I have an Autometer Air/Fuel ratio gauge and I have noticed that it is affected when the blinker is turned on moving the reading back and forth along with the blinker. It also reads leaner when the electric fans kick on and when the headlights are on and lots leaner when both are on. And as long as I have had my car, the volt gauge moves with the blinker flashing (that normal?). Atleast with the a/f ratio gauge, is that a ground problem maybe? The gauge gets power from the fuse box along with my fan relay. And it shares a ground with a whole mess of other stuff under the dash. Any ideas? Makes it hard to tune the carb when my fuel ratio changes on me when my fans come on and stuff.

Thanks!

 

It is pretty normal for the voltage to vary when accessories are on. if you pull power from the fuse panel on a circuit with a heavy load there will be more drop. Remember there IS resistance in the vehicle wiring. You might want to pull power with a tap directly from the battery, that is the point of least potential for voltage drop. Remember to use an inline fuse to protect the device you are feeding and place it as close to the battery as possible. Periodic cleaning of battery cables at batt, and where they connect to the starter and engine block helps to eliminate voltage drops.

 

I had a similar problem where all the intruments went low when the lights were on. It was caused by a broken copper strip on the instrument pod backing. when the lights came on, they tried to earth through the intstruments.

Check the resistance to earth from the blinker panel light, also work the blinkers and see if you measure any positive volts at the earth side of the bulb, in addition to testing the supply volts.

 

i have an 87 trans am and the same problem....mostly while running a/c.... i thought it was prob a ground or open problem somewhere....found a few...still does it....not as much with lights as with a/c....suspect blower motor and/or a/c compressor...

 

I don't know if the 87 has a serpentine belt, but if the lights dim when the A/C cuts in, it could be a slack belt. Just a thought.