Headlights dim/bright

[bamarover]

Our headlights on 1971 IIA are dimmer at idle and brighten up when rolling - not a huge amount, but enough to be noticeable. What causes this and would relays fix it ?(our headlights are GE halogen form one of the LR vendors). If so, what relay should we use and tips on where in the line to install. If not, could it be an alternator/slow idle issue (550 rpms)?
Thanks,
Greg

[Geobloke]

Originally Posted by bamarover

Our headlights on 1971 IIA are dimmer at idle and brighten up when rolling - not a huge amount, but enough to be noticeable. What causes this and would relays fix it ?(our headlights are GE halogen form one of the LR vendors). If so, what relay should we use and tips on where in the line to install. If not, could it be an alternator/slow idle issue (550 rpms)?
Thanks,
Greg

Hi Greg that is perfectly normal. It is caused by the increase in charge being generated by your alternator/dynamo (depending on what you have fitted).

If you want you can adjust the idle a bit (speed it up), but in all honesty i'd leave it as it is.

Check that your belt is properly adjusted too, should be about 10mm play in the belt either way (up and down).

[pickuprover]

Relays are always a good idea especially when running hologens (now that being said, I still have not gotten my relays installed.) The wiring on these old truck is yes old, and also when new, they were almost at max capacity. The relays are easy to instal.... Use the existing wires to power the relay, run new wires from a power block to the relay, and then from relay to the headlights. Then when you flip the switch, the old wire is carrying only the amount of power needed to turn on the relay, and the new heavier wire is carrying the power for the headlights.

As for the dimming, I am trying to remember an old rover that did not brighten up when running at speed. I tend to have my idle set higher as I drive in stop and go traffic, and it is easier to feather the clutch at higher idle ( I can almost take off from a standstill on a bit of an incline without touching the gas.... )

[300bhp/ton]

yep perfectly normal for almost any car that's 30 years old+ in design.

Bigger alternator and/or battery may help out. Bet if you put your indicator on while idling with the lights on the relay is really slow, up the revs a bit and lights will brighen and the indicator flasher speeds up.

[bamarover]

Okay, as long as normal and not indicating some problem we decided to leave as is for now. We are adding some driving lights soon that have relays, so we will see how they hook up and may add them later as pickuprover suggests.
Thanks!