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MG TD TF 1500 - Headlights Dim at Idle

Hi, I have hardly ever driven my 51 TD at night, did so the other day and noticed the headlights are pretty dim at idle and then brighten up with increased RPM, doesn't matter if I'm sitting and giving her gas or driving. Not too worried since they seem to be doing their job when driving but concerned it's a reason for a ticket if I'm sitting at a red light, and of course I'd prefer they work normally all the time. Can you give me the checklist of where to start and continue troubleshooting to see if I can fix the problem.

Different topic - my running lights work fine, but are the two small bumper lights (the ones with the little red glass insert) supposed to stay on when I turn on the headlights? They don't so was curious.

Thx,

Steve
SD Denham

Start by checking the voltage at the headlights. Then look for a bad ground. Followed by a check of the output voltage at the regulator. If low at the regulator, clean its points and possibly readjust the output voltage.
Lew Palmer

Measure the VOLTAGE at the head lamps at idle.
If its less than 12V you have could excessive voltage drop in the switch/wiring.
If so then perhaps a Relay conversion would help.

If its 12V or higher, conversion to LED lamps would improve the situation.

However if you find the illumination level to be sufficient while driving, I would be temped to just leave as it is.


Jim B.
JA Benjamin

Steve

Head lights on, measure terminal voltage on your battery. Headlights on, engine running at 2500rpm measure terminal voltage on your battery.

This will give you some facts to work with regarding poor wiring terminations, regulator efficiency and batteries ability to sustain a load.

Vehicles not fitted with an earth strap directly to the engine block always seem to struggle with grounding issues as advised by an old timer this is the best modification to improve electrics efficiency.

Graeme
G Evans

Steve - Since everyone else has given you suggestions on the dimming headlights, I'll answer your other question. The answer is, yes, the side lights should be on even with the headlights are on. Cheers - Dave
DW DuBois

How old is your battery? It has to provide the voltage and amps for the car at idle, so if your lights are REALLY dim, that can be indicative of a tired, old battery.

I have a voltmeter permanently installed in the cluster and the voltage with lights on can drop to 10 Volts or even less. The new alternator still drops that low at idle, also, so that wouldn't change your headlight situation.

What's your idle speed? I usually go with around 750 rpm. If you seldom drive at night, how about picking the rpm up to around 900 just for night drives? I frequently tweak idle up and down, like it may need opening up on really cold, rainy nights when wipers, lights and heater are all on.

I also installed very bright HID headlight bulbs that only draw 3 amps each, and have been very pleased with LED headlights, too.
JIM N

This thread was discussed between 07/08/2017 and 08/08/2017

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