Red light intermittent - 73 Super

[Brock36]

I have an intermittent red alternator light and seatbelt light coming on at higher rpm's. Car starts fine, idles with no lights on but when driving the two lights come on together and go off and on. I am getting a voltage reading of 12.5 with ignition off, up to 17 volts with red light off, reducing to 13.5 when light turns on.
Where should I be looking for a solution?

[Marc]

Are you sure it's not the brake system warning light that's coming on along with the alternator warning light in the speedo? Those share a common input from the alternator's D+ terminal (or if equipped with a generator, regulator terminal 61).

The warning lamps in the speedo, gas gauge, brake and seatbelt warning lamps, and turnsignals all receive power from fuse #12, and the alternator receives its field flash current through the filament of its warning lamp...could be worth checking that the connections on fuse #12 are tight and clean.

[Brock36]

On closer checking it appears that I have a generator. Engine AK036647, Serial 1332365138.
It is the seat belt light. I don't have a brake warning light that I am aware of. The lights come on always together and whether the seat belts are done up or not.
Cleaned fuse 12 and contacts with no change.
Car idles forever with no lights showing and voltage at battery 14.5. At higher RPM red lights come and go with voltage dropping to 13.5 when the lights are on.
Is there something more that I can check?

[Marc]

With a generator the first thing to check is the condition of the brushes. Once they're worn down to where they're flush with the top of their holder, the spring tension's not enough to ensure good contact with the commutator. Carefully press down on the top brush with the engine idling. It should feel smooth, if the brush is moving up and down the commutator is either out-of-round or it's shucking one or more bars - either way it needs to be replaced/rebuilt - or it's a good time to convert to alternator.
If the commutator is round it's worth putting in new brushes...there are some tips that'll make that job easier, ask if you'll be going there. Bosch P/N for a pair of Type I brushes = 11 004

[Brock36]

Looking closer, it is the brake light that is coming on with the generator light. Also the brushes are badly worn and are well below their holder so I will get some new ones and replace them. The commutator looks ok but shiny where the brushes contact. You suggested some tips for replacing brushes. I would like them.
My generator has no cover for bottom access port. Should there be one?

[aussiebug]

Replacing the brushes is easy enough, just pull the flat spring clear and remove the old brushes - you’ll need to remove one screw holding the pigtail wire in place. Fiddly job, but not technically difficult.

The slots over the brushes SHOULD be left open, the main cooling fan pulls in air through those slots and into the fan housing for keeping the generator cool.

[Marc]

...You suggested some tips for replacing brushes. I would like them...

To slip the old brush out and put the new one in you'll need to pull the spring back out of the way. Do NOT pull it to the side as that can make it come off and it's challenging to put back on. I use a little hook made out of a piece of welding rod (wire coathanger works too).

Generator Brush Hook.png

The small screws which hold the brush pigtail on can be tricky to get started (especially the bottom one since you don't have a clear view of it - some folks do well using a mirror but personally I'm better off going by Braille). I have a little screw-holding driver I use for the job, but you can do nearly as well with a small strip of masking tape. Poke a hole in it and insert the screw through it from the sticky side, engage a screwdriver in the slot and pull the ends of the tape up and stick them to the shaft. Once the screw is started, but before running it in all the way, rip the tape out.



Poke some rags in under the work area so if you drop a screw it won't bounce away where you'll never find it again.

Very rarely the screw(s) will be so tight that when you try to crack them loose the tab that they thread into will bend. It may be necessary to hold the tab with some needlenose pliers.

About the worst thing that can happen is having the lower spring pop off. Easier IMO to get it back on if you rotate the whole generator around so you can see what you're doing. Some folks will even do that just to change the lower brush but that shouldn't be necessary. Requires loosening the strap, disconnecting the wires, and removing all four of the 10mm-head bolts holding the sheetmetal to the shroud.

[sideshow]

My observation is that in this country the generators nearly all had a dust cover over the upper brush and the lower hole was left open. I assume this was for both debris falling into it and to allow air flow through.

That screw holding tool looks great, but I have only seen really long ones and not all can hold the head well...so I use tape.

[Brock36]

Thanks guys. I'll be away for two months but let you know how I make out.