Need Help: 1974 Chevy Instrument Cluster Lighting Problem

[DeppvomDienst]

Hi:

 

Merry Christmas and a Happy New Year to all you fellow GM truck guys and gals.

 

I have a 1974 C-10 stepside. I am installing coolant temperature and oil pressure gauges where the idiot lights for those same two functions used to be. To do this I had to cut out a good chunk of the cylinder-shaped recesses in the plastic instrument cluster carrier where the idiot lights used to be so that I could put the gauges in there. I decided to leave the "GEN" and "BRAKE" idiot lights alone. They actually fit in well and I thought I was pretty slick doing it that way, but read on.

 

Simply put, now the speedo and heater control head will light BUT the fuel/oil press/coolant temp gauges will NOT light.

 

I had this problem when I first did the installation a couple of weeks ago. I thought this problem was caused by the absence of the two twist-in idiot light bulbs for coolant and oil on the circut board, causing an interruption in continuity. (I can't re-install them since as I said above, I cut the plastic out to make space for the gauge housings.) I tried bridging this gap on the old ciircut board with a short piece of wire but this just fried the circut board, which cost me the 100 bucks for a new one from LMC Truck. Once I got the new one, I thought that I was back in business but no such luck since I have the identical problem with the new circut board.

 

 

As an aside, I still can't figure how those bulbs have a ground since they just have two contacts that look like they are both positive, in other words, connected in series. The fuses are fine and everything else is working. I am pretty sure the bulbs are all fine but I probably should check that a third time. There very little possibility that I put potentially bad bulbs back in the exact same places, causing a duplication of the problem. Also, in order to get juice to the new gauges I sandwiched the red wires between the contact of a twist-in and the circut board. I grounded the new gauges directly to metal. One more thing I just thought of is that one of these twist-in lights is connected to a wire from the wiring harness. It must be a feed and from what I remember, I did put it back in the same hole in the circut board. On the off-chance I did not, could putting it in the wrong hole be the problem?

 

 

So again, for some reason, the instrument cluster lights on the fuel gauge side as well as my new oil pressure and coolant temp gauges will not light. I will say at this point that original to the truck there are only two big gauges, speedo on LH and fuel on RH with the rest being idiot lights (that only come on during starting) and the lights on the heater control head.

 

 

I know that it is tough to give advice without the truck right in front of ya. Sorry for the long post but I really would greatly appreciate anybody's advice on this.

Thanks,

Depp