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MG TD TF 1500 - Possible headlamp issues?

I have been having a heck of a time tracking down an electrical problem in my TD. The obvious problem is that I am not getting a charge. It is a very long story but I have decided the problem is in the 9 post regulator. Generator has been tested and a new battery installed. I have a fresh regulator installed and currently show a charge. Last year I installed the Moss PL700 headlamps (156-898) to replace the plain Jane lamps (171-100). I am wondering if anyone knows if this PL700 require more power, causing my regulator to overload? When I turn on my headlights the amp gauge dips dramatically to the negative side. The generator should kick in and keep up with the added power draw I would think? Any thoughts on this?


Rich King TD 8732

My guess would be short in one of the headlamps. Not the lamp itself, but likely the circuit.

If you can, disconnect the wiring for each separately and note change on your amp meter.
My money would be on a bad socket or weak ground.
When I re-wired my car I put independent fuses on all my lighting. It sure makes this easier.

Condition identical to what you describe was found to be caused by a bad socket in one of my wing lamps. Not a dead short, but enough to load the system.

good luck
David Sheward 55 TF1500 # 7427

Check to see that the new head lamps are not connected in series through both filaments.
If you have a high discharge and dim lights in one position and normal in the other then that's what happened.
Had it happen when changing to a seal beam unit with built in sidelight.
Ray TF 2884
Ray Lee

You don't mention at what speed (RPM) the ammeter dips negative. Generators have almost no output at idle and I would hazard a guess that if you're under 3000 rpm, you will be negative in the charge department. This is the main reason people go through the effort of converting to alternators.

L Vince is correct. PL700 will really pull down the power and below 3.000 rpm you are probably loosing charge, especially with high beams.

But none of this hurts the regulator, that is what it was designed for. And the battery plays a role here too, providing adequate power when the rpm temporarily drops below the charging level.

As long as you are charging or at neutral you are fine. If its constantly discharging then you have problem with your generator or VR or both.
Christopher Couper

Rich, the bulb in the PL700 is rated at 40 watts on low beam and 60 watts on high. The plain Jane 171-100 is probably a standard sealed beam rated at 35 watts on low and 35 watts on high. A tungsten halogen sealed beam is probably 35/50.
2 of the PL700 lamps on high would then draw about 120W/12V ~ 10 amps total. Your Plain Janes would draw 2*35=70W/12V ~ 6 amps total. Would I expect the extra 4 amps to raise Cain with your generator/regulator? Not likely. When you turn the PL700s on they should show a discharge on your ammeter of about 6 amps on low and about 10 amps on high. What sort of numbers do you see? Check with the engine not running. Bud
Bud Krueger

This thread was discussed on 29/06/2014

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