Okay so some backstory. I put in the 120A bnr alternator and four months later the magnet coil burned out. Open circuit on the slip rings. In he meantime I’ve reinstalled my bosch unit that had the glowing charge light that would only go out if you blip the throttle.

Basically I rebuilt my system to what it was before and I got the old problem back. Start up and the light is on. Blip the throttle and the light turns off. Before the blip, no charging, after the blip charging.

Very odd and frustrating.

So I figured it was time to start digging. I did the following and non of it worked.

1) cleaned the connection at the alternator blue wire at alternator. Still needed a blip to cancel the charge light.
2) cleaned the blue wire at the screw bulkhead on the passenger side fender. Still needed the blip.
3) cleaned the two prong connector on the blue line up by the washer reservoir. It was really corroded but it still needed the blip. It was better now in that once warm a restart wouldn’t require a blip to turn off the battery light. But it still needed a blip on cold starts.
4) changed to a new 3W bulb on the charge light. Still needed he blip.

So I read on the pelican porsche groups guys were putting a 91 ohm 5W resistor in parallel with the lamp to get their cars to boot the alternators without a blip. I worked the numbers and that equated to about a 7W light bulb equivalent. Putting in a resistor sounded too hard.

So I went to Walmart at found Sylvania 2835 5W bulbs in the same form factor as our charge lights. I put it in. Now no blip required at startup.

Hooray!!! But now I own an extra 120A BNR alternator. Wasted my dough. A higher wattage bulb solved it.

Is it possible the OE lamp is 5W?

Anyone got a parts manual?

There are also some power resistors on the board next to the lamp. Maybe they are a 91 ohm load in parallel with the lamp and they’ve gotten old? Solder joints cracked and overheated after 39 years of starts? I didn’t have the patience to tear down my cluster and look at them closely. I just saw them in photos of disassembled instrument clusters online. There are some big resistors mounted around that lamp by design.

It seems like a silly design decision to use a lamp as a resistor. The resistance changes with filament temperature. This was a very old Hewlett-Packard trick from the 50s on their first signal generators. It is not good design. Modern halogen peanut lamps may be more efficient and a 3W today may not draw as much current at a 3W in 1982. Just a wild thought.

Hopes this helps you guys with glowing lamps at startup that need a throttle blip.

Try a 5W battery charge light bulb!

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79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles