Electrical system question

[apache]

Watching the factory dash volt gauge on my recently aquired 85 Suburban has me thinking there is a intermitten short somewhere. Driving on my 40 mile commute the volt gauge would go from a normal above 13V reading down into what looked like discharge territory. It would gently sweep back and forth staying at the low mark for 15 seconds or so then back up over 13V again. Never had starting issues or otherwise mind you.
So today I ran a lead off the firewall 12V terminal block by the master cyl to my DVM placed on my dash. Driving 40 miles home the DMV started at 14.7 V and near the end of my drive 13.4V,never taking a dip lower. The gauge bounced around like always. My question is this, regardless of where I tied the DVM to,battery etc, if the system was actually dropping down like the gauge showed the DVM should follow shouldent it??

 

[dremu]

Sounds like the gauge or the wiring to it is flaky. Yes, the second meter would pick up system-wide fluctuations.

Also sounds like you have a charge problem or something, 'cuz after a 40 mile drive the voltage should be up, not down. Unless you were driving with a lot of lights on and at slow speed.

-- A

 

[BIOHZDK5]

Try measuring the output on the alt. Should be the same but it sound like the gauge is on the brink. Might be slightly more difficult but could try the DVM reading at the gauge. If you are going to crack open the dash bezel to possibly replace the gauge might as well trouble shoot it first before tearing the cluster apart. Just a suggestion! Or could be them pesky gremlins!

 

[Thunder]

Also sounds like you have a charge problem or something, 'cuz after a 40 mile drive the voltage should be up, not down. Unless you were driving with a lot of lights on and at slow speed.

-- A

Going from 14.7 V to 13.4 V after a 40 mile drive sounds good to me.
In a healty electrical system the voltage regulator will drop the voltage as the battery charges, to avoid overcharging the battery. As long as you dont go below 12.5 volts things are usually fine.