I just wanted to thank everyone for the help with my Nisan Tino wiper problem. I followed Lee's advice and bridged pins 3 & 5 of the relay. The wipers then worked! (Thaks a million, Lee!)
So I guess this points to the relay being at fault. Now I have what I suspect is probably a silly question... If it works fine with the relay pins jumped, why do I need a relay in there at all? Can I just leave it as is, with the pins 3 & 5 bridged?
Is there anything I can try to restore the relay? Are the contacts in there clean-uppable?
Fit a new relay - they should not be expensive from motor factors/ebay
The relay is there to keep the current through the dash board switch wiring down. If you damage that switch/stalk then you are usually into real money.
Said before that the relay is made all the time the ignition is on. If you leave it bridged, the wipers will work at any time. You might even leave the car with them switched on and flatten the battery.
Depends if you can get inside it. If it is a standard type of relay new ones ain't expensive.
In your case it's simply to make sure the wipers only work with the ignition on, in terms of safety it should be fine as it's fed through both a fuse and a fusible link but it would be better to replace it in case they are any unexpected consequences of having circuits powered when they they are not designed to be.
In general terms, they are used, as others have said, to reduce the load on the switch - ie it's usually cheaper and more convenient than using a chunky heavy duty switch and associated wiring.
Think how many amps an ignition switch in a modern car would have to switch if it wasn't for all the relays :)
Mafco (I think it was anyway) used to do a catalogue showing relay replacements by the terminal layouts and pin numbers - I guess with all the factors moving to fully computerized systems these sort of catalogues don't exist any more :(
If you leave it permanently bridged, the wipers will run all the time!
A relay contains a coil which is powered from the wiper switch and which carries just a low current. When the coil is energised, the main contacts close - causing the wipers to run. If either the coil or the contacts are duff, it won't work - except by bridging the contacts. In this case, the relay needs to be replaced. They usually just plug in.
*However* the symptoms will be very similar if there's a problem with the wiper switch or with the wiring between switch and relay. In this case, replacing the relay *won't* fix the problem. You need to bottom out which it is before incurring any expenditure.
The relay functions as a repeater switch. The term originated in early telegraph days where a weak (digital) signal over a long length of line was used to relay a fresh source of voltage over the next stretch of line to extend the circuit beyond what a basic telegraph key could directly send to the receiving sounder at the next station (the extra voltage otherwise needed would increase the contactor gap requirements on the telegraph key and raise the risk of electric shock exposure for the operator - it also allowed the signal to be regenerated before line capacitance introduced severe timing distortion).
Aside from its original function, a relay allows safe operation of high voltage high power electric motors using low voltage low power circuits at the operator controlled panel. It also allows the control of multiple high power devices from a single control panel button.
The uses of relays are many and varied but most commonly relate to isolation of the operator and the low level logic control circuitry from the higher voltages and currents that need to be switched in order to control high power devices.
In a vehicle, the relay is used to control high current devices using low current signals, the voltage usually remains the same safe 12 to
14 volt of the vehicle's supply. Quite often, the relay can provide basic logic gating and control that would otherwise involve mulitpole panel switches and many yards of additional wiring expected to carry several amperes of load current which would generate significant volt drops without resorting to inordinately heavy guage wiring. A basic relay or two, placed strategically can save a small fortune's worth of copper in a typical vehicle's wiring loom.
So, in answer to your question about needing a relay at all, the answer is simply "No." :-)
Getting the wiper motor to run by shorting contacts 3 & 5 was merely a test of the circuit between the relay's contacts and the motor. Now that you know that this part is ok, your next question is "Is it a faulty relay or a wiring fault to the relay's coil?"
Two basic faults are possible with the relay. One is where the coil has gone open circuit, the other is where the contacts fail to close, either because of a mechanical issue that prevents full travel of the contacts or else the contacts themselves having burnt away sufficiently to prevent proper electrical contact.
In either case, a replacement relay will restore the circuit to full functionality (although in the case of contactor trouble, you may be able to dress the contacts with a suitable file and 'bend' adjust the contact springs to compensate and effect a cure. However, it still makes more sense to simply swap it out for a new replacement).
The relay itself may be perfectly fine and is simply failing to receive the controlling signal from the panel switch due to faulty wiring or switches. If you can get someone to operate the wiper switch whilst observing (listening to) the relay, you should be able to ascertain whether the relay is responding (or trying to respond) to the control voltage or not (without a meter or simple test lamp. it's not possible at this stage to determine whether a failure is due to open circuit coil windings or a lack of the wiper start signal).
A pretty failsafe way to apply test voltage (or even grounds) around relay connections is to use a simple test lamp where one end is clipped to the battery positve terminal and the other to an insulated probe contact that you can apply to the relay coil connections.
Most relays only require a fraction of an amp to operate (circa 0.05 to 0.5 amps) a battery backed 12v 6W test lamp should at least cause enough movement of the contactor assembly to either be seen or else heard, if not actually fully operate the relay in question. If you probe a ground return connection the lamp will simply fully light up without danger of excessive short circuit current flow through the wiring.
You can connect the test lamp to the ground return negative terminal of the battery and test for the appearance of control voltages, in this case you'd have your helper operate the wiper switch and look for the lamp to light up in response.
If the lamp lights up ok to this test but the relay fails to react in any way, it's a pretty safe bet that the relay itself is at fault. If the lamp fails to light in response to the operation of the wiper switch, you either have fault in the wiring or the switch.
If the lamp, when connected to the battery positive glows dimly when applied to the 'hot' end of the relay coil which operates (fully or partially) and doesn't completely dim out when your helper turns the wipers on, you're still looking at a wiring or switch fault rather than a faulty relay. An open circuit coil winding would usually[1] fail to produce any lamp glow with this test (other end of the test lamp connected to the ground return negative battery terminal).
[1] There may be other relay coils in parallel and possibly other circuit elements to confuse this test procedure (using a DVM would be just as confused by such complications - more so than a simple test lamp since a DVM, on its voltage range, will quite cheerfully show full battery voltage even via leakage paths of just a few micro-amps which are otherwise totally insignificant to the full and proper operation of the circuits in question).
If a relay develops a short circuited coil fault (a very rare type of failure), this normally results in a blown fuse feeding the control switch panel supply and the lamp test when connected to the plus 12v terminal will show full brightnes whichever end of the coil is probed (assuming positive logic with the 'cold end' of the relay coils wired to ground return - in some cases it's the 'cold end that is switched to a ground return level voltage, typically when some of the controlling logic relies on relay coil wiring to other relay coils or contacts, usually applied as 'hard logic' where any other combinational logic would make absolutely no sense whatsover.
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