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MG TD TF 1500 - Ignition Light Comes On at Higher RPM

Help needed for woman in our MG club having trouble with her restored TF. (She works on it herself.)

Condition:
The ignition light comes on when the key is turned to ignition. The light goes out after the engine starts and is rev’ed above idle.
At higher RPMs, the ignition light comes on again, getting bright as the engine is rev’ed higher. It becomes as bright as when the engine is off.
The ammeter indicates proper charging in all conditions and with the headlamps turned on. (Discharge shown with the engine off.)

Tests:
System voltage at 2000 rpm is 13.5V. climbs to 15V with higher rpm. This is with the engine still cold after hard cranking (car parked in semi-outdoors storage)
When the ignition light comes back on at higher rpms, there is no voltage from A1 to D on the regulator. Thus the light should not be on.

History:
The car ran fine and normal until a drive in August. This was with an electronic regulator not the stock 5-terminal regulator.
Since the light came on, the woman has had the generator tested and tried a new stock regulator. She was careful to polarize the system after reinstalling the generator and regulator.
The woman was careful to transfer one wire at a time between the regulator units. It appears to be wired correctly.
The battery is new. The car is wired positive ground.

I was only there long enough Saturday to confirm the conditions and make some voltage measurements. I wonder if there is an issue with the ignition light circuit itself, or the ignition switch. I took her another generator as a test.

Sugegstions?

Thanks,
Dan
D.P. Shockey

Dan - The two connections to the ignition light are 1 to terminal D on the Control box (regulator). The other connection to the ignition light goes to the ignition switch. If the light is wired correctly, then the regulator is most likely to be the culprit. Cheers - Dave
DW DuBois

Could be that the belt needs a little slack taking out, as the revs increase the belt 'bells out' and reduces the contact on the pulleys, so slips.
Ian Bowers

Ian...think you've nailed it.
Gene Gillam

If it was the belt would you not see a drop in tacho reading as belt slips?

Don't overtighten the belt, look for an article by Dave DuBois on the ideal tension.

Peter

P G Gilvarry

This thread was discussed between 11/12/2017 and 12/12/2017

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.