Keep blowing the "IGN" fuse!!!

[Zed Head]

Not sure that you understand what resistance is. When you disconnect the gauges you wouldn't get rid of resistance, you would create infinite resistance (ignoring the conductivity of air). "No resistance" would be a very very small number or a zero on your meter. High resistance, or "some" resistance would be a number from typically 60 to 1,000's of ohms for most of the tings you'll measure on your car. Infinite resistance would be what you get with the meter probes touching nothing at all, just air.

You really need a meter that you understand to get good measurements. The cheaper, or older, meters have an adjustment knob on the face. After you pick the range, you touch the probes together and move the knob until it shows zero. Then you know what "no resistance" looks like. If you have a small light bulb, like a dash bulb, handy you can take a measurement on it to see what "some" resistance looks like on your meter, with one probe on the center electrode on the bottom and the other probe on the shiny metal side of the bulb. A typical bulb will measure about 4 ohms.

You need to get good resistance numbers, and know what the proper range of resistance is for what you're measuring. Some resistance is good, it's how things work.

[beermanpete]

It's been a while since I've had time to work on this. I'm not so sure it's not the gauges. Following the advice given in this thread, the only things that I can disconnect and get rid of the resistance are the gauges. It has something to do with the gauges being installed/grounded to the dash. I can connect all 3 gauges and get no resistance as long as they're not grounded. I also find it odd that with the gauges installed in the dash, I can get resistance to ground reading on all the pins at the connectors for the 3 gauges (oil/temp, amp/fuel, and tach) I realize that the black wire is a ground but, I find it hard to believe that all the wires go to ground!!

Ok. So now you need to install the gauges one at a time to see which one causes the problem.

The Mastech meter you are using is not autoranging. This means you need to select the correct resistance range for what you are measuring. When you get the "1" reading on the 2k range it does not mean you have an open circuit, it means the resistance is larger than 2000 ohms. Try selecting the higher ranges to see if you get a reading. Also, when the reading is .057 or some other low number (below .200) you can select the 200 range and get better resolution.

[Zed Head]

beerman, since you know the Mastech, can't he just get the probes where he wants to measure and turn the knob until he gets an in-range reading? Then re-zero, if he needs to.

I've been spoiled by my auto-ranging meter which also reads negative. But I bought it because my old Micronta meter wouldn't calibrate to zero anymore.

[Da Flash]

Ok. So now you need to install the gauges one at a time to see which one causes the problem.

The Mastech meter you are using is not autoranging. This means you need to select the correct resistance range for what you are measuring. When you get the "1" reading on the 2k range it does not mean you have an open circuit, it means the resistance is larger than 2000 ohms. Try selecting the higher ranges to see if you get a reading. Also, when the reading is .057 or some other low number (below .200) you can select the 200 range and get better resolution.

Thanks for the reply! I've tried removing each of the 3 gauges 1 at a time and they all give readings. Most of the readings that I am getting are below the 200 range so, I set my meter to 200. Here are the readings that I get at the connector with each of the gauges installed

Amp/Fuel

black wire=00.4

Y/R=59.0

Y=105.0

Oil/Temp

Black=03.3

Y=108.1

Y/R=62.1

Y/Bl=106.8

Tach

Black=55.6

Y/R=.459 (meter set to 2K)

Both White wires=1.___ (on these 2 I used all of the ranges and couldn't get anything)

While I have these readings, I don't know what they are supposed to be!! How can I tell if the gauge(s) is/are bad??

[beermanpete]

beerman, since you know the Mastech, can't he just get the probes where he wants to measure and turn the knob until he gets an in-range reading? Then re-zero, if he needs to.

I've been spoiled by my auto-ranging meter which also reads negative. But I bought it because my old Micronta meter wouldn't calibrate to zero anymore.

I don't know the Mastech either. I looked it up on the internet and found the owner's manual. This meter does not have a zero knob for the ohms.

[beermanpete]

Thanks for the reply! I've tried removing each of the 3 gauges 1 at a time and they all give readings. Most of the readings that I am getting are below the 200 range so, I set my meter to 200. Here are the readings that I get at the connector with each of the gauges installed

Amp/Fuel

black wire=00.4

Y/R=59.0

Y=105.0

Oil/Temp

Black=03.3

Y=108.1

Y/R=62.1

Y/Bl=106.8

Tach

Black=55.6

Y/R=.459 (meter set to 2K)

Both White wires=1.___ (on these 2 I used all of the ranges and couldn't get anything)

While I have these readings, I don't know what they are supposed to be!! How can I tell if the gauge(s) is/are bad??

