Full Version: Gauge wiring help
Okay, when I bought my car, these gauge did not work. Upon further inspection, they were never hooked up. So, my question is, how do I hook these up and exactually where?
Anyone??
This is my only day off and want to get this fixed today. Anyone willing to help?
Okay, can anyone tell or show me (perfered) where the positive is on the alternator?
Hi,
I don't have an ammeter on my '75 914 (the gauge that says +30/-30), but I would guess there's a current shunt somewhere in the system inline with the positive terminal of the battery. The current shunt has a tiny resistance to it so as current gets pulled through it, it generates a voltage. You need to wire this voltage to the two large terminals on the +30/-30 gauge to have it register. Don't worry if you get the wires backwards the first time, the gauge will just operate in the opposite direction.
As far as the temperature gauge goes, there are three terminals at the bottom of the last picture. I'll call them top, left and bottom. The bottom one goes to the +12V supply (Red/white wire). the left one goes to ground (brown) and the top one goes to the temperature sending wire (green/black) from the oil temperature sending unit. My '75 has a black 3-terminal socket connector with these wires already attached to it. You can probably find +12V and ground somewhere there, but do you have a green/black temperature sending wire near the temperature gauge?
Regards,
Tim
I don't have an ammeter on my '75 914 (the gauge that says +30/-30), but I would guess there's a current shunt somewhere in the system inline with the positive terminal of the battery. The current shunt has a tiny resistance to it so as current gets pulled through it, it generates a voltage. You need to wire this voltage to the two large terminals on the +30/-30 gauge to have it register. Don't worry if you get the wires backwards the first time, the gauge will just operate in the opposite direction.
As far as the temperature gauge goes, there are three terminals at the bottom of the last picture. I'll call them top, left and bottom. The bottom one goes to the +12V supply (Red/white wire). the left one goes to ground (brown) and the top one goes to the temperature sending wire (green/black) from the oil temperature sending unit. My '75 has a black 3-terminal socket connector with these wires already attached to it. You can probably find +12V and ground somewhere there, but do you have a green/black temperature sending wire near the temperature gauge?
Regards,
Tim
QUOTE(TimK @ Jan 20 2008, 01:41 PM) 
Hi,
I don't have an ammeter on my '75 914 (the gauge that says +30/-30), but I would guess there's a current shunt somewhere in the system inline with the positive terminal of the battery. The current shunt has a tiny resistance to it so as current gets pulled through it, it generates a voltage. You need to wire this voltage to the two large terminals on the +30/-30 gauge to have it register. Don't worry if you get the wires backwards the first time, the gauge will just operate in the opposite direction.
As far as the temperature gauge goes, there are three terminals at the bottom of the last picture. I'll call them top, left and bottom. The bottom one goes to the +12V supply (Red/white wire). the left one goes to ground (brown) and the top one goes to the temperature sending wire (green/black) from the oil temperature sending unit. My '75 has a black 3-terminal socket connector with these wires already attached to it. You can probably find +12V and ground somewhere there, but do you have a green/black temperature sending wire near the temperature gauge?
Regards,
Tim
The temp gauge clearing tells you where to hook up which wire, but where does the engine send get connected to? The left is the sender, top is ground, bottom is 12V.
There are no wires for the temp gauge anywhere to be found.
Does anyone here know how to wire the Ammeter? I don't get it done today, it will just be another week before I can get it finished. I need help guys.
I'm looking at the Haynes manual right now to figure this out. What year is your 914? The early 914s (up to '71) had the temperature sending wire (green/black) tied to terminal 3 of the regulator plate (according to the wiring diagram). It looks like '72 had no temperature gauge. '73 and onward, the oil temperature gauge looks optional. Perhaps someone put gauges in your car from another 914 but the original car didn't have the current shunt or oil temperature sensor installed.
