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Discussion Starter #1
I recently bought a 91 Prelude and am experiencing an intermittent short causing the clock fuse under the hood to blow.

I know it was happening to the previous owner because I found an empty 10amp fuse package under the seat and the 10amp under the hood was replaced when I first had to change it.

I have disconnected the radio and clock and still had it blow.
It happens often when I go over a large bump.
After blowing I can replace the fuse and its good to go for awhile.
I recently drove it to Colorado from the Midwest and it didn’t go out for 1000 miles but then on the trip back it was every 15 minutes.

The power antenna is broken, but the previous owner disconnected the motor power on the antenna end, if this is related where is the other end of this power wire?

I am not a car guy, I do computer work.
This is my first vehicle.

My question is this:
Has this happened to anyone before? and whats the common cause?
Otherwise:
How shall I go about finding whats going on?, I have found the prelude3g site and used the manuals there to find out what was on the clock fuse.
Otherwise:
Would a car mechanic be able to fix this?

Thank you for reading. :lol:
 

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This is nothing more than an electrical short.

Nothing special about this chassis that makes it different in regards to electric trouble shooting.

Go to youtube and learn how to trouble shoot an electrical short on a car, there are a lot of those.

Then go to town and find out.
 

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Make sure none of the radio wiring is exposed and shorting without the radio and antenna. The other thing is the ecu on this circuit but the bumps causing this it really sounds like either the wiring where the radio was or antenna to me.
 

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...91 Prelude...intermittent short...causing the clock fuse under the hood to blow.

I have disconnected the radio and clock and still had it blow.
It happens often when I go over a large bump.
After blowing I can replace the fuse and its good to go for awhile.
I recently drove it to Colorado from the Midwest and it didn’t go out for 1000 miles but then on the trip back it was every 15 minutes.
Is this the power distribution diagramme you have? I guess it is fuse #35 in the under hood fuse box that is blowing.
http://media.honda.co.uk/car/owner/media/manuals/PreludeManual/62sf120/16-16.pdf

The power antenna is broken, but the previous owner disconnected the motor power on the antenna end, if this is related where is the other end of this power wire?
Could be a short in this circuit as it is connected to fuse #35. If the previous owner just disconnected the power wire and left a bare wire flailing around, or taped it up to something metal but didn't insulate it properly, this could well be the problem.
Radio & Power antenna wiring diagramme.
http://media.honda.co.uk/car/owner/media/manuals/PreludeManual/62sf120/16-37.pdf

Has this happened to anyone before?
Not to me personally, but we should be able to work through it.

How shall I go about finding whats going on?
Systematically, a process of elimination; same way you fix your computer problems. I'll see if I can find better wiring diagrammes.
In the mean time, look for where the White/Yellow wire connects at the Radio and power antenna, the connection itself may be where the short is. If not, trace the Wht/Yel wire back along the loom, look for any damage to the insulation that could be allowing the wire to short; where the wire goes through bulkheads or over edges are most likely places to find damage. If these are both okay, do the same for the ECU, clock and cooling fan timer. If your car has an automatic transmission, the White/Yellow wire also has a feed to the A/T control unit (this sits alongside the engine ECU).

Engine ECU and A/T control unit locations shown on page 16-3
http://media.honda.co.uk/car/owner/media/manuals/PreludeManual/62sf120/16-2.pdf

Cooling fan timer unit, location shown on page 16-28
Look in 1989 Supplement, Electrical, Cooling Fan Control: Component Location Index.
http://media.honda.co.uk/car/owner/media/manuals/PreludeManual/index.html


Would a car mechanic be able to fix this?
Car mechanic, possibly; auto electrician almost definitely. Have a look in the phone book or search t'interweb for an "auto electrician" in your area.

My initial thought is that the problem will be either at the connection to the radio or the power antenna, because people fit aftermarket stereos and have power antenna problems so these are the connections that generally get messed with. The other connections are hidden out of sight so usually get left alone.

I'd start by making sure the power connections (White wire with thin Yellow stripe) at the radio and antenna are both insulated, no bare wire showing.
 

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Discussion Starter #5 (Edited)
Thanks for the recommendations.

I already taped over the power antenna wire on the antenna end and it still happens so I will look into it further tonight.

EDIT:
I checked the cooling fan control unit wires, wiggled them, nothing.
I checked the radio wires, nothing, I do have an after market radio, I had done a great job doing the harness and had heat shrink-ed it and shit, ill cut that open as a last resort. I doubt its this because of the evidence of clock fuse shorts from the previous owner.
I will check the passenger side ECU's tomorrow.

I did find that the drain pipe for the power antenna was disconnected...
This might explain why it never went out TO colorado but after the snow storms it did.
There was evidence of water at the bottom there, I reconnected the tube, wrapped more shit there in electrical tape then put a rag at the bottom of that pit.

I also went along to all the interior and exterior and pounded with my hand to try cause a short, nothing.
What that DID DO was bend the metal on the passenger door slightly and cause the paint to chip a big chunk off when I opened that door and it snagged on the hinge area (RIP)

Anyways next time I take the car out I'll go over some dirt roads and shit and see what happens.
 

