1986 720 Gauges not working

[captain720]

My 720 is having a few weird electrical issues, none of the gauges work, and the left bumper mounted turn signal is sporadic. The oil pressure sensor, fuel gauge, alternator amperage gauge, and the hand brake light doesn't work (not sure about speedometer and temp gauge as I have not driven it around since these issues developed). Thursday night I unplugged the turn signals and pulled my bumper out (it had been dented in, it is aftermarket), then I applied dielectric grease to the bumper mounted turn signal connections and plugged them back in and the both worked. Then I physically mounted a pair of fog lights and have not wired them yet except for adding a wiretap to the fuse block and unplugging the old switch (which I plugged back in again). Then I fired it up to go somewhere and the battery light came on and none of the gauges worked. My battery is giving 12.5 volts without the truck running and 13.8 at idle varying directly with engine rpm and load. Is there a fuse-able link or a fuse that powers all of the gauges? Or a wiring harness or ground that would come loose?

If there is a thread with this already please point me in that direction. I am a new member and the 720 is my first vehicle so no detail is too small and no knowledge to common.

[datzenmike]

Which fuse did you tap into? I would start there.

[captain720]

I put a wire tap on the heater/AC fuse, AC still works but maybe I broke something putting it in? Are the fuse blocks delicate? I will be wrenching on it today quite a bit as I have some break pads and other stuff to take care of.

[captain720]

I just went and monkeyed around a bit and all the fuses have good voltage, so I fired it up and all the lights and gauges work. It is super wet down there because the front window gasket is shot and rain is pouring in onto the fuse block.

[captain720]

Also I am not able to locate a thread on the proper voltage for a coil, I am only getting about 10.5 volts. I also have my choke drawing power from the coil, although the voltage is the same there before and after wiring the choke up to it.

[datzenmike]

 Check your battery voltage. Should be 12.6 engine off and 14.3 or maybe a little higher with it running.

 

The intake coil gets it's power directly from the ignition switch so should read the same as the battery. The exhaust coil is from the ignition but runs through the #1 fuse in the box.

 

 

You should be getting your choke power from the choke heater relay but if it's not working, connect it (the Blue wire) to the Red idle cut solenoid wire right beside it.

[captain720]

When it idles without the heat or lights or radio or anything it gives 13.8 volts at the battery unless I rev it then it will get up near 14 is that acceptable? I don't need a new alternator do I? Also what ground should I check for my headlights/brake lights? The brake lights are sometimes sketchy and the headlights are very dim. The entire trucks wiring is very sketchy.

Thanks

[captain720]

The gauge issue was being caused by the rain pouring in, I put some silicone on the gasket and I will be getting it replaced soon.

[datzenmike]

Headlights work like this....

 

Battery

fusible link

fuse box

light switch... sends power to

head lamps

headlamp relay... selects HI or LOW beams

grounds HI or LOW to turn them on .

 

 

 

When it idles without the heat or lights or radio or anything it gives 13.8 volts at the battery unless I rev it then it will get up near 14 is that acceptable? I don't need a new alternator do I? Also what ground should I check for my headlights/brake lights? The brake lights are sometimes sketchy and the headlights are very dim. The entire trucks wiring is very sketchy.

Thanks

 

Sounds like low output from your alternator. Is it a rebuild with a sticker on it. They are poor quality.