In my '75, the green/black wire for the temperature sending unit comes from a sensor on the right side of the engine compartment. It merges with the factory wiring harness that contains the large red wires attached to the primary 12V battery. Do you have any green/black wires on the right side of the engine compartment? Check both top and bottom sides. I removed the engine for an electric vehicle conversion, so I don't have a picture of where the green/black wire originated from...
The temp gauge clearing tells you where to hook up which wire, but where does the engine send get connected to? The left is the sender, top is ground, bottom is 12V.
There are no wires for the temp gauge anywhere to be found.
In my '75, the green/black wire for the temperature sending unit comes from a sensor on the right side of the engine compartment. It merges with the factory wiring harness that contains the large red wires attached to the primary 12V battery. Do you have any green/black wires on the right side of the engine compartment? Check both top and bottom sides. I removed the engine for an electric vehicle conversion, so I don't have a picture of where the green/black wire originated from...
QUOTE(turtleturtle @ Jan 20 2008, 11:45 AM)
The temp gauge clearing tells you where to hook up which wire, but where does the engine send get connected to? The left is the sender, top is ground, bottom is 12V.
There are no wires for the temp gauge anywhere to be found.
Here's a picture of when I dropped the engine. The oil temperature sending wire (in a '75) is near the top of the photo just under the bright red bar that holds the battery in. It has a white tag attached to it (add by me) and is green/black. Do you have one of those?
Tim
Note: I don't see the image above (I just see IPB image), so here's the URL if you need to get it otherwise:
http://bp1.blogger.com/_BC-CC9cI2Ys/RfeBo_...enginedrop1.jpg
I'm pretty sure no 914's came with ammeters. The lettering style of the gauges isn't like those in a 914 either.
To hook up an ammeter you would just put it inline with a wire. What you would use it for I don't know.
To hook up an ammeter you would just put it inline with a wire. What you would use it for I don't know.
The guages are not the stock gauges. My 914 is a 72.
There is NO wires on the right side of my car. It's not in the stock condition and was used in the SCCA here years ago before I even got it. The only 2 wires that are not connected in the engine compartment are these:
Where the heck do they go?!?!
There is NO wires on the right side of my car. It's not in the stock condition and was used in the SCCA here years ago before I even got it. The only 2 wires that are not connected in the engine compartment are these:
Where the heck do they go?!?!
QUOTE(TimK @ Jan 20 2008, 02:20 PM)
Here's a picture of when I dropped the engine. The oil temperature sending wire (in a '75) is near the top of the photo just under the bright red bar that holds the battery in. It has a white tag attached to it (add by me) and is green/black. Do you have one of those?
Tim
Note: I don't see the image above (I just see IPB image), so here's the URL if you need to get it otherwise:
http://bp1.blogger.com/_BC-CC9cI2Ys/RfeBo_...enginedrop1.jpg
You picture is not showing up. Please upload in photobucket and somewhere else.
QUOTE(jd74914 @ Jan 20 2008, 02:21 PM)
I'm pretty sure no 914's came with ammeters. The lettering style of the gauges isn't like those in a 914 either.
To hook up an ammeter you would just put it inline with a wire. What you would use it for I don't know.
I know its' not stock, I just want it to work.
QUOTE(TimK @ Jan 20 2008, 02:20 PM)
Here's a picture of when I dropped the engine. The oil temperature sending wire (in a '75) is near the top of the photo just under the bright red bar that holds the battery in. It has a white tag attached to it (add by me) and is green/black. Do you have one of those?
Tim
Note: I don't see the image above (I just see IPB image), so here's the URL if you need to get it otherwise:
http://bp1.blogger.com/_BC-CC9cI2Ys/RfeBo_...enginedrop1.jpg
I don't have that wire or any wires on that side of the engine compartment, except my electronic fuel pump.
Quoting Wikipedia:
QUOTE
There are two main wires that normally come off the battery, one extremely large one that feeds the starter, and one reasonably thick wire (usually around 10 ga) that feeds everything else in the car.
A classic style ammeter runs in series with the battery wire that feeds everything else in the car. It samples which way the current is flowing and how much current is flowing. If the alternator is pushing current into the battery (charging the battery) the gauge reads positive. If current is flowing out of the battery, it should read negative, and usually means that your charging system is not keeping up with the electrical demands.
Since the classical ammeter is hooked up in series, it involves very thick wire (like 10 ga) to be routed all the way to the ammeter in the cockpit of your car. With all that current flowing through the ammeter, a short circuit on the ammeter in the cockpit can be fairly dramatic, and some classic car guys avoid ammeters for the possibiilty of causing a fire.
There is also an ammeters out there that have an external shunt. An external shunt is basically a very low value resistor that is in series just as the ammeter was in the previous example, and then the ammeter is in parrallel to the shunt. Basically MOST of the current goes through the shunt and only a small percentage goes through the ammeter. By knowing the resistance of the shunt and the meter, the meter is able to calculate the total current by measuring only the small current that goes through the meter. This kind of setup allows small wires to be run to the ammeter in the cockpit, and the high current to remain in the engine compartment. The danger in these setups on some old cars is there isn't a fuse on that small ammeter wire, So if the shunt is damaged or a connector breaks, it would try to flow all the current through the remaining path which is the small ammeter wire and that would melt that wire (along with whatever else it is next to).
I agree that I didn't see any ammeters in any of the 914 wiring diagrams. Perhaps these were just "filler" gauges grabbed from another vehicle.
Cheers,
Tim
QUOTE(TimK @ Jan 20 2008, 02:30 PM)
Quoting Wikipedia:
QUOTE
There are two main wires that normally come off the battery, one extremely large one that feeds the starter, and one reasonably thick wire (usually around 10 ga) that feeds everything else in the car.
A classic style ammeter runs in series with the battery wire that feeds everything else in the car. It samples which way the current is flowing and how much current is flowing. If the alternator is pushing current into the battery (charging the battery) the gauge reads positive. If current is flowing out of the battery, it should read negative, and usually means that your charging system is not keeping up with the electrical demands.
Since the classical ammeter is hooked up in series, it involves very thick wire (like 10 ga) to be routed all the way to the ammeter in the cockpit of your car. With all that current flowing through the ammeter, a short circuit on the ammeter in the cockpit can be fairly dramatic, and some classic car guys avoid ammeters for the possibiilty of causing a fire.
There is also an ammeters out there that have an external shunt. An external shunt is basically a very low value resistor that is in series just as the ammeter was in the previous example, and then the ammeter is in parrallel to the shunt. Basically MOST of the current goes through the shunt and only a small percentage goes through the ammeter. By knowing the resistance of the shunt and the meter, the meter is able to calculate the total current by measuring only the small current that goes through the meter. This kind of setup allows small wires to be run to the ammeter in the cockpit, and the high current to remain in the engine compartment. The danger in these setups on some old cars is there isn't a fuse on that small ammeter wire, So if the shunt is damaged or a connector breaks, it would try to flow all the current through the remaining path which is the small ammeter wire and that would melt that wire (along with whatever else it is next to).
I agree that I didn't see any ammeters in any of the 914 wiring diagrams. Perhaps these were just "filler" gauges grabbed from another vehicle.
Cheers,
Tim
I jusat want it to be functional and not sit there and do nothing, like the temp gauge. They are there, doing nothing! I want them to work!
A 30A gauge seems useless to me . . . your alternator should put out 50-90A (I don't remember what a stock alternator does).
I could be wrong on that though. Unless you want to measure how much current your lights or stereo need.
Anyways, if you put it inline (ie: in series)in a circuit is should work.
I could be wrong on that though. Unless you want to measure how much current your lights or stereo need.
Anyways, if you put it inline (ie: in series)in a circuit is should work.
QUOTE(jd74914 @ Jan 20 2008, 02:40 PM)
A 30A gauge seems useless to me . . . your alternator should put out 50-90A (I don't remember what a stock alternator does).
