I was installing a boost gauge, and must've shorted something out because now my turn signals, fog lights, ac blower, and wipers don't work. I checked the fuses but they weren't blown. How can I pinpoint what the problem is?

UPDATE: This past Saturday I took my time to tackle this problem. I pulled every fuse, everyone checked out. Then I started pulling relays, testing them by wrapping some wire around the 85/86 poles and connecting them to the battery, then testing for continuity between the other poles. Alas I found two dead relays. One, I believe, is the switched power relay and the other is the wiper relay. The stores around me only had the switched power relay. Bought it and replaced it. Lo and behold I start the car and the first thing I hear is the beep from the boost gauge! Everything is now working except for the blower. Not sure if replacing the other relay will fix things as I read that there is none for my car, just the resistor that sits on the blower motor. The make is 99 Audi A4 1.8TQ. Any ideas? Found this wiring diagram: http://autolib.diakom.ru/CAR/Audi/1997/A4/SYSTEM%20WIRING%20DIAGRAMS/fig02.pdf http://autolib.diakom.ru/CAR/Audi/1997/A4/SYSTEM%20WIRING%20DIAGRAMS/fig01.pdf

PS: Its kind of ironic, had I just rushed and put everything back together before testing everything would've been fine!

  • 1
    Electric or mechanical boost gauge? Did you tap into any other cables? Sep 24, 2011 at 0:17
  • Electrical, I tapped into one wire that went into the fuse box (not really sure which, just tested wires with a MM until i found ones with appropriate power), one wire went onto a ring terminal with some other wires (not sure what for), one went to the ambient lighting for the vent, and the ground went to a common ground point.
    – riotburn
    Sep 24, 2011 at 3:55
  • Make, Model, Year? Sep 25, 2011 at 23:31
  • put the make and such in the OP
    – riotburn
    Sep 26, 2011 at 4:30

2 Answers 2


Firstly, get hold of a proper wiring diagram for your car. Disconnect all the wires you have added, and see if that solves the problem. Work methodically back through everything you have changed, as the cause must be in there somewhere if they worked before...

Tapping into random wires without knowing that they are for is always going to be a recipe for disaster. When adding accessories, you should always locate an appropriate feed (either permanent live or ignition-switched-live depending on the accessory) at the point they enter the fuse box, and tap in using proper terminals - never any sort of self-stripping type piggy-back connectors. You should then fit a fuse as soon as possible in your wiring in case of problems. It is usually fine to use any convenient common ground however.


You may have blown a Maxi-Fuse, or fusible link. Get the wiring diagram, more specifically the power distribution diagram and you will likely find all of those accessories are powered from on Maxi-fuse, or fusible link.

I may be able to provide you more assistance if you will update your question with the make model year of your car. It would also be helpful to know what boost gauge you were hooking up, and maybe the directions for it as well.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .