• 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Dimming dash lights
#1
Hello,

Have a 73 convertible 351c, no AC. Notice that at idle dash lights dim a little if I rev the engine or accelerate they brighten. Otherwise the charging system seems to be fine. Cranks rapidly, always starts ... no issues. The alternator appears to be a fairly new aftermarket replacement. The battery really dont know much about. Is this normal or an indication of a problem ? Thanks
  Reply
#2
Normal. At idle, the alternator is supplying the battery with power, but not a whole lot. By the time the little electrons reach the dash lamps, many have been trapped at various connectors and converted to heat (voltage drop). Revving the engine brings maximum charge to the battery (14.6V or so) and thus a few more electrons make it to the lamps. Typical voltage at idle around the dash area is 10.5V, when not at idle, it may reach 12.0V.
  Reply
#3
midlife;199049 Wrote:Normal. At idle, the alternator is supplying the battery with power, but not a whole lot. By the time the little electrons reach the dash lamps, many have been trapped at various connectors and converted to heat (voltage drop). Revving the engine brings maximum charge to the battery (14.6V or so) and thus a few more electrons make it to the lamps. Typical voltage at idle around the dash area is 10.5V, when not at idle, it may reach 12.0V.

thanks very much
  Reply
#4
Do LED bulbs in the dash cluster exhibit the same dimming, or, do they maintain brightness? Just curious if they respond the same way as incandescent bulbs.

Pics of The Car
  Reply
#5
I have not noticed this effect in my LEDs.

<img src="http://www.7173mustangs.com/gallery/1_12_09_14_10_32_45.png" />

- Nik
  Reply
#6
Very normal. If you upgrade your alternator to a beefy 100A then you definitely won't see this. Most provide 65-75A at idle. Stock alternators are 35A I think. Other possible issues with crazy lights are the VR and 5V CVR in the gauge cluster.

Non-dimmable LEDs shouldn't exhibit any fluctuation is light since they are on/off. I doubt dimmable LEDs would be effected either.

KR

-Former 70 & 72 Mustang Owner.
-69 Torino GT, Formal Roof, 351W, Edelbrock 600 cfm, Edelbrock 351W Performer RPM intake, headers, AOD trans, dual flowmasters w/H pipe, Pertronix II Billet, 3.5 TRACLOC g/r, 15" Magnum 500s, 100A alt, aluminum radiator, electric fan, Pro-car seats, mini-starter...owned since Dec 13.
-70 Mach 1, 351W, Edelbrock E-Street EFI, VHX instrument cluster, Hooker headers, dual flowmasters, Pertronix II, 15" Magnum 500s, 150A alt, aluminum radiator, dual electric fans, Pro-car seats, mini-starter
  Reply
#7
I have stock 351c, alternator, regulator and at idle no dimming lights. At start up voltage reads 13+ tapped from
positive radio wire.

Seems I remember a loose alternator belt would cause that issue.
  Reply
#8
Hello Folks! I am new here and have been going thru the topics to see which ones apply to me. I found this one as my dash lights are extremely dim and they stay like that regardless whether is idling or not.
I have read some of your answers and did not find one that applies to me. My alternator, battery and belts are working properly.
Any suggestions?
Thanks,
Siggy
Ps. 72 Mach 1
  Reply
#9
Yeah. Don't drive at night.

Seriously, these bulbs were dim way back when. Several folks have upgraded to LEDs with good success.
  Reply
#10
+1 Midlife

Dim dash lights are the norm for whatever reason.

LED bulbs are an option but they are "ON" or "OFF" no adjusting brightness.

I don't drive my car at night much and live with it... however I have aftermarket
gauges for Oil Pressure, temp, and volts that are well lit.
  Reply
Share Thread:  


Possibly Related Threads...
Thread Author Replies Views Last Post
  Fix For Dim 71 to 73 Mustang Dash/Instrument Panel Lights OLE PONY 32 25,457 07-17-2018, 09:25 AM
Last Post: midlife
  Dash lights working!!! scgamecock 1 228 03-12-2018, 06:50 AM
Last Post: midlife
  Tips for troubleshooting dash lights? scgamecock 7 403 02-04-2018, 12:36 PM
Last Post: midlife
  Still no dash lights!!!! scgamecock 3 299 01-16-2018, 06:36 PM
Last Post: nailpounder
  Column have to be in for dash power to work? scgamecock 4 593 12-30-2017, 05:24 PM
Last Post: midlife
  Head Lights goodnigh 24 1,526 12-11-2017, 10:04 PM
Last Post: goodnigh
  New dash panel install Omie01 1 326 12-08-2017, 09:09 AM
Last Post: SVO2SCJ
Wrench Dash lights voltage regulator John J 3 528 09-29-2017, 05:25 AM
Last Post: midlife



Users browsing this thread: 1 Guest(s)