911 head light switch fuse

[kr3wie]

Hello,

I burnt my head light switch on my 1976 911.

I am awaiting a new one, and a relay, but am also planning on installing a fuse between the switch and the black/blue cable (instruments). However I cannot find any information regarding what Ampere fuse to install. Is anybody able to guide me on this?

Thank you.

[JSV798]

I'm just doing this job too. I think that there are about 12 bulbs at about 2 watts each so that's a total of 24 watts. Dividing by 12 (volts) gives 2 amps maximum , so I have decided to fit a 5 amp fuse but interested to hear what others have to say.

Roy

[FrankM_]

What I put in :
- 3A fuse on instrument lights (but probably bit high since I canged them to LEDs) - on term 58a of the switch
- 3A fuse on terminal K of the switch to the ashray light

[fintstone]

A single 3A is good for all the dash/under dash lights. Connect one end of the fuse pigtail to the switch (58a) terminal and the blue/black wires that were on 58a to the other end. There should be two blue//alack wires on your '76. One to the heater/vent panel control lights, ashtray light and the temp control lever light and the other to the gauge lights.

If you want to add the third wire from 58a, it goes to the Hazard flasher indicator light (glows red).

[JSV798]

Originally Posted by FrankM_

What I put in :
- 3A fuse on instrument lights (but probably bit high since I changed them to LEDs) - on term 58a of the switch
- 3A fuse on terminal K of the switch to the ashtray light

Yes that's what would be expected from the wiring diagram but on my car (1978SC) I could not find a black/blue wire from terminal K. I have a single black/blue that powers the instruments and then also connected to terminal 58A I have a pair of wires, one is black/blue and the other is black/red. If I disconnect this pair the ashtray light and fresh air control unit lights go out. So in my case I needed only one in-line fuse to take care of everything. Maybe there has been some rewiring on my car as the wiring diagram indicates a black/blue connected to terminal K, together with a gray wire.

Roy

[FrankM_]

Originally Posted by JSV798

Yes that's what would be expected from the wiring diagram but on my car (1978SC) I could not find a black/blue wire from terminal K. I have a single black/blue that powers the instruments and then also connected to terminal 58A I have a pair of wires, one is black/blue and the other is black/red. If I disconnect this pair the ashtray light and fresh air control unit lights go out. So in my case I needed only one in-line fuse to take care of everything. Maybe there has been some rewiring on my car as the wiring diagram indicates a black/blue connected to terminal K, together with a gray wire.

Roy

OK, if it works like that, it works ;-). In the '78 schema I can see 2 chains leaving the output from the reostat (inside the light switch) one chain doing ashtray light & heather controls (L15, L16 & L21 - total of 6 bulbs) and the other chain of 8 bulbs are the instrument lights. If the 14 bulbs are on one wire, calculate the load of 14 1.2W bulbs at 12V and select a fuse (plus check wire thickness).

[fintstone]

On my factory diagram for '78, There should be no blue/black on K. Only a gray wire that goes to fuse S2 and then to the license plate lights. It is the same as my post regarding "76 above (unless there is something different for Europe).