ammeter gauge causing fires.

[rlm2550]

So what is it EXACTLY that happens to cause fires?? Fraying wires, the gauge itself?? Just curious...
Robin

[Tatsadasayago]

The current through the ammeter causes the wires to heat up, melting the insulation and eventually causing a fire.

[rlm2550]

can it be rewired to keep the stock gauge??? Maybe heavier wires?? Trust me, I am an idiot when it comes to electricity!!
Robin

[tgreese]

The main problem is the shunt in the gauge. The meter measures the voltage drop across the shunt, which is basically a low-value resistor. Current through a resistor causes a drop in voltage which gets larger with more current... this is Ohm's law. All the charging current must go through the shunt for the meter to work. You can buy ammeters that use remote shunts, but the factory meter has an internal shunt that seems to fail with age.

When the shunt fails, the resistance increases and the amount of heat it makes increases proportionally... it's Ohm's law again. As the shunt gets hot, its resistance increases, and makes the heating worse. Since all the charging current goes through the ammeter, the increased voltage drop tells the alternator to increase its output voltage to pump more current to the battery. You can see where this is going.

Another problem - these meters were not designed, even when new, to handle the higher charging current produced by many replacement alternators. If you replace the alternator with "more heavy duty" model, you pretty much have to disable the ammeter, or you'll have a dash fire.

[letank]

Tim is the man... all the science that you wanted to know
basically oem alternator was 37amp... then 80ish amp with AC in the early 80's... with the same wires...
do the ammeter bypass, install a voltmeter

[rlm2550]

Thank you for the info!!!

[rocklaurence]

My understanding is that the meter connections become loose creating the heat and fires. An alternator doesnt push amps through the meter but by using a Difference of potential [14+- volts DC] loads electrons/holes into the battery. The resistor maybe a real issue IDk.

[79CCPathKiller]

On my 79 that's exactly what I found was that the connections were loose which loose connections create higher resistance and then in turn caused the insulation to melt off of the wires all the way down to the firewall one of them was actually melted all the way to the firewall so I had to pull the firewall plug a part find an unused plug and replace the actual spade connector that was clipped into the inner far wall and replace some of the wire that was actually on the outside of the firewall under the hood. It all started when I wanted to restore the gauges and took the dash apart. Total nightmare! Curious if anyone has a picture of how the under hood wiring harness look at the plug at the farewell. Just kind of want to see how bad mine is mangled in comparison.

[kansasboy001]

If you don't use an ammeter over 80a and make sure your conditions are tight you'll be fine. No need for a higher output unless you have a ridiculous off road h4 lighting system and a 1000w+ sound system with fuel injection

80w is more than enough with stock lighting and even an msd and a normal sound system

[Tatsadasayago]

Kansas, even stock rigs with none of those power hungry additions/alternator upgrades have had meltdowns/fires. Never say never...

[candymancan]

The wagoneers ive seen that were totaled from fires were actually grand wagoneers with volt meters. An 86 and a 88 both totaled from fires. I took pics of it too and the fires started somewhere in the dash on both Jeeps in the same exact spots. Which has always worried me about my 90. I wish i knew where these fires came from,

All I can is fix the bad wiring ive found in the Jeep, and keep a fire extinguisher handy in reach. But the fires looked like they started from the cluster/radio area. And BTW Grand Wagoneers came stock with 90A alternators. VS the 64A ones that older Wagoneers had. My 90 one of the previous owners put a new ALT in it and it was like 70A so i put in a 90A not too long ago.

One thing i noticed when messing with my fuse panel was one of the relays were extremely loose.. I mean like wobbly loose. Ill have to go back and look at which one it was but it was bigger one. And loose anything electrical causes fires am i right ? I've heard fires on these things are also caused by the blower motor the wiring starts bubbling ect.

Also Babywag told me once its from the electric choke/emissions wire shorting all the way into the cabin causing a fire. I actually looked at my orange wiring on the choke.emissions and sure enough the orange wire going to the black plunger on the throttle body i forgot its name was missing 3 inches of insulation and the wire was bubbled. I replaced the wire and added a 20A inline fuse on the emissions wiring

[rocklaurence]

Its the load that pulls amps. The alternator is a power source and wont push amps through a meter. If I were adding devices to my vehicle, I'd run them on a separate circuit [not through the amp meter] with its own fuses with a larger alternator.

[kansasboy001]

On the pre 86 the choke is fused with the backup lights and seatbelt buzzers. The other emissions wires are not fused

[candymancan]

The emissions wires on my 90 all wire together into the chike wire.. 3 orange wires into one wire.. and it deff isnt fused.. because mine was bubbled from being shorted out if it was fused it woulda poped im sure thats why i added a inline fuse on the main orange wire

[kansasboy001]

The emissions wires on my 90 all wire together into the chike wire.. 3 orange wires into one wire.. and it deff isnt fused.. because mine was bubbled from being shorted out if it was fused it woulda poped im sure thats why i added a inline fuse on the main orange wire

That was really dumb on Chrysler's part. The electric choke connector falls off so easily and shorts on the valve cover

[candymancan]

Valve cover or in my case the wire for the little plunger thing on the throttle lever i forgot its name was missing 3 inches of insultation so just the copper was exposed and where the orange insultation started it was all bubbled.. one of the 5 previous owners used electrical tape to cover them. Of course the taoe was dry rotted when i found it. If it wasnt for babywag telling me to look at the wires i wouldnt have found it.

The best part is the wire was shorting on the metal fuel line.. because you do know the metal fuel line to the carb is lile half an inch from the wire on that black thing with the nipple that pushes on the throttle lever.. thays the wire im talking about.

That orange wire wires together into the emissions.charcoal and i believe oil sending unit. The three merg together into 1 large orange wire.. crimped together with some metal clanp... wrapped in fracking duct tape.. seriously duct tape... i kid you not... seem they loved to used duct tape for electrical.

My electric choke wire was hanging off actually.. wasnt even plugged in and like you said was hanging near the valve cover and intake... im suprised between these two wires specially the one by the fuel line.. that my jeep didnt catch on fire and explode in the past.

Whats weird is.. my Carb starts the engine fine with the electric choke wires unplugged. I dont get that.. i dont even need the choke.. in summer i dont even have to step on gas pedal to cold start it either.. my carb seems to be in really good shape or something