Fuse Block Question

[coopdog240]

Car is a 240Z - 10/70 build date (Series 1)

What is the circuit marked "common" on the lower right of the

fuse block (shown with white arrow in photo) for? Does a fuse belong in this slot?? If so, what amperage?

Edited July 16, 2011 by coopdog240

[SteveJ]

It is for the accessory circuits. It is 20A, just like it is labelled on the circuit board.

[rupertjab89]

I have a 71 240z, i believe it's a series II (build date 8/71), and my fuse panel looks much different. I have the round fuses... "the common is for the accessories"... but what does it do for the accessories? is it supposed to be a wire type fuse or a ... flat filament? type of fuse.

i recently had a bad dome light experience. the switch for the dome light overheated, and almost started on fire in my car, and the "common" fuse finally broke after we saw smoke, so that was interesting.

any tips would be wonderful.

[SteveJ]

Rob, the OP installed a replacement fusebox from Motorsport Auto. That's why he has the newer style fuses.

The issue that you have is a short to ground. It could be at the switch or in the wiring nearby. If I were to speculate, at first it wasn't a very solid contact. As the current flowed through the circuit to ground, the switch or a wire nearby started to heat up. (Think of the inside of a toaster.) Insulation melted/burned causing the smoke you saw, exposing more of the component to the ground fault. The increased contact with ground increased the current flow to the point that the fuse finally blew.

If it was a door switch, replace it. If it was the switch on the dome light, replace the dome light. Be sure to inspect the wiring near the dome light or door switch for damage. If it is the door switch, verify good wiring by doing the following.

1. Remove the lightbulb from the dome light and accessory fuse.

2. With the door closed, measure resistance from the downstream side (outside) of the accessory fuse to ground (any exposed screw that goes into the body of the car will do). You should have infinite resistance. (maximum value on your meter)

3. If you have less than 1 ohm resistance, then you have a short between the fusebox and the switch to include the switch. Unplug all wires from the switch and try again.

a. Be sure to mark wires to put them back the same.

b. Be sure to look for any burn marks around those wires or on the body. That's another sign of a short. Someone could have left part of the connector exposed when plugging in the switch, allowing for the exposed part to touch the body.

If you have infinite resistance, the switch is bad. If you still have less than 1 ohm, you have a short in the wire.

4. If you still haven't found a short, with all of the wires unplugged from the switch, test each wire on the switch to ground.

5. If you have ruled out the switch, test all of the dash harness side wires for the switch to ground.

Be sure to go to the XenonS30 site and find the supplement for the 1971 FSM. It will have a lot of information on the wiring.

Get to work and let us know your results.

[rupertjab89]

So some fun things happened (exciting i guess, maybe not fun)

1. the dome light shorted out and started a minor electrical burn. luckily my dad and i caught it in time, now it just stinks.

2. some grounds were terribly bad, so we cleaned up the terminals and put them back.

3. the turn signal sockets were not getting ground. i had to pull some off a 2000 altima and cut a tab off, but they fit pretty good with a little permatex

4. i replaced a lot of fuses (some were the incorrect amp)

5. the PO had an aftermarket stereo hack/slash install, so the center wires were really mashed/confusing because soo many wires were tapped in where ever the PO could pull power

6. everything works now, gotta make a couple of the new ground wires prettier and replace a couple fuses yet.

another question, there is still heat in the fuse block on one fuse. does this signal a minor short occuring that i should be looking for yet?

[SteveJ]

Which fuse is heating up? It could be caused by the addition of parallel branches on the circuit or a short created by corrosion.

[rupertjab89]

Park. Tail is heating up. The tail lights were in great shape, but the parking lights (the lower one's, the combo park/turn signal lights), were the one's we were messing with. You're saying if I add parallel circuits, it causes a higher strain on the system?

[SteveJ]

That is not an usual circuit to have problems. Go to Motorsport Auto and order the parking light relay kit. It was designed and built by Dave Irwin, aka Zs-ondabrain on this website.

To see why parallel circuits would increase the current through the fuse, look at this example.

[EScanlon]

Sorry, but I disagree.

The Parking Light Relay will NOT fix this problem. It will only mask the faulty condition for a while by diverting the current from the car's existing circuits to a secondary circuit AFTER the car's fuse. Yes the fuse problem will be "solved" but the inherent PROBLEM will only be exacerbated. While the problem may be in the combination switch and connections, the relay kit does NOT get rid of the problem.

