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Tue Oct 17, 2017 3:49 am

I recently acquired this headlight switch, and would like to to test it to be sure its fully functional prior to installing it.

Can someone please share detailed, step by step instructions for testing the switch with a multimeter?

Thank you very much!

Tue Oct 17, 2017 6:22 am

Set multimeter in ohms resistance mode, or in continuity "beep" mode.

See wiring diagram for your year here in the Tech Section https://www.thesamba.com/vw/archives/info/wiringt1.php

5-minute job

Tue Oct 17, 2017 8:34 am

Keep in mind a VOM will only show continuity at low currents. These switches sometimes pass such a test but fail with the higher current of the headlight load. The dash rheostat is also a common failure point.

Tue Oct 17, 2017 8:59 am

it will at least tell you whether to bother installing it or not for final testing.

Tue Oct 17, 2017 9:23 am

tasb wrote: it will at least tel you whether to bother installing it or not for final testing.

Yep.

I'd do the VOM test, the connect it electrically before mounting it on the dash, and see that it works as expected, checking for voltage drops.

Also, make sure all the push-on terminals are clean and tight physically, so you don't get them heating up or falling off from vibration.

Then disconnect the battery, install the switch in the dash, and reconnect the battery. Remember that main red wire is not fused!!

Tue Oct 17, 2017 9:33 am

The way to properly test it is to wire it up as per the wire diagrams, then turn it on, when the lights are on, you then measure the voltage drop across the switch.
to measure the voltage drop, set your volt meter to the ckrrect scale, at least 6 volt scale for 6 volt cars, at least 12 volt for 12 volt cars (a 20 volt max scale for instance would be fine)

now with the light onm connect the positive lead to the power input terminal on the switch, and with the negative lead connect to the power output termknal on the switch. the reading you get should be extremely low, as this reading will be the loss in the voltage to the lights that the switch create, you want a low low loss for this.
I would think something on the order of a tenth of so of a volt would be good, a 12 volt system can handle about two time the loss of that of a 6 volt system.

if the reading is high, you can dissassemble the switch, drill out the rivets, and then clean the contacts, them reassemble with tine screws and nuts. I have done this repair, its not hard (hence dont toss your old defective switch, it can possibly be repaired!)

now there is another thing, if you have a later car, the highbeams are routed thru a relay, so this test will not be valid with high beam, so do the test with low beam for later cars. On my 61 Bug there is no high beam relay so I can perform this test on either high or low beam.

hope your voltage drop test is low, then the switch is good.

another thing, you can perform this voltage drop test across all the componnets in the in the system, you can measure drop across the fuse panel, and each connector. if the voltage drop,is high, then clean that commponnet, this will assure maximum voltage to the bulbs and bright lights. but the circuit must be on and working to measure the drop.

when you have drops in the path of the lights, all the drops across all the connections, switches, fuses etc all add up and the sum is the totaly drop at the bulb. .3 drop here, .6 drop there 1.2 volt over there and that adds up to a totalmof 2.1 volt drop at the bulb, and the bulb will be dim.
you also should measure the drop in the ground, put the positive lead on the grounded bulb body terminal with light on, and the negative lead on the body of the car, that will tell you how much drop is between the bulb and the ground, this shojld also be ideally zero. if not, near zero, then you should clean the ground connection at the body and the connector to the bulb.

good luck.

ps if you have a digital meter, mixxing up the plus and minus meter leads will do no harm to the meter, if mjxxed up you will get a minus sign on the read out, simply ignore that minus sign. if using an analog meter if you get the leads backwards, the meter will peg backwards, and that can harm the meter. thus if using an analog meter it is good practice to rapidly a nd breifly just barely touch the lead to the terminal you want to test, while you observe the meter, if you see the needle deflect backwards, you need to switch leads. a very brief backwards deflection usually wont harm the meter, but if you leave it backwards for long, the meter can be ruined. so with an analong meter always make of habbit of doing a breif touch of the test terminal and observe the needle movement before you decide to finah the test by holding the leads firm on the test point.

lets see some bright lights now!

Tue Oct 17, 2017 9:38 am

Agreed, one can get some idea of how well the switch will work with multimeter, but for absolute answer having a real electrical load will show how bad of voltage drops it will have.

https://www.thesamba.com/vw/forum/viewtopic.php?t=679045&highlight=fuse+box+soldering

Tue Oct 17, 2017 11:01 am

Cusser wrote: Set multimeter in ohms resistance mode, or in continuity "beep" mode.

See wiring diagram for your year here in the Tech Section https://www.thesamba.com/vw/archives/info/wiringt1.php

5-minute job

Maybe I'm too trusting and too naive these days, but if it was mine, I'd actually just install it without testing.