Testing cluster and console lamps '70

[Justin S.]

My dashes are removed from the car.

Using a logic probe I tried to inject 12v to the source of the pigtailed 20 ga. gray wires on the fuse panel and using the ground on the radio plug.

According to the schematic this ground is common to the instrument panel.

Only one lamp worked using this method. The only way I was able to test them was probing each lamp.

Can someone tell me what I did wrong?

[Mark E.]

Re: Testing cluster and console lamps '70

Are the bulbs plugged into their sockets? And is the metal portion of the dash connected to the harness ground?

[Justin S.]

Re: Testing cluster and console lamps '70

Mark,
Yes the bulbs are in their sockets. It's a spaghetti factory of wires since everything is disconnected.

Would grounding my probe to the metal portion of the dash complete these circuits?

[Mark E.]

Re: Testing cluster and console lamps '70

Mark,
Yes the bulbs are in their sockets. It's a spaghetti factory of wires since everything is disconnected.

Would grounding my probe to the metal portion of the dash complete these circuits?

If the metal portion of the dash is attached to the harness ground then it doesn't matter if the negative probe is connected to the dash or the harness ground. Check those connections carefully.

[Justin S.]

Re: Testing cluster and console lamps '70

Do you have a picture of that ground wire attached to the dash or identify on the schematic which ground to connect to?

Like I mentioned everything is disconnected and I was connected to the 14 GA. ground at the radio plug which looks like a common ground.

[Mark E.]

Re: Testing cluster and console lamps '70

I don't have a photo of the backside of the dash.

Is there continuity between the ground terminal you're connecting to and the metal instrument housing?

[Terry M.]

Re: Testing cluster and console lamps '70

I am not familiar with the kind of probe you used, but I have to wonder if the probe can produce enough current to light all the lamps.

[Justin S.]

Re: Testing cluster and console lamps '70

Terry,
I'm using an All-Sun EM285. It has an 8 amp overload protection.

Unless my understanding of overload protection is wrong I wouldn't think that any of lamps would work in that circumstance.

[Terry M.]

Re: Testing cluster and console lamps '70

Terry,
I'm using an All-Sun EM285. It has an 8 amp overload protection.

Unless my understanding of overload protection is wrong I wouldn't think that any of lamps would work in that circumstance.

That is correct. If the overload protection (whatever means is used) has activated no lamps would light. My thought was the tool may not have had enough power to light all the lamps, but at 8 amps, or slightly less, I would expect all the lamps to light. My lack of familiarity with the tool lead me to question its power capabilities; but the specifications you cite should be more than adequate for the task.

[Justin S.]

Re: Testing cluster and console lamps '70

Terry,
This circuit tester is a lifesaver when it comes to using it while the car is disassembled.

It makes the replacement of any failed device or part of the harness a breeze.

I wanted to test everything behind the instrument panel and console prior to installation to save future heartache......and backaches.

[Terry M.]

Re: Testing cluster and console lamps '70

Terry,
This circuit tester is a lifesaver when it comes to using it while the car is disassembled.

It makes the replacement of any failed device or part of the harness a breeze.

I wanted to test everything behind the instrument panel and console prior to installation to save future heartache......and backaches.

That sounds like a very useful tool. Can you share a SnapOn number?

[Justin S.]

Re: Testing cluster and console lamps '70

Terry,
A Snap-On model would be EECT-900. This would be overkill for a vintage model Corvette but great on modern varieties.

I'm using a more disposable however useful version as mentioned above.

Search for automotive logic probe and a bunch of different types pop up.