'98 S70, rear defroster switch blows light switch fuse, and all lights go dead

Post by **utilityaudio** » 29 Nov 2016, 13:25

Hello Everyone,
I'm still pretty new to car ownership, having bought my '98 S70 in September.
I have a few small issues as detailed here https://www.matthewsvolvosite.com/forums ... hp?t=78463 but I have a new issue that I noticed on my Thanksgiving drive.

when I try to turn on the Rear-window/mirror Defroster, all of my lights die (Instrument panel, headlights, turn indicators, possibly even brake lights).
replacing the fuse for the headlight switch restores all of my lights, but I'd like to be able to use this system because as the saying goes "Winter is Coming".

the switch is in the bank to the left of the steering wheel, and the bank is slightly pushed into the dashboard, which is already on my list of things I want to fix when I have time. I looked on iPd to see what replacement parts are even available, and found the relay module, but no switch.

I've seen videos on Youtube that detail the Antenna switch mod, so I would imagine that pulling the defroster switch would follow that basic procedure.
I'm fairly handy with a Multi-Meter, so once I have the switch out, I'm fairly confident that I can take accurate measurements of what it's doing.

so... before I go any further into opening this can of worms... what am I getting myself into, and is there anything that I should definitely *Not Do* as I'm going through this?

any and all advice or pointers is welcome.

Thanks!

Post by **abscate** » 29 Nov 2016, 14:06

Check your manual to see what is on that fuse that you replaced. It could be as simple as your defroster is pulling too much current and taking out the rest of that circuit via the fuse. You troubleshoot that by inspecting the wiring to the defroster.

woodchopper · Post by **woodchopper** » 03 Feb 2017, 16:07

utilityaudio, I would like to know if you resolved the fuse issue. I am having the same problem with the headlight fuse, #26, blowing every week or two. I have also used the rear window defrost and had the headlight switch fuse blow afterward, but the defrost is on a separate fuse so I'm not sure if it's related.

Post by **abscate** » 04 Feb 2017, 05:03

Woodchopper...if that is in a wagon, the tailgate wiring loom in the left gate hinge is notorious for wire breaks and causing electrical gremlins

Post by **utilityaudio** » 04 Feb 2017, 12:42

woodchopper wrote:utilityaudio, I would like to know if you resolved the fuse issue. I am having the same problem with the headlight fuse, #26, blowing every week or two. I have also used the rear window defrost and had the headlight switch fuse blow afterward, but the defrost is on a separate fuse so I'm not sure if it's related.

I haven't fixed it yet, the buttons are still pushed into the dash, and I was out of town for 3 weeks. (then it spent a week stolen, and then a week at the mechanic's being inspected by insurance)

woodchopper · Post by **woodchopper** » 05 Feb 2017, 08:54

Thanks for the responses guys. Utility, sorry to hear about the theft and the setback. Abscate, I'm going to test the rear defrost again. It's been over a week now since the fuse blew and I haven't used the rear defrost at all so I could see if that might be the problem. It still seems odd since the rear defrost is on a separate fuse. Robert DIY thinks it is probably the headlight switch but I don't want to spend the $80 - $100 on the switch if it is not that. I will post again if I figure something out.

Post by **abscate** » 05 Feb 2017, 14:53

Sometimes thieves fix your car when they steal it.

Hey, call me an optimist but I have won lottery twice.....

woodchopper · Post by **woodchopper** » 12 Feb 2017, 12:33

Glad someone has luck in the lottery. I have used the rear defrost a couple times for extended period and it did not blow the headlight switch fuse. So it will remain a mystery for now. I guess it's possible, although seemingly unlikely, that the fuses, all being old, were just ready to blow. The headlights cannot be turned off on the Canadian model V70's so there is always current flowing through the headlight system when the car is running. Not sure why they even bothered to put a headlight switch in since it doesn't turn the headlights off.

Post by **utilityaudio** » 13 Feb 2017, 10:56

woodchopper wrote:Glad someone has luck in the lottery. I have used the rear defrost a couple times for extended period and it did not blow the headlight switch fuse. So it will remain a mystery for now. I guess it's possible, although seemingly unlikely, that the fuses, all being old, were just ready to blow. The headlights cannot be turned off on the Canadian model V70's so there is always current flowing through the headlight system when the car is running. Not sure why they even bothered to put a headlight switch in since it doesn't turn the headlights off.

I've replaced the fuse with new ones every time it blew, so probably not due to age.

my Headlight switch is basically to choose between
* having my High-beams be Momentary, Dash/Instrument lights off
and
* High-beams will stay on, and Dash/Instrument lights on.

with an intermediate option of Running Lights only, with Dash/Instrument Lights On

Post by **abscate** » 13 Feb 2017, 11:04

I think that is right for a Canadian Car with mandatory DRL

In the lower 53 colonies, we have a small switch on our P80 headlight switch that lets us turn off DRLs