83 911SC Battery Drain - ???

[wichitaguy57]

I've read a number of threads on this topic so with my multimeter (MM) and the Bentley wiring diagrams in hand; off I go under the front hood.

With the MM in series with the negative terminal and the ground cable this is the reading. Boot light was disconnected. Initial reading was .048 amps with all fuses in place.

Thinking the clock was the problem I went to fuse 18 (Yellow 5 amp) and remove it. Nothing changed in the reading.



Starting at 1, removed each fuse and when I got to fuse 17 (Red 6 amp), the reading dropped. Good.



All the other fuses check out with a .048 amp reading. For some reason I went back and removed fuse 17 and 18 together and an even better result. Fuse 18 removed did nothing by itself, but when removed with fuse 17 the drain is reduced. I don't get that ????



According to Bently: Fuse 17 - Emergency Flashers, Wipers and Defogger. Page 970-17 shows the flashers switch using fuse 17, Wipers/Washer is on page 970-29 using fuse 12,24. Defogger is on page 270-16, fuses 12 and 24.

Fuse 18 - Interior Lights, Clock, Glove Box, Luggage Compartment all on page 970-24.
The interior lights work correctly when opening and closing doors and setting the lights in various off/on positions. My windows will not function once the ignition switch is turned off, but I also don't see a relay in the wiring diagram to support that function. Did 83's have the ability to close the windows with the key in the off position before opening the door? The light bulb in the glove box had been removed and the switch in the middle position. Light in the boot had also been disconnected while doing this trouble shooting

To summarize this: I don't understand the relationship between fuse 17 and 18 especially since removing fuse 18 had no effect on the amp draw by itself.
Not sure about the wiper and the defogger components on fuse 17. I saw a prior post by tirwin asking about a front defogger so I may reach out to him. I'll remove the Flasher switch to see it that has any impact.

Any other ideas?

[wichitaguy57]

Removed the hazard switch and tested with no change in values.

There are two wires coming out the top of the fuse 17. The fuse panel cover has a description list for each position. Fuse 17 is listed as hazard and heated windshield. Windshield had been replace by previous owner, but i don't see anything on the dash switches indicating a heated windshield.

Is the power to the fuse coming in the bottom and out the top?

[sigchuck]

Bump after three years - same issue in my ‘83 SC. Fuse 17 in and I have a .5A draw, out and it’s down to .05. Interestingly enough, when 17 is in and the door is open, draw jumps to 1.0A.

This is with all lights off, frunk light disconnected, clock disconnected, etc.

On the heated windshield, it was activated by pulling out the defogger handle and turning it. Mine also has this switch, and I would think that it would need a relay (similar to the rear defroster). No idea where that relay would be though, but maybe it’s gone bad?