The Relay is designed to reduce the current loss to the lights due to the switch and other connections up at the steering column by connecting power DIRECTLY from the battery into the wiring AT the steering column and to the Parking Lamps. It does not REPLACE the wiring to the park lamps, it uses the EXISTING wiring, which is probably what is currently having problems.

If the wiring is at fault (as it stands now) all you are doing is putting in a larger source of current to a poor set of "pipes".

Can you say.... Melt Down???

The problem that MUST be fixed FIRST, is to determine WHY and HOW you have resistance in the wiring. To simply assume that it needs additional "pressure" behind it is analogous to putting a larger capacity fuel pump on leaky fuel lines figuring that the extra capacity will overcome the loses due to the leaks.

Check the BASICS first.

Look at all the bulbs, see if there is corrosion in the bulb connectors. Check the wire connections. Determine if your lamps are the ones that require grounding to the body and check that they ARE getting good grounds. Check the ground connections, clean them off anyway when you replace the wire.

Clean the fuse box clips, check that the fuses are actually good.... heck for a few bucks replace them. If they're old fuses the chances of the internal connections being partly at fault are good.

The "just slap this into it" obviates basic troubleshooting / maintenance techniques and fools us into thinking the problem has been solved... it hasn't.

FWIW

E

[SteveJ]

E, I misread part of his post. I thought he said he cleaned the sockets. Part of the problem is that the wire is on the small side for the current load going through it. IMHO the fuse should be 10A instead of 20A. That would better protect the wire. Yes, corrosion will make current draw worse since the corrosion can create a short circuit when it becomes so extensive that it breeches the gap between the positive contact and ground. However, from his description he chose to implement unique engineering solutions into a car where a previous owner apparently went to town already on the wiring.

I would agree that the best way to test the system would be to take current reading on all branches, provided the wiring hasn't been hacked to a point where there are unknown parallel branches causing the overload. Most people (and I'm sorry if I offend Ron by including him in this group) don't know much about current measurements. It doesn't seem like he followed my earlier diagnostics that would have required the use of an Ohmmeter to track down his short.

Having been victimized by the parking light circuit in both of my cars, I decided that the best course of action for myself would be to clean the sockets and substitute LED bulbs. I mentioned the parking light relay harness because it will give Ron the time to diagnose further without burning up his fusebox. Unfortuntately it sounds like he is close to burning it up already.

[rupertjab89]

Ron? Who's Ron? Hi, I'm Rob.

My dad and I haven done EXTENSIVE following of wires and grounds and current checking and voltage checking on many wires and connections and everything.

The wiring has been hacked up and messed with by at least one previous owner. The dash wiring is awful because someone must have REALLY needed their stereo wired up and pulled power and switched grounds around wherever they could. It was so bad I simply pulled the stereo and speakers and have no desire to fix THAT problem right now, instead focusing on the drivability of the car.

Knowing that someone liked to mess with wiring before I got to it, tracking the actual problem in the harness in the engine compartment was a large chore.

In order to make less work, (we both hate wiring), is there a place to get a new wiring harness for this old of a vehicle, or would i be stuck rebuilding/wiring the harness?

I'm guessing there are multiple wires drawing excessively on the system (corroded due to poor storage). I still need to get my ignition checked out too, another problem of it's own.

The wiring is a cluster all around on this car, and so, is there a place I can get new harnesses and start fresh, or is that something no one does?

[SteveJ]

You're now officially Ron. We'll also periodically change your name to keep you confused.

No one that I know of is manufacturing reproduction harnesses. You could try to adapt a Painless kit or get a used harness from Z Car Soure, Zbarn or Z Specialties. Don't expect used wiring harnesses to be perfect or cheap. You can get many different types of replacement connectors from Vintage Connection. When getting a used wiring harness, try to get one from a car with a similar build date to yours. If the wiring harness has a part number, contact Mike to buy a CD of the parts manual to find the part number appropriate for your car.

If I was given a choice between 3 Z cars, one with a bad body, one with a bad motor, and the third with bad wiring, I'd probably take the one with the bad motor. I'm not even that good with engines, either.