal should drop a bit. When you race the engine it should fall even more and then rise again when returning to idle. Make sure the battery is fully charged whn testing the alternator. A discharged battery will draw more current and the voltage at the F terminal will stay high.

The N terminal should be 0 volts when the key is on and the engine is not running. When the engine is runnig it shoud go to about 7 volts. As long as the N terminal is at 0 the light should be on.

Well, I haven't been able to start the engine in a few days, I think that the issue with the ignition circuit is preventing it from starting. I have been poking around at a few connections to learn some things and see what I can find. I think that I've actually narrowed it down some. While checking some connections with my multimeter set for resistance/Ohms, I noticed that If I check the "E" or the "A" ( hell "F" + "N" too! )on altenator to body ground ( yes I was smart enough to disconnect the ground cable from the battery ) I had a closed circuit, i.e. the meter read ~002!! It did the same thing if I check resistance between the (+) battery cable and ground so after following the advice that you gave me earlier, I pulled the connectors, one at a time, in the pass footwell one at a time until I found that if I unplug the single "big white wire with no stripes", that my short between pos and gnd disappears. I isolated it to the dash side of the harness. The big white wire goes to the pos side of the ammeter, "A" on the voltage reg, the fusible link at the starter and, a 10 amp fuse at the fusebox ( not sure which one but, it's not the IGN fuse ). I disconnected the BWW from the ammeter and noticed that if I check the (+ post) to the (- post. ) on the back of the meter that there is still a short to ground.

Hopefully this isn't too long of an explanation.

Thanks for your time!!

[Da Flash]

OK, I had to give it a break and deal with that whole "work, family, non-car-related" stuff. I think that I narrowed it down to a bad gauge bulb that was causing a short to ground. While I love my 240, who came up with the 1-wire/ground to the gauge body concept??? In one of earlier post, I noticed that when I hooked up the batt neg cable that 2-3 dash lights would come on without using the light switch. So during my investigation, I noticed that the PO had spliced into the big W/R that goes from the fusebox to the engine compartment, this appears to be where some of the dash bulbs were getting power from. The bad connection/bulb was/is causing the power from the big W/R wire to jump to ground and blowing the fuse and melting the plastic connector in the W/R wire. It's been like that as long as I've has the car but, this is the 1st time that I can recall it blowing fuses!!

I've included 3 shots of the hack job that the PO perform. For clarification, the pic of the yellow wire coming off of the W/R wire is where it was spliced into. the pic of the circled Y wire and L wire with the alligator clip is the connection and lastly, the pic of the L wire and the 3 R/L wire (that go to the bulbs is where the L wire terminates).

I've confirmed that with the L wire cut, that the fuse won't blow and no more positive to negative continuity anymore.

Since I know that the L wire should get power from somewhere like a switch or the like, where should the L wire get it's power for the dash bulbs???

Edited August 1, 2013 by Da Flash

[beermanpete]

The instrument lights get power from the dimmer rheostat via a red/blue wire. The rheostat is powered from the parking light circuit via a green/white wire.

[Mikes Z car]

Beermanpete is faster than a snail!

The dash bulbs are dimmable with the dimming control so their power would come either directly from the dimming control located at the bottom of the dash above the drivers right knee or further down from the dimming control on the connection from the dimming control not going to the fuse for the parking lights. I realize this isn't all that specific.

[Da Flash]

The instrument lights get power from the dimmer rheostat via a red/blue wire. The rheostat is powered from the parking light circuit via a green/white wire.

OK, I can see from the colored diagram what you're saying, it makes sense! Now the question is where in the hell does that blue wire go??? The one that's crimped to all of the red/blue wires including the one that goes to the rheostat. The crimp point looks factory (after digging through a lot of electrical tape!)but, I don't see anything blue (with no line) in that area on the diagram.

[beermanpete]

The blue wire is the constant power to the clock. It comes from a red/blue wire that feeds several of the other accessories that work when the key is off.