Current situation is gauge fuse keeps blowing causing gauges not to work. All lights still continue to function as normal. Started while driving and hit a bump with park lights on. Gauges quit working and door chime was sounding as if the key was off with lights on. Power to ground short.
I have taken a bulb and soldered spade fittings on the end and inserted into fuse location. I have tried doing wiggle test first. Behind the distributor I found my light would glow brighter and chime module would sound. I then unplugged 3 distributor connections, with this unplugged and doing wiggle test, my light would stay the same and no chime. However light was still on. Next I unplugged the oil pressure switch, both connections. While unplugging these I observed the light and noticed it would fade slightly. Wiggle test would result in no change. I then unplugged just about everything under the hood one at a time with no change. Moved to interior wiggle test no change, distributor and oil pressure sensor are still unplugged. Unplugged cruise switch no change. However when I remove the gauge cluster my light finally goes out. I then inspected the clusters printed circuit. I can not see any obvious breaks anywhere. I removed the front cover searching for lose gauges or corrosion. Everything appears fine. Reinstall gauges and light comes back on. I then checked the c1 and c2 connectors for continuity to ground.
In the c2 connector: blk/w, ltblu, dkblu, and blk.
In the c1 connector: 2 blk and ltgr.
First question since the lights all function, is it normal for the blinker and illumination wires to be grounded?
Second question are the gauges to blame?
Any insight or suggestions would be greatly appreciated along with wire diagrams. I am currently waiting on a service manual to arrive next week.
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Removed gauge cover then removed oil pressure/volt gauges from cluster then reinstalled. The test light was still on. Replaced oil/volt gauges then removed fuel/temp gauge, reinstalled cluster and my test light went off. So the problem is isolated to either my fuel gauge or temp gauge. Can I ohm these out to see if the gauge is the problem? If so what would it read?

 

Expect several tens to a few hundreds of ohms.

The resistance would have to be about 2.5 ohms or lower to blow a 5A fuse. (Ohm's Law... resistance = voltage ÷ current)

 

Well after picking at it all day. The only way the test light will completely go out was with both sets of gauges and SES light bulb and seat belt light bulb removed. Just for SG I decided to return everything and throw a fuse in to see if it blows. Fuse did not blow and gauges are functioning. What the heck? It will still light up my test light.

 

Reinstalled 10 amp fuse, turned ignition on and fuse didnt blow. Took the car out driving on my normal roads for a hour and it didn't blow. Im sure it will come back after whatever wires I moved get back to where they shorted. I tried to inspect closely the wires behind the distributor with no luck. I removed the loom from the passenger side fender ECM connection all the way across to the firewall connector and a portion of the fuel injector harnesses. No bare or broken wires were found.

 

You haven't mentioned what year your car is, but I know the later cars used the gauges fuse to run some of the emissions equipment under the hood too.

 

Excellent point. Working on a 1985 305 tpi car. Bone stock except for audio system.