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Discussion Starter #6
Hey is there any wiring diagrams that show splices, splice order, or splice location? And if so is there one of fuse #35 aka Clock fuse? I haven’t gotten a chance to follow all the wire, If I knew where any splices occur I could take components/points of potential error out of the equation.

I hate that this is so intermittent, I really think its related to prevalence of moisture.

My next plan of action is to remove the stereo for awhile just to 100% be sure its not related to that, if it does not short after that the plan is to disconnect the power antenna control wire from the harness. After that I’ll dig deeper into the other stuff.

also sorry for the double post, I'm not sure if editing bumps or whatever and I have to admit I don't have time to re read the rules in their entirety, so if I'm messing up please let me know.
 

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Discussion Starter #8 (Edited)
Alright I'm back again.
Good news! The shorting stoped being intermittent so I purchased this: [ame]http://www.amazon.com/Tool-Aid-25100-Short-Tester/dp/B000RFLR0U/ref=sr_1_1?ie=UTF8&qid=1454220082&sr=8-1&keywords=short+finder[/ame]

And so far found out this:

Previously known:
Pulling hood fuse (Hood fuse #35) stops shorting (This is the fuse that blows)

Now known:

pulling ACG(S) fuse stops shorting (Hood fuse #37)
pulling all relays and other hood (non Main Fuse section) fuses does nothing

pulling harness/connector C-259 stops the shorting
pulling harness/connector C-418 (BLUE) stops the shorting

http://i.imgur.com/1Du2WKN.jpg
http://imgur.com/a/H9meW

I have yet to take the dash back apart.

With what I listed above where should I look next? What components can I rule out?

I'll get back to work tomorrow.
midnight EDIT: Just checked on the car... It has stopped shorting again... Guess I'll have to take another joy ride and hope it comes back...
 

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Here is a clearer diagram of fuse 35 and splices:


I would check the red highlighted bits of wiring as those are where I think they are most easily damaged causing a short:




 

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Discussion Starter #11 (Edited)
Okay the short must be after where C-418/41? becomes blue connector 721 , the power flows from female to male so it must be somewhere in the dash.

in this picture: http://i.imgur.com/fYe9WCi.jpg
idk if you labelled 416/418 right, the arrow looks like its pointing at the long tall one on the left not the blue top connector.
IDK, I might be wrong, 418 is no where on the first diagram but it seems to be that blue connector.

I unplugged the blue one that was causing the short and the radio and the clock still work... I'm not sure how this connector relates to the rest of the stuff that runs off that fuse, I wish it would start shorting again so I could figure it out. I'm still avoiding having to take the dash apart, I don’t have proper tools to lower the steering column again.

Do you have any idea what this connector is for? On the 3G site main wiring diagram blue connector C-418 says "(A/T Only)", is this implying its only in Auto Transmission??
 

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Discussion Starter #13 (Edited)
I don't see a WHT/YEL wire in your blue connector, I don't think it is part of the fuse 35 system.
Huh... Alright well I'll keep looking, I'v started lowering the steering column, hopefully I can get this fixed by the end of the week... I hope the short reveals itsself again.

Hey, I should add that I never mentioned this entire time that the anti lock break system is fucked, as in I had to bend the sensors away from the wheels when I bought the car, It just always shows the warning light... Never looked into it... but do you think it could be related to this fuse?
 

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Discussion Starter #14
Mustard cat, where did you get those diagrams? Is there a way I can find or buy them?

I'm trying to figure out what else is all on that blue connector. C418/C721

Until it shorts again I'm kind of stuck, that connector is the only clue I have.

http://i.imgur.com/TfOtJOg.jpg
 

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Memento Mori
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They are from the Electrical Troubleshooting Manual. I checked it and that connector is just for the shifter position lights in the cluster. It's not related to fuse 35.
 

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you might still be able to buy the electrical troubleshooting manual at http://helminc.com if not then ebay
 

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Discussion Starter #17
It started shorting again, yeah its not the blue connector its the one next to it, I never doubted you for a second :lol:.

I ordered the Electric trouble shooting guide on ebay, ill keep looking at the car until then.
 

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Discussion Starter #18 (Edited)
Alright, I did some more testing.

Using tin foil as shielding, the short finder only reacts over the blue-white wire on the C-719/C-416 connector (The male side, C-719), when this connector is unplugged the shorting stops. When this connector is plugged in and the clock is unplugged it still shorts.

My question is this:

Can you provide any information on what the blue-white wire on C-719 leads to? Otherwise I will wait for the manual.

Again I have yet to take the dash apart, but will if I can get enough hints as I have to reassemble the dash to drive it until it starts shorting again if it stops.

http://i.imgur.com/PIEITNk.jpg
 

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Even if the clock is unplugged the WHT/YEL wire could short on something.

I couldn't fine the BLU/WHT wire in the ETM.
 
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