Let's play: Guess the electrical gremlin in the Gremlin!

[ridered777]

I found the problem!

Originally Posted by Elliott

Ok, I have a 1975 AMC Gremlin.

[Elliott]

Originally Posted by benebob

No a diode resitor pack in after the idiot light before it goes to the other items on the circuit.

Nope, there is nothing like that. Which if there were a diode between the idiot light and the rest of the cluster, the gauges wouldn't have worked at all, instead of just reading low.

Originally Posted by MadMaxSvx

Oh, of course..! You switched the wires in the alternator, thats why the light remained off when engine off but swith in ign position, and on when engine running.

No, the alternator was properly connected the whole time.

The problem was more cluster related.

[MadMaxSvx]

NO? Let me guess, the problem was the meter fuse, or the cluster ground, or a broken ring, or a flat tire, or... i quit!!

PS: Really, it wasnt a gremlin eating your wiring?

[Elliott]

Originally Posted by MadMaxSvx

Let me guess, the problem was the meter fuse

Yep, it was the fuse to the cluster, must have blown it when the original alternator went out.

I didn't expect it because the gauges and idiot lights still kinda worked. I looked over the schematic in my service manual and saw it was possible for power to back feed from voltage regulator of the alternator through the idiot light and power up the gauges and since this idiot light was before them in this backwards circuit and adding resistance, they would read lower than normal, but they wouldn't work at all when the engine was not running.

The way the idiot light works is there is normally 12 volts supplied to one lead of the bulb from the cluster when the switch is on and the alternator is also supplying 12 volts to the other lead when it is charging, so the light stays off because there is no ground. When the alternator isn't charging, it becomes the ground, so the light comes on. My light was working backwards because the alternator was supplying the voltage and it found a ground through the rest of my gauges.

Makes perfect sense now, but a blown fuse was one of the last things on my mind until I looked at the schematic.

[MadMaxSvx]

Originally Posted by Elliott

Yep, it was the fuse to the cluster, must have blown it when the original alternator went out.

I didn't expect it because the gauges and idiot lights still kinda worked. I looked over the schematic in my service manual and saw it was possible for power to back feed from voltage regulator of the alternator through the idiot light and power up the gauges and since this idiot light was before them in this backwards circuit and adding resistance, they would read lower than normal, but they wouldn't work at all when the engine was not running.

The way the idiot light works is there is normally 12 volts supplied to one lead of the bulb from the cluster when the switch is on and the alternator is also supplying 12 volts to the other lead when it is charging, so the light stays off because there is no ground. When the alternator isn't charging, it becomes the ground, so the light comes on. My light was working backwards because the alternator was supplying the voltage and it found a ground through the rest of my gauges.

Makes perfect sense now, but a blown fuse was one of the last things on my mind until I looked at the schematic.

Next time, the first thing to check are the fuses!

[Trevor]

Originally Posted by Elliott

Yep, it was the fuse to the cluster, must have blown it when the original alternator went out.

I didn't expect it because the gauges and idiot lights still kinda worked. I looked over the schematic in my service manual and saw it was possible for power to back feed from voltage regulator of the alternator through the idiot light and power up the gauges and since this idiot light was before them in this backwards circuit and adding resistance, they would read lower than normal, but they wouldn't work at all when the engine was not running.

The way the idiot light works is there is normally 12 volts supplied to one lead of the bulb from the cluster when the switch is on and the alternator is also supplying 12 volts to the other lead when it is charging, so the light stays off because there is no ground. When the alternator isn't charging, it becomes the ground, so the light comes on. My light was working backwards because the alternator was supplying the voltage and it found a ground through the rest of my gauges.

Makes perfect sense now, but a blown fuse was one of the last things on my mind until I looked at the schematic.

You deserve being pleased with yourself. You carefully analysed what was in technical jargon a sneak circuit, somewhat akin to that which which results in the Christmas tree" episodes.

[Elliott]

Originally Posted by Trevor

You deserve being pleased with yourself. You carefully analysed what was in technical jargon a sneak circuit, somewhat akin to that which which results in the Christmas tree" episodes.

It is easy when your entire car's wiring diagram fits on about 5 8.5x11 pages, the SVX's diagrams scare the hell out of me and I have some gremlins to work out in mine.

[benebob]

Originally Posted by Elliott

Yep, it was the fuse to the cluster, must have blown it when the original alternator went out.

I didn't expect it because the gauges and idiot lights still kinda worked. I looked over the schematic in my service manual and saw it was possible for power to back feed from voltage regulator of the alternator through the idiot light and power up the gauges and since this idiot light was before them in this backwards circuit and adding resistance, they would read lower than normal, but they wouldn't work at all when the engine was not running.

The way the idiot light works is there is normally 12 volts supplied to one lead of the bulb from the cluster when the switch is on and the alternator is also supplying 12 volts to the other lead when it is charging, so the light stays off because there is no ground. When the alternator isn't charging, it becomes the ground, so the light comes on. My light was working backwards because the alternator was supplying the voltage and it found a ground through the rest of my gauges.

Makes perfect sense now, but a blown fuse was one of the last things on my mind until I looked at the schematic.

See if you would've had that diode/resistor pack my TVR has which prevents back feeding you wouldn't have had this problem. Nothing would have worked.. K.I.S.S. is the philosophy I preach concerning electrical gremlins, one of these days I'm sure to listen to it too.

[Trevor]

Originally Posted by Elliott

It is easy when your entire car's wiring diagram fits on about 5 8.5x11 pages, the SVX's diagrams scare the hell out of me and I have some gremlins to work out in mine.

If the auto industry produced true schematic drawings as well as wiring diagrams, there would not be a problem.

[Hondasucks]

Originally Posted by Elliott

It is easy when your entire car's wiring diagram fits on about 5 8.5x11 pages, the SVX's diagrams scare the hell out of me and I have some gremlins to work out in mine.

You think that is scary? The EWD (Electrical Wiring Diagram) book for the 2010 Toyota Camry is like, 300 pages! (The book is like 2 inches thick. It's really scary when you hold it next to the complete service manual for my 68 Polara, and it's the same size...)

[Elliott]

Originally Posted by Hondasucks

You think that is scary? The EWD (Electrical Wiring Diagram) book for the 2010 Toyota Camry is like, 300 pages! (The book is like 2 inches thick. It's really scary when you hold it next to the complete service manual for my 68 Polara, and it's the same size...)

I think the SVX is about as complex as I want to get into. Even it is a little out of the ordinary for me, not much newer than the 1980s catches my eye. I'm more into the 1950s and 1960s stuff.

I'm going to have to draw my own wiring diagram as I build my 1959 Rambler American, it is going to get a 1996 Land Rover 4.0L (direct relative of the 1960s Buick 215 V8) with the EFI. It isn't the first car I have wired from scratch, my first was my 1966 Mustang, but it will by my first time with EFI.