Tach Dash Lighting Problem

[rsavage]

I put on new bezel and painted up the needles on the recent tach dash I picked up. Put the speedo from my regular dash in it and put the "new" tach dash in the 70 4X4. Ran a separate ground from the tach. Tack and all gauges worked well. However, I only have a single dash light on the right side-no others will light up. Only the left turn signal will light up when activated, not the right. Changed out the bulbs. No difference. Put my other new refurbished tach dash that I am going to use in the Blazer and it did the same thing. Put the original dash in and had all the lights. Anyone have any ideas?
*Note: the old dash was a dash with gauges and I checked the plug and it is wired correctly for a cluster with gauges.

[VA72C10]

Does it have a new printed circuit? Or used? Sounds like an issue in the printed circuit if the original is working...but weird both of them are acting the same.....are you using the same bulb holders in both when you test? Maybe one contact needs cleaned up?

[rsavage]

One original tach dash printed circuit on the one I was installing on the truck, and one new on the one I got from you for the Blazer. Both did the same thing, yet the gauges only panel that was in it doesn't when put back in. Right now I am stumped.

[81ShrtBox]

I would wire up some after market led bulbs and forget about it.

[Andy4639]

Where the connection is on the back side make sure the little tabs are all in line and meeting the bulk head connections. I had to play with mine before to get everything working. Also the little twist lock connectors for the bulbs can be bad are not making contact.

[bmfm64]

Are you using the same bulbs and bulb holders on all three panels?

[rsavage]

Okay. After checking and cleaning all grounds, changing bulbs, bulb holders, triple checking the plug wiring and trying both tach dashes and getting the same results, I pulled the dash gauge panel out of my suburban thinking maybe there is some wiring problem in my 70 4X4 even though it was a new harness when I restored it. Tried both tach dashes in the suburban and got the same thing. 1 Panel light on the right side and one left turn signal.
Could I possibly have two bad printed circuit boards? One was an original one and the other a brand new never used aftermarket. NO sparks, no burned spots, and they both look okay. Any further ideas? Bottom line is both these tach dashes act the same in two different trucks.

[VetteVet]

There's a gray wire from the fuse panel that feeds the dash lights and the heater switch faceplate. GM made two styles of clusters for our trucks, the seven gauge, and the three gauge with the idiot lights. Assuming that you have the seven gauge the gray wire connects to pin 8 on the cluster plug. It connects to pin 12 on the idiot light plug.
The fact that your original cluster lights work tells me that there is no problem with the gray wiring or the power feed to it from the headlight switch.

I would check the other clusters outside the truck with a lead from the positive terminal on the battery to either pin 8 or pin 12 depending on which dash cluster you have. Then ground the cluster with another wire from the battery negative.

From what you've done so far it seems to me that you have two clusters that have something wrong with them. Below is a diagram of the seven gauge cluster showing the wiring circuits. The wiring key is on the left side.The gray line to the lights is power and the orange lines is ground. By connect power to the grays and ground to the orange your lights should come on if the circuit board is OK. You could use an ohmmeter as well and test for continuity.



Here's the back of the cluster, the red wire is a power takeoff for the tach and it's off the pink wire to the fuel gauge.

[Andy4639]

Here is the back of a factory tach dash with factory correct wiring for the speed warning also.
If you look there is a screw right under the speedO on the right in the picture. I always ran a ground wire off of it when it's in the truck.

[rsavage]

I was going off the wire diagram found at GMC Paul's site
http://www.gmcpauls.com/Tech%20Tips1.htm

[rsavage]

That diagram showed the #8 spot to be the gray wire (cluster feed and heater control lamp) actually there are two gray wires to this single terminal, and the #7 terminal is shown as the ground. I did disconnect the gray terminal from the fuse box cluster feed spade and I still have power at the plug terminal. Even though your colors are different than on my trucks, the circuits for power and ground appear the same.

[Andy4639]

This is what my 71 has. As I just did a complete cluster change out. That factory cluster in my above picture is now boxed up and being saved for a later date and time if I ever want to go back with it.

[slikside]

subscribed.

[rsavage]

Andy that is what I was using but I didn't have to add the wires at 1 and 12 as my clusters were already gauge clusters.

[rsavage]

Andy - yes I ran a separate ground from the grd terminal on the tach to the cab.

[Andy4639]

Take the the dash and put a hot and a ground to a battery and play around with the bulb holders while you have it wired. I have found that some models have a differant bulb holder and they want work. I have also just played with the bulb holders and got them to come on.

[VA72C10]

The fact that both do the same thing in the suburban is especially weird....
With that info I can only assume the bulb holders to be the culprit now...One not making a good contact and continuing on the power to the rest of the bulbs....but it's still weird they both act the same...
...possibly try switching the ones from the one working correctly to one of the tach dashes and see what you get.