928Quest

I bought some LED replacement lamps from Nicole at Sharktoberfest. Enough to do all of the interior lighting plus under the hood (7 total). My model year, 91, comes with factory under hood light.

Nicole mentioned that in her car the under hood light stays on (but dim) when the hood is closed (or switch manually depressed).

And yes, mine does too. So I made some measurements and came to some conclusions that I thought I'd share here for anyone thinking of doing the same.

First of all the LED lights are very efficient as compared to the incandescent. I measured the current draw of the incandescent and the LED substitute.

Incandescent ~700ma
LED ~35ma

Wow, when you think that I have six interior lights, not counting the hood light, you get 4.2 amps current draw just from opening a door with the incandescent and only 0.21 amp current draw with the LED's in place.

The under hood light stays on probably because there is a "pull-up" resistor in the alarm unit. The small current leaked by the pull up resistor can't light the incandescent but does light the LED. Current used during this condition is less than 0.001 amp (<1ma) but still enough to make light from the LED's. The alarm still seems to function normally.

I don't think it's a problem and unless you are the type that likes to cut a hole in the refrigerator door to see if the light goes out, it should not bother you.

I also have the gauge bulbs to replace plus the AC/Heat bulb to replace. So far I think I like the change.

checkmate1996

In my experience, a single LED for the back of the HVAC unit doesn't work well. The incandescent actually works better for this application and the also for the hazard light. To that end, Ademan did a nice writeup on doing LEDs for your HVAC unit which involves some custumization but a better end result.

Good luck

Alan

Chuck - https://rennlist.com/forums/showthre...eferrerid=6055

Try the extra resistor.

I don't think its a simple as a pull-up Rx - in this case the bulb is the pull up (on the power side) the switch is to ground. It may be voltage drop related - can you measure the voltage drop over the LED bulb when on
(batt to the lower voltage LED bulb terminal.

I'm guessing there are several volts dropped there and whatever senses the voltage levels (alarm/fan controller) doesn't like it. The incandescent bulb will pull these inputs high (batt voltage) very hard when its off - the LED bulb very weakly and to a lower voltage.

Alan

A parallel high resistance may be enough to eliminate this

borland

This is a 91’ and up problem where hood light power comes from the constant 12V supply bus 30.

You don’t have this problem on the 90’ S4/GT and below, where the hood lighting power is from the outside light switch on the pod. Also on these earlier cars, the hood light is grounded directly to the hood through a mercury tilt switch.

I think the 91+ alarm controller only cares about the state of the hood switch for alarming purposes, and not the electrical state of the hood light.

After looking at the WSM wiring diagrams, I see three possible LED workarounds:

- Reroute 12v power to the light switch at the central electronic (CE) panel, RE/YE wire from K14 to Connector J22 (open), and reroute the hood light ground wire (BR/GN) directly to the hood. This arrangement would act the same as the 90’ S4/GT which require switching ON the outside light switch to power the hood light, however since there is no mercury switch, the LED hood light would be ON whenever the outside lights are on regardless of hood position.

- Add a ON-OFF switch (SPST) at the hood light to switch off the light.

- Defeat the hood alarm feature, by disconnecting alarm controller pin 5 (engine hood) BR/GN wire at the controller, or at connector T33.

I guess another is to just ignore the problem as no big deal.

c_span

As Alan suggested above, fitting a resistor in parallel with the LED light cluster seems to do the trick (I used 220 Ohms)