[spb350]

I'm trying to figure out why my gauges are not working. Should the blue wire for the oil sender have power? When I connect a test light to it and a ground the light goes on when the key is in the run position.

[69geeto]

That is correct. You are seeing the voltage through the gauge. When this wire is grounded (or taken closer to ground through the sender) the gauge should move.

[spb350]

So if I ground this wire and the gauge doesn't move mean the gauge is not working? The tester light is not very bright when it is attached to the blue wire by the way like its only getting limited voltage.

Does the tan wire that runs to the gas tank sending unit also have power like the oil sender wire? When testing it with the test light I have no power. Thanks

[2002Z4CSS]

Originally Posted by spb350

So if I ground this wire and the gauge doesn't move mean the gauge is not working? The tester light is not very bright when it is attached to the blue wire by the way like its only getting limited voltage.

Does the tan wire that runs to the gas tank sending unit also have power like the oil sender wire? When testing it with the test light I have no power. Thanks

The dim bulb is from the resistor on the back of the gauge. If you don't get similar power on the tan wire either there is an open from the gauge to the sender or the gauge is bad.

[69geeto]

Yes, both work the same way. The feed is from the gauge end, and the closer to ground you take the blue/tan wire, the farther the gauge will swing. You might be better off with a volt meter when measuring to get a better reading.

If you ground the blue wire, the gauge should move. Don't leave it on too long though. I think it should a few hundred ohms to ground from the sender.
Another thought is measure the resistance (with the wire disconnected) of the sending unit. If open, that's your problem.

[2002Z4CSS]

Usually a 12v test light with a real bulb will have enough resistance to make the gauge read in the middle when grounding one end and touching the gauge circuit with the ign key on.

[Peter Serio]

Most GM car dealerships, even back in the olden days would have lots of specialty tools. Back in the late 1960s/early 70s one of those was this Ser-con Tester. Basically any decent quality modern Multi-meter (at least over $100 in price) will do the same thing.

Here is the test page for the oil pressure gauge out of the booklet that came with the Ser-con tester. The regular shop manual does have the wiring diagram in it as well.


I hope this helps.

[spb350]

I think my gauge must be bad. I have power to the blue wire which means I have power to the gauge right? When I ground the blue wire the needle doesn't move a bit. I have the same thing going on with the temp sender, I grounded the green wire right off the back of the gauge and no movement. The red wire has power going into the back and the ground is good too. Really sucks I paid about $500 for the set about 4 years ago from somebody off Ebay and I'm thinking they probably knew they were bad. Does anybody know who makes these gauge sets? I really would like to just replace the bad gauges instead of the whole setup. Somebody mentioned Bruce Logan in Cali. Any help appreciated

[spb350]

Originally Posted by Peter Serio

Most GM car dealerships, even back in the olden days would have lots of specialty tools. Back in the late 1960s/early 70s one of those was this Ser-con Tester. Basically any decent quality modern Multi-meter (at least over $100 in price) will do the same thing.

Here is the test page for the oil pressure gauge out of the booklet that came with the Ser-con tester. The regular shop manual does have the wiring diagram in it as well.


I hope this helps.

Thanks

[Peter Serio]

If you can post photos (front and back) and/or PM me and I will PM you in reply with my EM address. Send me some photos of the gauges directly. One question, are these older plastic reproduction gauges or original GM parts? If they are original GM rally gauges I am sure I could fix them for you.

[spb350]

Originally Posted by Peter Serio

If you can post photos (front and back) and/or PM me and I will PM you in reply with my EM address. Send me some photos of the gauges directly. One question, are these older plastic reproduction gauges or original GM parts? If they are original GM rally gauges I am sure I could fix them for you.

The gauges are still installed in the dash but here are some pics. They are the repo gauges, bought them about 4 years ago.

[Peter Serio]

I see a big issue in your #2 photo. Whoever made these (these are homemade parts) not GM. The way the temperature gauge electromagnetic coil is "clocked" to it's dial. I can see what looks like an original ground strap coming off of the cigar lighter. The top extended tab of the ground strap is on one of the temperature gauge mounting studs. The way he built those is incorrect: that copper stud IS NOT THE GROUND STUD so right there your temperature gauge is not going to work at all!

[Dave73TA]

Fuel sendor ohms for GM are 0 - 90 ohms .

[Peter Serio]

Absolutely: Tan wire to body ground; zero or 1 ohm resistance will give you an "E" reading on the gauge face and 88-89 or 90 ohms resistance should give you "F" or full. 44 or 45 ohms should give you approximately 1/2 scale.