zeiss150 Posted January 2, 2008 Share Posted January 2, 2008 hey guys.... I have a fuse problem... This is what I have 72 240z with a stock wireing harness, 60 amp altinator with internal regulator, zx coil and dizzy (e12-80 module), A new (new to me) fuse block, civic a/c fan (I don't have a/c but I can dream). I was blowing fuses for the tail and dash lights so I tracked down the problem to a rusty marker light housing, I was also blowing the horn/battery fuse and I was wondering if anyone could point me in the direction of finding the short. All of the mods have been in the car for about two years with no problems. I just put in the new fuse block in hopes that it would fix the problem... no such luck. Thanks for your help if you need any more info let me know! Matt- Quote Link to comment Share on other sites More sharing options...
Zmanco Posted January 3, 2008 Share Posted January 3, 2008 The first thing I'd do is remove the connectors from the horns and then see if the fuse blows. If it doesn't, then reattach 1 horn and try again. This will isolate if the problem is with one of the horns, or with the wiring in between. Good luck! Edit: If the fuse blows with both horns disconnected I'd look at the wiring diagram to see what else besides the horns are on that fuse circuit. Quote Link to comment Share on other sites More sharing options...
zeiss150 Posted January 3, 2008 Author Share Posted January 3, 2008 thats the kind of tip that I'm looking for! I tried unpluging both horns and as soon as I put in a 20amp fuse it blew...sooo that didn't work but now I have one less thing to focus on. The battery also runs through that fuse. The cover for the fuse block says that the horn fuse (the one that keeps blowing) and the stop lights fuse (this one doesn't blow) have the battery running through the fuses. the stop lights work just fine. only the Horn fuse is blowing... so why would the battery short the horn fuse but not the stop light fuse that it also runs on???? Help! Thanks guys, Matt- Quote Link to comment Share on other sites More sharing options...
Zmanco Posted January 3, 2008 Share Posted January 3, 2008 Matt, a few things: - what do you mean by your comments about some fuses have the battery running through them? - Even though I have a 73, I just found a 72 wiring diagram which I've attached. It shows there's a relay for the horn. I'd try removing it and seeing if the fuse blows. - I must be blind because I can't find the horn switch (on the steering wheel) on this diagram to see if it's powered by the same fuse. Besides the relay, the horn switch is a moving part and hence a likely candidate to fail due to age, etc. Also, have you done any work around the steering wheel recently? Stay on it - the horn circuit isn't that complicated so you should be able to find the problem. 72_240z_wiring.pdf Quote Link to comment Share on other sites More sharing options...
zeiss150 Posted January 4, 2008 Author Share Posted January 4, 2008 Hey Dan, What I ment by the statment that the battery runs through it is ... both the horn and the stop lights have a common power sorce from the altinator (the white wire) So im sort of thinking that there might be a problem with the white wire ... but then why wouldn't the fuse for the stop lights blow? I'll chase down the relay for the horn. but im also going to look at the altinator connetion The horn is a direct ground circut ... so... it works by grounding the circut, when you push on the horn button it makes contact with a brass "arm" behind the stearing wheel, which compleats the ground. I hope that makes sence. In answer to your question, no i haven't done anything to the stearing colum electronics. I'll keep you posted, Matt- Quote Link to comment Share on other sites More sharing options...
Zmanco Posted January 4, 2008 Share Posted January 4, 2008 I don't think the white wire is the issue as it is just providing power from the battery to one side of the fuse. Earlier you said that the fuse blew as soon as you put it in, even with the horns disconnected (make sure BOTH were disconnected). Find and remove the horn relay. If the fuse still blows, then focus on the wiring between the fuse block and the relay. If it doesn't blow, then focus on the wiring between the relay and the horns. I suppose the relay itself could be bad as well - let me know what you find out and we can go from there. Quote Link to comment Share on other sites More sharing options...
zeiss150 Posted January 4, 2008 Author Share Posted January 4, 2008 Where is the horn relay located? Matt- Quote Link to comment Share on other sites More sharing options...
Zmanco Posted January 4, 2008 Share Posted January 4, 2008 I've never had to trouble shoot mine so don't know where it is. I'd start with the relays under the dash on the passenger side, just ahead of the door opening. Quote Link to comment Share on other sites More sharing options...
zeiss150 Posted January 4, 2008 Author Share Posted January 4, 2008 Ok Dan I found the Relay (its on the driver side) I pulled the wires off and magically no more blown fuse. So I assume that this means my horn relay is bad...right? Matt- Quote Link to comment Share on other sites More sharing options...
Zmanco Posted January 4, 2008 Share Posted January 4, 2008 Matt, that's progress at least! If you have access to a spare relay, swapping it would be the easiest/fastest to confirm that the relay is bad. I will say that I've never seen a relay fail such that it shorts to ground, so I'm suspicious that the problem might be with the wiring between the relay and the horns. You could test the relay if you have a DVM. Measure the resistance across the contacts (from the diagram I posted it looks like it should be the contacts that correspond to the green and green/red wires on the socket). With the relay removed the resistance should be infinite. Then measure the resistance across the coil (should be the other 2 connectors on the relay). It should be somewhere in the neighborhood of 100 ohms. You could also check continuity from the green wire at the socket to the connectors at the horns. Also, with both horns disconnected and the relay out of the socket, measure resistance from the green wire at the socket to ground. If it's anything other than infinite, there's a problem in the wiring between the relay socket and the horns - probably something has cut through the insulation and grounded it. I could go on with scenarios, but if you look at the wiring diagram, you can easily come up with a bunch of scenarios to test that will eventually isolate where the fault is. Keep at it - I'm very curious to hear what you find! Quote Link to comment Share on other sites More sharing options...
zeiss150 Posted January 8, 2008 Author Share Posted January 8, 2008 hey guys ... I fixed the blown horn fuse. It looks like my relay was fine. I tested continuity on all the wires and they checked out ok. so I racked my brain and the best I could come up with is that the relay was making contact with some metal under the dash(it wasn't screwed to the kick wall). so all I had to do is unplug everything and plug it back in and .... problem solved. That was way to easy. But ... Thanks for all the help and I hope that other people can learn something from my fuse adventure. Matt- Quote Link to comment Share on other sites More sharing options...
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