When you took these measurements how did you connect the ohmmeter? Was one lead on the greem wire at the fuse block for all of these reading and the other lead on each wire in your list?

[Da Flash]

When you took these measurements how did you connect the ohmmeter? Was one lead on the greem wire at the fuse block for all of these reading and the other lead on each wire in your list?

Sorry about the confusion. All of these readings are at the connector pins on the back of the gauge(s) to ground (the metal dash frame). I might also add that the harness is disconnected from the gauge(s).

[beermanpete]

Thanks for the reply! I've tried removing each of the 3 gauges 1 at a time and they all give readings. Most of the readings that I am getting are below the 200 range so, I set my meter to 200. Here are the readings that I get at the connector with each of the gauges installed

Amp/Fuel

black wire=00.4

Y/R=59.0

Y=105.0

Oil/Temp

Black=03.3

Y=108.1

Y/R=62.1

Y/Bl=106.8

Tach

Black=55.6

Y/R=.459 (meter set to 2K)

Both White wires=1.___ (on these 2 I used all of the ranges and couldn't get anything)

While I have these readings, I don't know what they are supposed to be!! How can I tell if the gauge(s) is/are bad??

Sorry about the confusion. All of these readings are at the connector pins on the back of the gauge(s) to ground (the metal dash frame). I might also add that the harness is disconnected from the gauge(s).

Ok, thanks. These readings look fine. There is no short and none of these readings indicate a condition that would blow a 20 amp fuse.

You have said that when you install the gauges the fuse blows and when you remove them the fuse does not blow. The only thing I can think of to cause this is when the ammeter/fuel gauge is removed there is no power to the entire car and therefor no current can flow to blow the fuse regardless of where the short is. To test this try connecting only the ammeter (the large white wire and the large white/red wire) leaving all the other wires for the fuel gauge and other gauges disconnected and see if the fuse still blows.

[Da Flash]

Ok, thanks. These readings look fine. There is no short and none of these readings indicate a condition that would blow a 20 amp fuse.

You have said that when you install the gauges the fuse blows and when you remove them the fuse does not blow. The only thing I can think of to cause this is when the ammeter/fuel gauge is removed there is no power to the entire car and therefor no current can flow to blow the fuse regardless of where the short is. To test this try connecting only the ammeter (the large white wire and the large white/red wire) leaving all the other wires for the fuel gauge and other gauges disconnected and see if the fuse still blows.

thanks for your reply I'm going to reinstall the dash and try your experiment to see what I get. I was trying to avoid a bunch of removing and reinstalling the dash. Is it normal to get a resistance to ground on all of those gauge wires? I was under the impression that there should only be resistance between ground and the ground wires.

[beermanpete]

thanks for your reply I'm going to reinstall the dash and try your experiment to see what I get. I was trying to avoid a bunch of removing and reinstalling the dash. Is it normal to get a resistance to ground on all of those gauge wires? I was under the impression that there should only be resistance between ground and the ground wires.

Yes, it is normal to have a resistance reading from the positive terminal to the negative terminal (ground.) It is through this resistance that current flows and the device works. What we are looking for when testing with an ohmmeter is the correct amout of resistance, whatever that may happen to be.

[Da Flash]

Yes, it is normal to have a resistance reading from the positive terminal to the negative terminal (ground.) It is through this resistance that current flows and the device works. What we are looking for when testing with an ohmmeter is the correct amout of resistance, whatever that may happen to be.

Ok, I got a chance to install the dash and hook everything up but the meters. I was reading an old thread that we were involved with earlier (http://www.classiczcars.com/forums/electrical-s30/49746-keep-blowing-ign-fuse-no-turn-sigals-gauges-tachometer.html) and I think the short is somewhere else. The only thing that I have found that I disconnected and will not light a 1156 bulb in place of the "IGN" fuse is the voltage regulator. I've replace it, but the light remains.

[Da Flash]

I am going to install an internally regulated altenator and the harness plug w/diode to eliminate the regulator altogether and see if that can keep the bulb unlit.