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I am tidying up some wiring for headlights and I found a relay under the dash. I believe it's a dimmer relay. I have 2 relays for the headlights and I have questions about that, I will get to that later. I lost power to my front signals. I found a wire not connected. I looked everywhere but I don't know where it goes (I think its supposed to be connected to the headlight switch).

So my questions are, Do I need a dimmer relay if I already have 2 relays for the headlights? My headlight relays are 5 pin 87 relays. If I put 87a relays in the headlights don't work right (see picture below).I know the relays are different I would like to use the 87a, they seem more common.

If the turn signal wire is connected to the headlight switch, which spot would it be?

Any help or advice would be appreciated



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Last edited by JB356SR
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JB, two things one should not attempt doing blind and by remote control are brain surgery and automotive wiring — for mainly the same reasons. You could end up with more trouble than you started with.

I won't try to answer your questions directly, but offer some stuff to think about.

- Our cars  come from many different sources, and each one has usually been serviced by many hands before reaching its current state.
- Some of our cars are wired like old VW's, some sort of  like old VW's (but not exactly), and some not at all like old VW's. So it's impossible to tell, from here, exactly what you've got, and therefore what specific advice to give.

That said, our headlights are frequently controlled by circuits using two different types of relays. One (which I'll call a 'traditional' relay) is often used to control a high-power circuit (like headlights) with a circuit you'd like to run only small current through (like your headlight switch). Both of the relays you show look like that kind of relay.

Another kind of relay is called a 'latching' relay (often called a 'dipping' or 'dimming' relay). In VW's, it's almost always used to switch headlights between high and low beams. The headlight switch sends power to the latching relay, which in turn sends it to the high or low beams.

Here is a typical latching relay. Notice that the pins are labeled differently than on the 'traditional' relay:


Generally the wire from your headlight switch goes to '56', the wire out to your low beam goes to '56B', and the wire to your high beam goes to '56A'. A 'hot' wire from the fusebox goes to '30' and the magic wire that controls the switching goes to 'S'.

You can switch between high and low beams, and back again, by momentarily touching 'S' to any electrical ground. In a VW, that function is usually done by a push button on the end of the turn signal stalk, but any 'momentary' (spring-loaded) on-off switch will work.

If none of this makes any sense to you, it's probably best to call in some local support.

Our cars are wired a whole lot simpler than modern cars, so are generally a lot easier to work on electrically, but sometimes clearing away the forest of wiring left behind by previous hands is the best way to start.

If you're allergic to smoke, asking before doing is often best.



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Last edited by Sacto Mitch

Thank you Sacto Mitch for the  explanation of the dimming relay, I really appreciate it. Everything makes more sense. I believe my car has the wiring of a VW but not exactly. I have been following  a VW wiring diagram and comparing it to my car and a lot looks similar. I just want to keep things in good working order without causing any damage. I am always trying to improve my car to keep it as reliable  as I can and if there is any good modern upgrades (electric fuel pump, electronic ignition) I will consider them. Electrical has been challenging for me. I send more time reading than doing which is fine but I still run into road blocks like my front turn signal wire.  

I guess more reading and research.

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