Well, on that note I guess I will just stop trying to even hook it up if it needs to be higher.
First, I'm going to assume that your car runs. If your car runs, then these wires are probably for an accessory. If I look at the '72 wiring diagram in the Haynes manual and look at how thick the wires are, I'm going to guess that these wires go to the heater fan. The only other green wires go to the distributor and the alternator, which I'm assuming are already working...
Do you have a copy of the Haynes manual? I would highly recommend getting one.
Cheers,
Tim
The guages are not the stock gauges. My 914 is a 72.
There is NO wires on the right side of my car. It's not in the stock condition and was used in the SCCA here years ago before I even got it. The only 2 wires that are not connected in the engine compartment are these:
Where the heck do they go?!?!
Do you have a copy of the Haynes manual? I would highly recommend getting one.
Cheers,
Tim
QUOTE(turtleturtle @ Jan 20 2008, 12:26 PM)
The guages are not the stock gauges. My 914 is a 72.
There is NO wires on the right side of my car. It's not in the stock condition and was used in the SCCA here years ago before I even got it. The only 2 wires that are not connected in the engine compartment are these:
Where the heck do they go?!?!
In my experience, ammeters can handle somewhat more current than they actually measure. The needle tends to "peg" to one side or the other. Sometimes people just care about accuracy at lower currents (say 0-30 amps) and then just need to know (when the dial "pegs"), that the current is above +/- 30. I wouldn't put more than 50 amps through this one, though. If I were you, I wouldn't bother.
A 30A gauge seems useless to me . . . your alternator should put out 50-90A (I don't remember what a stock alternator does).
Well, on that note I guess I will just stop trying to even hook it up if it needs to be higher.
QUOTE(turtleturtle @ Jan 20 2008, 12:42 PM)
QUOTE(jd74914 @ Jan 20 2008, 02:40 PM)
A 30A gauge seems useless to me . . . your alternator should put out 50-90A (I don't remember what a stock alternator does).
Well, on that note I guess I will just stop trying to even hook it up if it needs to be higher.
The 30A range should be ok. Keep in mind that the entire alternator current is not measured by the ammeter. The ammeter should measure just the current going into and out of the battery during normal operation.
See diagrams below. For classic low impedance ammeter applications, the ammeter is directly in series with the alternator and battery. Of the 2 or more wires going to the battery, the smaller ones are for the alternator/vehicle circuits. It's these wires that the ammeter measures. For low impedance ammeters, the wire to the ammeter should be very large like 10gauge.
As the vehicle runs, the accessories/lights/ECU are powered basically by the alternator and the current to these items is not measured by the ammeter.
For high impedance ammeters, a small series resistor is placed between the alternator and the battery. Small gauge wires are run to the ammeter like 20 or 24 gauge.
You can tell if you have a high or low impedance ammeter by measuring the resistance across the ammeter. If low impedance, you should measure resistance in the tenths of ohms. This requires heavy wire routed to the ammeter. If high impedance, this one should measure more than 1000 ohms, probably much higher.
See diagrams below. For classic low impedance ammeter applications, the ammeter is directly in series with the alternator and battery. Of the 2 or more wires going to the battery, the smaller ones are for the alternator/vehicle circuits. It's these wires that the ammeter measures. For low impedance ammeters, the wire to the ammeter should be very large like 10gauge.
As the vehicle runs, the accessories/lights/ECU are powered basically by the alternator and the current to these items is not measured by the ammeter.
For high impedance ammeters, a small series resistor is placed between the alternator and the battery. Small gauge wires are run to the ammeter like 20 or 24 gauge.
You can tell if you have a high or low impedance ammeter by measuring the resistance across the ammeter. If low impedance, you should measure resistance in the tenths of ohms. This requires heavy wire routed to the ammeter. If high impedance, this one should measure more than 1000 ohms, probably much higher.
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