I have a 2002 F150 with 82K miles and I have noticed the dash lights are surging (dimming for a second and going back to normal). It just started a week ago and does it at idle or driving down the road. The truck seems to crank like normal and the battery is a 4-year old yellow top Optima. Any suggestions will be appreciated. Thanks.

 

I would say ( due to it happening when the truck is standing still ) that the dimmer switch has some dust built up in it.

You can cycle the dimmer switch up and down a few times, and blow it out to see if this does the trick.

If not, the next step is to temp bypass the dimmer switch, to see if the problem persists.

I would start with giving the switch a good blow out ( don't forget to have the line dryer if you use the compressor in the garage ) and cycle it a few times.

 

I will try the dimmer switch tonight, but it does the surging driving down the road OR at idle. I looked in my records and the Optima is 5.5 years old. We are going to swap in a different battery tonight and see if it helps...could the battery cause this? Thanks.

 

I would definitely get that battery replaced, it might be on it's last legs. Also might want to get the alternator checked out (tested). That symptom is classic of a voltage regulator going bad.

 

Thanks for the help...rolled the dimmer a few times and the problem appears to have vanished. I swear my dash lights are dimmer than they have been...my Edge box show 14.2V driving/14.1V at idle/12.2V with engine shut off. Any ideas? Thanks.

 

Too much dust/ other in the rheostat. If it is bother you that much, you can try pulling the switch and blowing it out from the back or replace the switch.
The other option if you never plan on using the dim setting it sot jumper the switch on the back, bypassing the dimmer all together. The jumper would be installed on the wires, and the only function it would serve is all the way up to turn on the interior lamps.

If the instrument illumination is the only thing dim, it is not the battery, you would also notice dim headlamp ( 1 headlamp draw much more power than all the instrument illumination together ).

The at rest voltage looks low, depends on when you took it ( after how much driving, and had the battery saver relay tripped ).

If you can pull the battery, trickle charge it and once you remove the charger, check the at rest and then again in 1 hour intervals checking the at rest voltage to see if it drops.

If you have a place you trust, go right for a load test.

Could be the battery needs to be replaced, but the indicator is not the instrument illumination.