Ignition fuse behaving like a resistance?

[Agustin Alfonso Cesar Charles]

Guys, good morning, just a general question about fuses.

Recently I revisited my charging system (while engine running) to find out 14.3V at the ALT and 13.2 on the rest of the under hood fuse box. After some paint removing and putting cables metal – to – metal, now the fuse box reads 14.3v too (bad grounds mainly). Now I am looking at the under dash fuse box. Some fuses have 13.2 and others 13.9. But, checking the feed of the fuses (while engine off and comparing the 12.6 reading of the under hood fuse box), the feed reads 12.6v, and I don´t know why am I loosing power on the fuse. After a drive the ignition fuse is warm, more like normally warm that weirdly warm (it controls almost everything on the car) but not hot, and show a drop of 1.26 volts and I don´t know why. I exchanged the fuse with other in the fuse box and has the same behaviour, being me just a DIY average guy and unable to apply my computer skills to a carbureted car 😛 I am googling around trying to understand if that (20 amps btw) fuse is bad or the circuit is overloaded.

And yes, is the same Swift / Metro with the weber carb and the electric choke. The circuit is still in its original state, it feeds the following: fuel pump, ignition coil, power windows, turn signal, A/C feeds, Radio feed, ALT signal, even the Reverse lamp, almost everything. Unplugging the fuse leaves the car dead, the only thing that works is the starter and the head / tail lights 😛

Could I be overloading the circuit? bad wiring? bad fuse?

I do remember I fixed a problem with the choke heater element that blew a diode used to feed the fuel pump, I had to install a relay feeded from the coil to get the signal but besides that everything ran fine. And both the MSD coil and the Weber carb were installed at the same time, but never checked at that time the voltage.

Oh, I remember something, I also installed a temp gauge that had a feed from the coil wiring too, and the needle drops and reads lower every time I use the power windows, A/C, head lights, reverse, turn signals (it drops in every click of the signal). It has behaved like that since I installed it, long before the carburetor and coil upgrade.

Topic

[college man]

You could be getting a voltage drop from corrosion at the wire or in it. You could also
be getting a voltage drop from the temp gauge or ignition coil. Try disconnecting the
temp gauge to see if voltage comes up. If so increase the wire size.

[Agustin Alfonso Cesar Charles]

Will do.

Now, just to be prepared, when you say “increase the wire size”, you mean the wire that feed the ignition fuse to the fuse box?

I was also thinking, what if I setup a relay? so that the ignition signal activates the relay from the fuse side that get energized, and then the relay feeds power from the under hood fuse box that has 14V to the fuse side that feeds the systems? all this using the existing fuse conector. I was thinking about that option today so that I don´t mess with the wiring, the problem I have is where to put a fuse between the relay and the fuse box. Also I don´t know if I am breaking some electric rule that may compromise the whole electrical system.

[Charles]

If the fuse is getting warm it is obviously under load and will drop some voltage. The most important consideration is the battery and ignition voltage. The battery should receive a nominal 13.6 Volts from the alternator if it is fully charged. The loss between the alternator and the battery can be attributed to either heaver than normal load or bad connections. Some circuits in the fuse box will have slightly different voltages account the actual load on the circuits.

[college man]

[quote=”CarDoog” post=162040]Will do.

Now, just to be prepared, when you say “increase the wire size”, you mean the wire that feed the ignition fuse to the fuse box?

I was also thinking, what if I setup a relay? so that the ignition signal activates the relay from the fuse side that get energized, and then the relay feeds power from the under hood fuse box that has 14V to the fuse side that feeds the systems? all this using the existing fuse conector. I was thinking about that option today so that I don´t mess with the wiring, the problem I have is where to put a fuse between the relay and the fuse box. Also I don´t know if I am breaking some electric rule that may compromise the whole electrical system.[/quote]

I was thinking was the temp gauge wire or the msd coil. Thats why I wanted you to
unplug the gauge or the coil to see if voltage is restored.

[Agustin Alfonso Cesar Charles]

I unplugged the sensor and noticed a newbie mistake that I believe I made 3 years ago (long before I even started to watch ETCG.

From the Feed that energizes the coil I had:
Fuel pump (both signal AND feed), temp sensor feed, choke heater element feed, and coil.

Yes, all those elements SHOULD (maybe not the coil) be feeding from a relay, not fr the signal wire that comes from the ignition key.

Rewired everything to a relay that feeds from a junction block that goes from the alt to the battery. And the signal feed “signals” that relay only, and the coil.

It was an old installation I made before knowing anything about cars or ETCG, or even YouTube. Now that I think about it, that little wiring hold a lot of current, just to drive the fuel pump, now I know why I was getting so little voltage, I had too many fat loads on that little cable. Even the wire size was small, I don’t know why I didn’t noticed at the time.

The voltage now is 13.76 and rising. Still thinking to move the coil to a dedicated relay but don’t know if it’s necessary since the original coil was also like that.

For best performance should I install the coil with a relay and unload more that circuit?

[college man]

I’m gonna say having the feed and signal together was causing some drop.
Lets see how she acts for now and we can always go further if we need to. 🙂

[Author]

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