Page 1 of 1

1975 860GT LED retrofit

Posted: Thu Feb 13, 2020 12:18 pm
by rjk40
Given the somewhat anemic output of the 860GT alternator, I have embarked on a new episode of self-torture, in retrofitting LEDs into the bike to alleviate the stress on the alternator.
I had installed the LED dash light kit that Steve and others offered, and all went well with one exception: the turn signal indicator only worked for the right hand side. As a EE, I should have remembered that LEDs are diodes, and thus are polarity-sensitive, whereas incandescent filaments are not, and in fact the turn signal indicator current will be of opposite polarities on the left or right signal switch. I then relocated both "hot" leads to the anode of the LED, with either signal switch isolated with a pair of diodes. Then, all worked fine. As luck would have it, some vendor (can't remember who) offered a unit that does exactly what I had done the hard way.

Next, the turn signal and taillight/brake light lamps.

Following is a comparison of the current draw of the original 1156 and 1157 lamps, with the retrofit LEDs I purchased from SuperBright LEDs:

1156 incandescent bulb: 1.76 Amps
1156 LED lamp : 0.18 Amp
1157 incandescent lamp filament #1: 0.56 Amp
1157 LED lamp "filament" #1: 0.05 Amp
1157 incandescent lamp filament #2: 2.01 Amps
1157 LED lamp "filament" # 2: 0.17 Amp.

As you can see, the differences are quite substantial, but, with the exception of the taillight, these lamps are not a constant drain.
The LED lamps with stock bulb envelopes are about $15.00 each, so they are quite expensive in comparison to the original incandescent ones.
Additionally, in order to eliminate the "hyperflashing" symptom inherent in low-draw LEDs in an incandescent circuit, I purchased a "smart" turn signal relay to replace the original one; that takes care of hyperflashing. That unit was $10.00.


The big drain is the headlamp, which is a 6014 unit in the U.S. headlamp
I, the ignorant one, trusted the vendor Autobaba, in their advertising an LED headlamp that would replace the incandescent 6014; silly me.
Firstly, the vendor has, at best, a poor knowledge of the English language, so corresponding with them to get technical questions answered is frustrating and non-productive.
The LED headlamp from Autobaba has a much larger draw than I had anticipated:

6014 sealed beam low beam: 3.6 Amps
6014 LED lamp low beam: 3.02 Amps
6014 sealed beam high beam: 4.25 Amps
6014 LED lamp high beam: 3.1 Amps

The difference between the two types of lamps here is disappointingly small,
and in my humble opinion does not justify the retrofit. Furthermore, the headlamp must be used with an inline "decoder" box, which smooths the current to the LEDs, because they will flicker when exposed to the pulsating voltage provided by an alternator-driven charging system. The Decoder unit would be a very tight fit into the headlamp shell, and might necessitate relocating the turn signal relay out of the headlamp shell.
finally, not only does that LED unit NOT fit into the ring that captures the lamp ( P/N 0960.38.279; it is slightly too large. additionally, protuberances on the backside of the LED unit interfere with the fitment of the ring that sits behind the lamp (P/N 0960.38.278).

If my sanity prevails, I may look into another item that I have read to be successful: Morimoto Super 7, but it's a
$250 hit, and I can buy a bunch of other goodies with that. I will try to get in touch with them to find out what the current draws are, but it might take a while.

Thus far, the bench testing has been informative, and I hope that this info might be of use to anyone interested in the process.

I am including some pics below, of the 1156, 1157. The 1156 and 1157 LED lamps are ever so slightly taller than the stock ones, as shown in the pics, but not enough to cause interference. The originals produce heat, so the lenses are a bit away from the bulbs. The LEDs run quite cool by comparison.