Dim Head Lights At Idle

[Straight Six]

Hello All,

I've got a 1970 Vitesse convertible. I've had it for 15 years now and have had no problems with the standard dynamo. Just lately however, when the engine is at idle with the head lights on the radio stops working and the indicators will barely work, especially if I put my foot on the brake. I assume this is happening because of a drop in voltage.

I have cleaned up the earth terminal where the negative cable from the battery bolts to the bulkhead and this did help the situation a bit, have swapped the battery for a known good one, checked the voltage regulator settings as per the manual and in a last ditch attempt to alleviate the problem have brought the idle speed up. The dynamo has had new brushes and the contacts inside the dynamo (I think its called the comutator?) cleaned up. However, the problem is still there.

I really don't want to change to an alternator set up as the dynamo has been perfectly sufficient for most of the car's 36 years, and one of the reasons I own old vehicles is because I like to have things a bit different to the modern stuff. It’s also annoying having to have the idle set at 1000 rpm+ after spending money and time getting the engine set up just right to allow a smooth idle at 700/750 rpm.

Any suggestions as to the possible cause would be appreciated.

Thanks

[Deleted User]

The regulator boxes are notorious for these sorts of problems, I have worked with a friends Jaguar, which we went through three until we found one that worked. And they are horrible to set up!
Bear in mind, an alternator was introduced on 6cyl small chassis Triumphs in 1968 (GT6 mk2) and you can still buy it, a Lucas ACR, so it would be a period mod!

[heraldcoupe]

Have you tested the dynamo output as per the manual? Make sure that all electrical contacts in the area of the charging circuitry are in good order. If the regulator box has been adjusted then it looks like the unit itself may be at fault. Failure of the regulator box is actually quite rare, most are discarded unnecessarily when adjustment is all that's necessary.
Cheers,
Bill.

[Deleted User]

Bill has such a wonderfully polite way of putting you down  :'(

[Straight Six]

Thank you very much for your swift replies. I have checked the voltage output of the dynamo and it was just in tolerance.

Will also check the connections on the charging side. Do I have to check other electrical connections such as those on the solenoid? I was wondering if high resistance here would affect the amount of voltage reaching various components.

Another question (sorry!) Can you still get hold of the proper adjustment tool for the control box? At present I am using the blade of a flat screw driver, but it is less than satisfactory.

[JohnD]

SS,
Have you checked the earth cable for the Engine?
Some were truely manky bits of thin braid, quite apart from the corrosion at each end.
JOhn

[Straight Six]

I haven't as yet John, but I will now! Last time I recall seeing it, it was all covered in oil/grunge.
Thanks

[gilesdive]

I might be makin a fool of myself here (nothing new) but this might be relevant.

My car has an alternator, and the problem I had (similar symptoms to yours) was caused by the earthing of the alternator - i.e. where the alternator bolts onto the engine, I was losing over 1 volt there. Don't know if dynamos have a separate earth wire or not. Easy to fix if it is the case though - undo mounting bolts, clean everything up with emery/wire brush, bolt it back on.
Even if it doesn't work, it certainly won't hurt.