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#74 LED in rocker switches (fog light)

Fog lamp wiring on his car is from a Bosch Pilot kit. Fog lamp switch is wired how most cars I've seen have been wired.

So, as it stands, at the relay plug:

Red goes to the distribution block with a 15 amp blade fuse installed
Blue is currently wired to the battery - may move it to an ignition switched source or connect it to the headlamp relay
Black wires go to the fog lamps
Yellow goes to the fog lamp switch

At the switch, it's currently wired with the yellow wire coming in on the top, then the jumper that I mentioned earlier going between the lower terminal of the switch into one of the bulbholder terminals. Finally, ground comes off the other bulbholder terminal. It's possible that the original Volvo kits had two ground wires connected, since some of the 1978-80 GT fog lamp switches I've come across have had a piggyback terminal on the lower switch terminal, which would allow the fog lamps to continue working even if the bulb was blown.

As it's wired currently, Dan's comment seems to be the case.
 
John242Ti said:
Fog lamp wiring on his car is from a Bosch Pilot kit. Fog lamp switch is wired how most cars I've seen have been wired.

So, as it stands, at the relay plug:

Red goes to the distribution block with a 15 amp blade fuse installed
Blue is currently wired to the battery - may move it to an ignition switched source or connect it to the headlamp relay
Black wires go to the fog lamps
Yellow goes to the fog lamp switch

At the switch, it's currently wired with the yellow wire coming in on the top, then the jumper that I mentioned earlier going between the lower terminal of the switch into one of the bulbholder terminals. Finally, ground comes off the other bulbholder terminal. It's possible that the original Volvo kits had two ground wires connected, since some of the 1978-80 GT fog lamp switches I've come across have had a piggyback terminal on the lower switch terminal, which would allow the fog lamps to continue working even if the bulb was blown.

As it's wired currently, Dan's comment seems to be the case.
Click to expand...

The switch passes ground from terminal 2 to terminal 1 (to activate the relay) and then to terminal 3 (to light the indicator) via the jumper. The other wire to the bulb holder should get power, not ground.

While I'm no electronical wizard, bobxyz is (I think he's an EE). The indicator light has no effect on the switch.
 
Wire a small regular bulb in parallel to LED somewhere you won't see it (behind the dash). I've seen similar problems with LED's on other cars, like when all the stops are replaced with LED's and that screws up the transmission lock up, cruise control. etc.
 
hiperfauto said:
The switch doesn't depend on the resistance of the indicator light to activate the relay. The LED should light as long as it has proper polarity.

The early cars were wired differently than the later cars. The top 2 poles (1 & 2) are for the relay, the bottom 2 (3 & 4) are for the light. The relay is triggered by a ground. When the switch is activated, the ground signal goes to the indicator light via the short jumper wire. Power for the indicator light and the trigger for the relay comes from the headlight relay so it will only work when the low beams are on. You said this was wired to power all the time.

Early240FogLightWiring.jpg


On later cars, the headlight relay is used as the ground source. This sounds strange, but the relay will only activate if the headlight is off. The ground for the indicator light is connected to the chassis and power comes from the fog light relay. The relay trigger is energized from the fuse box and the ground comes from the switch via the headlight relay. In this configuration, the fog lights can be on with low beams (alt 2), high beams (alt 3) or on all the time (alt 1) if the wire is just connected to ground.

Late240FogLightWiring.jpg


It should be noted that the relay is not the standard 5 pin changeover relay. It has 2 #87 terminals that are energized at the same time. On the early setup, each output goes to a fog light. On the late setup the fog lights are connected together and go to one terminal and the indicator light is powered by the other.
Click to expand...

QFT.
 
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