the fuel gauge and oil pressure gauge on my 1978 are not working. the needles are all the way to the right. im thinking that it is a ground problem. im not sure where to start.

 

You should pull the center cluster and check the fingers where the plug is connected.

The gauges do not have a dedicated ground per say.

The fuel gauge has a dedicated wire which is the fourth wire down in the plug on the passenger side. The temperature gauge has a dedicated ground and is the first wire on top of the connector on the driver’s side.

The Amp Gauge and oil pressure gauge ground to the housing.

I think you might have a loose finger on the back of your printed circuit board and it may be putting power on the ground side of the gauges. I’m not sure.

Lack of ground on the gauges would make them not function at all instead of peg. Missing ohms input would not work the same on all gauges. (Example, a temp gauge missing ohms signal would read cold, while a fuel gauge would read full),

The most common problem on this year car is usually a problem in the printed circuit and the fingers where the connector plugs in. If one is loose you can simply re-glue it down unless it’s corroded or torn.

On the 1978 center dash connector you have the following wires.

Left side: Driver

Black Ground for Temp gauge.
Dark Green Ohms for temp gauge
Yellow Seat belt warning lamp power
“blank”
“blank”
Orange Clock power wire

Right Side: Passenger

Gray Lamp power wire for all dash lamps
Pink/black Hot for fuel gauge, temp gauge, amp gauge, oil pressure
Pink ohms for fuel gauge
Black Ground for fuel gauge and low fuel lamp
Brown Generator lamp ground
Tan Oil pressure gauge ohms wire.

If you go to our web site, there is a instruction sheet on removing the dash pad. This sheet also has directions on how to remove the center dash cluster. Here is the link: http://willcoxcorvette.com/repairand...lp.php?hID=263 I think the center cluster starts at the bottom of page 3.

Willcox.

 

Is this related to your LS engine swap? That's an important thing to mention.



Rick B.

 

Wow, did he do an engine swap

If so, you might want to verify the inputs on each wire on the dash cluster connection.

Willcox

 

i have swapped in the ls1. i am still using the stock fuel sending unit in the tank. i have adapted the original oil sender to the ls1 block. i have also changed the water temp sensor to a 1998 ls1 sensor that has a 3 wire connector with the third wire connected to the factory gauge. john at speartech says the temp sensor will work with the factory gauge. the oil and fuel gauge are all the way to the right. the alternator gauge works and i am not sure about the water temp yet. i started it up for the first time sat and only ran it for a minute or two. i was afraid to go longer without knowing the oil pressure.

 

That's interesting about the temp gauge and this may be what is knocking you out!

The dash unit already has power and a ground running to it! So the only thing you need from the engine sender is a ohms signal. You need to figure out which plug on the sender has the ohms reading and run this to your old temperature gauge wire. What purpose the other wires on the sender connector control I have no idea.

To make the dash unit work properly, you’ll need an input signal from the sender measured in ohms, 12 volts and ground. Same with most of the other gauges.

On the 77-78 style gauges you’ll need about the following inputs at the following temperatures.

100 degree’s on the dash unit requires around 446 ohms input.
200 degrees’ on the dash unit requires around 81 ohms input.

If you are not getting readings like this from your sender to the dash unit it will not function properly.

Make sure you are only feeding ohms on any of the senders you have installed in the engine. One input wire receiving power instead of ohms would knock out most of the console gauges. You can either probe the wires you have hooked up or you can remove the center cluster and test the wires on the connectors.

Another alternative on the temperature sender is to take your old sender and turn it down to fit the new engine. There is enough room on the sender to turn it down and then re-thread it to the needed 3/8 n.p.t.

Good luck,

Willcox Inc.

 

the temp sensor has 2 wires for the computer and one for the gauge. i took out the gauge cluster and tested the wiring harness. i received voltage on the power wires and ohms on the sensor wires for the temp and oil pressure wires. the fuel gauge wire had nothing. as i am really not sure how to test for ohms i cant tell you what the readings were. i plan to make up wiring and test each gauge individually. ill run a power, ground, and sensor wire to each gauge one at a time. i think that will help to find out if the sensors are the problem.

