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Discussion Starter #1
You guys have been great, helped me out on a lot of issues. I have a '78 280z, the washer always blows the fuse. Have FSM, getting awful familiar with BE section. But electrical not my strong suit. Have meter and test light, just not always sure how to use them.
Saw Dave M's video on this issue, visually checked the wire at the combo switch, seems to be ok.
Could really use a step by step on how to locate where this issue is.


thanks much


phil
 

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so it only blows when using the washer? reg wipers ok?
if that is the case start by unplugging the washer motor.
If you have a test light use it IN PLACE of the fuse that keeps blowing.
The idea is the light will glow brightly if there is a short, not as bright if not a short. The wipers may not move due to the resistance of the light, but you matter, you want to see if the connected motor makes it get a lot brighter.


The light acts as a fuse when placed in the fuse circuit. some alligator clips make it easy to connect it in place of the fuse (tip to one side of fuse block, butt end to the other side of the fuse box, fuse out of the box.


The most logical problem will be a seized washer motor. disconnecting it will tell by the brightness of the light (or you could just disconnect and try with a fuse in, I just don't like to blow fuses for no real reason.


Once you have the light acting as a fuse you can try different things to see when it glows full on (indicating a short that would melt a fuse). Don't worry about not having a fuse for protection, the light acts like a fuse to protect the circuit.
 

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Discussion Starter #3
thanks Dave M
a little confused by using test light in place of fuse. i clipped one end as ground to the door hinge. and i just laid the business end (probe) across both ends of fuse holder. it lights up.

with the washer motor disconnected, when i press the washer button, the test light dims.
with the motor connected, again, press button, light dims.

of course, both these instances occurred exactly once. on trying to replicate a second time, the light never dimmed, regardless if motor was connected or not.

btw, with a good fuse, wipers only have fast speed and when turned off, they don't complete cycle, just stop where they are. intermittent does not work, though i hear clicking from what i suppose is wiper intermittent amplifier.
 

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pretend the test light is a fuse. one end of the light to one terminal of the fuse block the other end of the light to the other terminal of the fuse block. You want the current to pass thru the light the same as it does the fuse. You do NOT connect anything to the body ground, that is how you check for voltage, your are trying to check for current (excessive current as is a short). remember NO fuse installed. the whole idea is to use the light as a fuse, instead of blowing it just lights brighter.


OR just put in a new fuse and disconnect the washer motor. Does it still blow, if not its the motor. I just don't like to waste fuses.
 

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Discussion Starter #5
ok, probe is on one end of fuse holder, its wire on other end of holder. press button with motor disconnected or connected, light comes on both times and there is no difference in brightness. does that make sense?

i used my last fuse with motor disconnected, pushed button, fuse blew...
 

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Ok I presume it was the washer motor disconnected. Next disconnect the wiper motor as well (plug near fire wall). So now there would be NO wiper and NO washer. Try the light again, still bright as when every thing was connected?


Might be there is enough current with just a relay to illuminate the light to full brightness. If that is the case a proper amp meter would be needed to really evaluate the current draw as you start disconnecting things. Only problem is most multimeters are only good for 10amp before they blow the internal fuse.


I was hoping you could note a variance in the light intensity to at least narrow down what is causing the excessive current draw. An alternative would be to use a head light bulb, that would be less sensitive than a test light. It would only be very bright if there was a dead short some where.
 

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Discussion Starter #7
sorry, late night last night. didn't realize wiper motor was part of the equation. so...

with both washer motor and wiper motor connected, press washer button, light brightens only a little bit.

with washer motor disconnected and wiper motor still connected, same, light brightens a little when button pressed.



with washer motor connected and wiper motor disconnected, no light until button press.


with both washer motor and wiper motor disconnected, no light until button press.


sorry for being so linear, only way for me to keep this straight in my mind.


i could remove a headlight, or easier, buy a basic one for 10 bucks, if i knew how to hook it up for testing...


thnx
 

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Discussion Starter #14 (Edited)
Both motors disconnected: before even turning switch for wipers, press washer button, fuse blows.
Fuse blows in intermittent, slow and fast positions each time washer button pressed.


also for what its worth, when wiper motor connected, it only runs in the fast position, no slow or intermittent.
 

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Discussion Starter #15
i don't know about the wipers, they now work in all speeds and return to start position when turned off. guess i'll just wait and see if that is an intermittent problem
 

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try unplugging the wiper relay, its the big one on the passenger side under the dash, large plug, also controls the intermittent. if the fuse stops blowing it may be that module that is the problem. Check the FSM to know for sure you have the correct one. I will take another look at it and see if there is a short path thru that module when using the wiper. The fact that the speeds don't work tends to point to it as well.
 

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Capacitor C1 could be a problem if shorted, Its isolated by a diode, so should be able to test. I will see if I can come up with a test for you. term I and E are the ones to focus on.
 

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Discussion Starter #18
Yes, the "intermittent wiper amplifier", on left side of relay cluster, has one 4-prong and one 6-prong plug, unplugged both.

also both motors plugged in, push wiper button, fuse blows
 

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check harness of I pin intermittent amp to ground, should be zero. disconnect amp read harness female. Disconnect car battery before so you don't accidently energize circuit and blow ohm meter.
 
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