I need some help finding the time delay switch for the interior lights on a 71 300 SEL. I've managed to find it on the wiring diagram, but not a location for it. The entrance light and the dome light are just getting a trickle of voltage,enuogh to measure, but not enough to power any lights. I would like to check the wires before condemning the switch(assuming I can find it). Taking things apart to look for it is asking to break something on a car of this age.

If I read my diagrams right (ref Chilton's 300 SEL 3.5 and 4.5 diagrams)...

a. If you have both the rear dome light when switched on and front reading light (in its "ON" vs off(mid), or door position), you have good hot (30) supply from fuse 1, at whose output tie point you also source the feed to the relay's switched contacts. If not, check fuse (although it also feeds so many other things, you'd know it was bad...) or wires at the fuse panel.

Note: While extracting door switches, below - be careful to not short leads to metal sides of holes or pull them off and lose them inside panel (!)

b. That same fuse point also feeds both your front door switches, via the back of the LF. Gently extract your RF door light switch - check each of the two wires to find good voltage like you got on rear dome light and front reading light (to the locally-switched ON side), as above. Note the colors of its two wires, particularly which one is the hot feed, and which gets voltage only when the door switch button is out/on. (Or identify via any decent color-coded diagram)

c. Gently extract your LF door switch. Note two single wires - they are the hot feed and switched source for the door/headlight/ignition warning buzzer - ignore.

d. Note both a two-wire and a three-wire set of wires on LF's connector. The two-wire pair on switch should have at least one of its wires matching the above-found "hot" feed on the RF switch - the other one is the common source hot feed, also common with the rear dome and locally-switched reading light. Check voltage at that pair/pin. If good, then locate the three-wire group, check voltage on it with LF switch out/"on". Confirm your make-break readings with RF switch, as well.

e. If both/either are feeding the three-wire set, then you're feeding/activating the courtesy and reading light's relay switch's solenoid, and it should be closing and supplying power to both the door contact side of the reading light and the "courtesy light". If NOT - you've (electrically) found your culprit. Physically, you're gonna have to get the answer from a 109 people...

The punch line is: if you can get your reading light feed, and turn it on with the manual slide switch in the on posit, but not in the opposite position, with either door switch open, you've pretty well confirmed your suspicions...

Stan

__________________
stanbabu@3bubbas.com
59 300d
65 250SE/Cpe
70 250/8
72 250C
78 280CE

In the 108's, the relay is omitted; and
[EDITED/CORRECTED] the door switches operate the two lights via hardwiring only, with the LF switch feeding the courtesy light via/off the switched side junction of the RF switch, and the RF switch feeding the reading light via/off the switched side junction of the LF switch.

I doubt seriously that you'd [EDITED] harm anything if you were to jumper your 109's RF door switch's "switched" wire to the courtesy light's hot (not grounded) side, effectively duplicating the 108's wiring with an odd 3rd branch "hanging" at the inop relay. Then your 300's wiring would now also be providing that feed to the reading light switch's "door" side, as well, via the relay's common-tied wiring to both lights. [EDITED] If the relay occasionally works, the voltages applied will appear on the same wire as will the (new) hardwired connections. But doublecheck my logic, on that, in the prints...

Opinions, guys?

Functionally, the only difference I can see between the two is that, in the 109, the switches will both turn on courtesy light AND offer voltage to the reading light's switch via the switching relay; in the 108, either switch provides current directly to one of the two lights, then via the back of the other switch to the second...

As me Pappy used to say, "There's more ways to kill a cat than by lovin' it to death..."

__________________
stanbabu@3bubbas.com
59 300d
65 250SE/Cpe
70 250/8
72 250C
78 280CE

Thanks for all the help. I finally found the offending delay switch almost directly below the master cylinder. It's in there with a row of relays, but it's the only round one. I jumped the white/red wire to the white/green and it all works, just without the delay. I'm glad I don't have to do any wiring repair.I've already had to repair one wire to the light in the kick panel. The owner found a delay switch online and should be bringing it by shortly. Now all that's left to do is fix the air suspension, rich running,spark plug wires,etc....