 

Blue:


That can be done easy, but I'm not sure how you knew you had ohms on the wires from your statement above. :dizzy: You really don't need to pull the gauges at this point. You need a multi meter to test for ohms which is a measurement of resistance created by the sending unit.

On a multi meter you set it to the 200 range. Heck, really you should go to this page, there is some detail on the 77-82 fuel gauge. Also it will show you how to test for ohms and what is needed. http://willcoxcorvette.com/repairand...lp.php?hID=277

Willcox

 

thanks for the help so far. i wasnt sure what ohms setting on the meter was correct thats why i couldnt say for sure what the reading was. i did have it set on 200. i removed the gauge cluster and wired the gauges one at a time. the oil pressure works when wired direct but none of the others worked when wired direct. the ohm reading on the temp sensor was approx 1100 at approx 70 deg which sounds too high. i get no ohms from the fuel sender so i am going to drop the tank and remove it to further check it. but when the gauge cluster is connected to the dash harness none work. i get power from the power wires and ohms from the temp and oil sender wires at the plug from the wiring. none of the connectors on the printed circuit are coming loose. is it possible there is a short somewhere in the printed circuit? can i connect the gauges to the dash harness and then check the terminals on the back of the gauges?

 

Ok, “i removed the gauge cluster and wired the gauges one at a time. the oil pressure works when wired direct but none of the others worked when wired direct”

Are you sure you are wiring the gauges correctly and have you tested the resistor on the back of the gauges? If you want to send them to me I can test them for you in about 5 minutes. . . No charge. But if you are sure you have them wired correct check them to the picture below. Then verify the grounds on the connector!

Do the gauges do not work, show any movement? What are the needles doing?



Temp Gauge Sender. 1100 at 70 is possible and is probably related to the change over. I don’t know what the sender on this type engine would put out.

Take some ohms readings on the sender while the engine is running and mark the temp with an IR gun. This will tell you if the sender is working in a close area as to what is required by the gauge.

“i get no ohms from the fuel sender so i am going to drop the tank and remove it to further check it. but when the gauge cluster is connected to the dash harness none work.”

Do not pull the tank, pull the upper boot and see if you can access the ohms wire. Then go to the gauge help and repair for the fuel gauges, there is a section there on how to test this wire. Truthfully there is enough info in this sheet to diagnosis what ever is wrong with the gauge or the sending unit. HERE

Willcox

 

when i first started the ls1 i had the alternator gauge working. it now doesnt work. i checked the printed circuit and the power connection in the circuit to the alternator is melted and the fuse for the gauges was blown. im not sure what happened. i probably damaged it one of the many times i removed and reinstalled it. so now i guess i have to replace the printed circuit before i can procede.

 

in my other post i forgot to ask if you could identify some wires in the drivers door. the wires are yellow, black, blue with a white stripe, and im think white or possibly light blue. the yellow is hot with the ignition in the on or off position. the door must have been replaced at some point because when the paint was stripped the door had a different color under the layers of paint. could this be power door lock wiring? my car isnt equipped with power locks so i am thinking the replacement door had power locks and when it was installed they just rolled up the wiring and left it in the door. thanks for taking the time to help.

 

here are some free wiring diagrams on some vetts i found on the web for free, they have been very helpfull to me.

http://www.nrjvette.com/johdotukset/?c=d;o=d
maybe this will help you track down some wires,hope it helps

 

Blue,

You can test the printed circuit with your multi meter before you replace it. If you test the continuity from point A to B, you will know if the circuit is bad. Normally if the circuit is blown, you can see it on the board.

Willcox

 

willcox,
are you still willing to test my gauges? if you are where would i send them and to who's attention? thanks.
rich

 

Yeah No problem.

Send them to:
Willcox Inc. c/o Service Dept.
123 E. Maple St.
Jeffersonville, Indiana 47130.

 

willcox,
thanks for the all your help. i work alot and cant work on the car as much as i want. anyway i decided to order a new printed circuit from you and try to fix the gauge problem my self. it arrived and i installed it and the oil pressure and water temp gauges work. the fuel gauge still didnt work so i removed the sender from the tank. as i wasnt getting an ohms reading from it i cleaned the sender and wiring and it now works. again thanks for offering your help and your tech tips on your website.
rich