ign switch and alt problems

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IAM-LDS-2

Well-known member
Joined
Feb 14, 2008
Messages
449
Location
Dover Dela - ware ?
When I turn my ign key to off while engine is running , nothing happens . Engine keeps running for 15 to 20 seconds , then engine slowly shuts down and finally shuts off . Ign switch has been in truck for about 10 years ,truck has only 7K miles on a complete rebuild of everything . Tried used switch that was working when removed and brand new Ron Frances ign switch . Same thing with both of them . Where do we look next ?

2nd problem : Alt gauge - also was new when installed and always worked - was showing almost no charge , a check at the NEW battery showed no charge arriving to it . Took the also new - when installed - Delco Alt to a NAPA shop and it tested perfect .What do we check next ?

I am also going to rewire and install a new fuse box behind the seat . Original wiring kit was kinda hokie and fuse box on fire wall under the dash is way too hard for my old body to access .
I am also planning to sell the truck this year and want it to be "right " for the next owner .
Willing to try any and all suggestions at this point .
 
Keeps running: Sounds like it is back feeding power through a fan. I don't know the theory behind it, but my Olds was doing that when my cooling fan was running and one of the shifters at work does it also when the heater fan is on.

Unfortunately I don't remember what was wrong or how I fixed it.
 
The way to check this problem is try to remove the alternator plug at the alternator right after you shut the key off. Not the big positive wire, but the plug for the field exciter wire. The motor should shut off if the alternator is causing the problem. It it doesn't shut off, the problem is something other than the alternator. OEM harnesses have a resistor wire that keep this from happening. After market harnesses may have to have a diode added in line to the alternator to keep this from happening.
 
Does sound like a fan problem, You running any fans without a relay? they become a generator when the key is turned off and back feed the ign until the rpms slow down enough to quit putting out voltage.
If you are not having fan problems your alt may be back feeding the Ign exiter wire.but usually that will stay running.
 
I agree with Smallfoot, on the different alternator wiring.
I don't have any experience with electric fans but I can understand 'the electric fan motor becoming a generator part.'
 
I think smallfoot nailed it , I usually wire alt. through a 194 bulb lights when not charging goes out when voltage is equal on both posts , if there is resistor in line the back feed will keep it going.
 
I second the electric fan becoming a generator, have had that happen before. If it's on when you shut down the engine, as long as the blades turn, the engine will run until the fan slows enough that it's not producing current. I had a light wired up on mine, it would light up going down the road when the wind was turning the fan. I ended up putting a manual fan on, solved the problem.

As to the Battery gauge, is it a voltmeter or ammeter? A volt meter should show an increase in voltage as soon as the alternator starts charging. A ammeter only shows you have current moving, charging or discharging. I have seen some that barely move the needle off the center no matter how much current flows through it. Really, they are dangerous if you have all the battery current flowing through them. One short, and you could melt the wiring harness or burn down the car. They make a shunt style ammeter that only measures a portion of the current flow, much better and safer than the old style.
 
Does sound like a fan problem, You running any fans without a relay? they become a generator when the key is turned off and back feed the ign until the rpms slow down enough to quit putting out voltage.
If you are not having fan problems your alt may be back feeding the Ign exiter wire.but usually that will stay running.
At one time the fan had a relay , I removed it -at this point i know not why . However i have a new relay that I bought -sometime - laying on my bench -still don't remember what happened . i must have wired the fan up without the relay for some reason and as i never used the truck -I was having too much fun with the rat rod I had built I guess - I just do not remember what happened . So my plan is to disable the fan electricaly and see if it is the fan acting as a generator . At same time i will check my dash guage to see if this has any effect on the reading . Thanks for the feed back guys . This should work as there was no problem until i removed the relay .
 
Disconnected my fan ground wire so no fan when switch is on . Started the engine , then turned key off and engine shut right down as it always used too Also while engine was running I checked the alt gauge , it was no longer in the red and was in the green . Thanks for the quick spot on advice gentlemen .

Next is to find the short . I had all my electrical info -including as built schematics and a diagram of the fuse block identifying all my circuits etc. - in a big baggie for safe keeping .Some time during the last 8 years this info has gone AWOL I am sure it is somewhere in the garage under something . I have searched the garage two times with no success . I guess by the process of elimination - pulling each fuse and seeing what does not work - I will be able to ID each circuit . To make matters worse the wires have no ID on them ,so i will be going by color only . Is there an easy way too do this ?
 
For finding a short or unwanted draw this works well.

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Thank you very much , will do this in the AM Sunday. What will be the easiest/best/quickest way to find the short / drain . Will the item being supplied power by this circuit be working or not .Can you have a short / drain with out blowing the fuse . Could you run a temporary wire bypassing the "bad " wire . Or is there some other method i should use ,
 
Thank you very much , will do this in the AM Sunday. What will be the easiest/best/quickest way to find the short / drain . Will the item being supplied power by this circuit be working or not .Can you have a short / drain with out blowing the fuse . Could you run a temporary wire bypassing the "bad " wire . Or is there some other method i should use ,

Depending on the short,some will blow fuses others will just create a drain, like bad diodes in and Alt. or a glove box, brake light or hood light staying on. The main thing is find what circuit is causing the problem then track it down.
 
For finding a short or unwanted draw this works well.

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I tried the fuse removal route and light stayed on for all of them .
I guess it's test the circuits next . Not quite sure how to do that . My thinking says , power comes into the fuse box ,passes thru a fuse and goes out thru a wire to whatever it powers . Is that called a circuit ? , With the fuse pulled - as in step one - is not the circuit fed by that fuse now dead . I could go to each fuse and detach the wire ( circuit ) making it dead , but isn't that the same thing that happens when the fuse is pilled ?
 
You are correct. There is something causing power draw outside your fused circuits. Do you have a radio, clock, etc. with memory hooked straight to battery power? That needs to be disconnected before checking fuses.

Does the electric fan run through the fuse block? Otherwise about the only other circuits that normally run straight to the battery are the alternator and starter circuits. Maybe the horn. And, of course, the wires feeding to the fuse block.
 
Disconnected my fan ground wire so no fan when switch is on . Started the engine , then turned key off and engine shut right down as it always used too Also while engine was running I checked the alt gauge , it was no longer in the red and was in the green . Thanks for the quick spot on advice gentlemen .

Next is to find the short . I had all my electrical info -including as built schematics and a diagram of the fuse block identifying all my circuits etc. - in a big baggie for safe keeping .Some time during the last 8 years this info has gone AWOL I am sure it is somewhere in the garage under something . I have searched the garage two times with no success . I guess by the process of elimination - pulling each fuse and seeing what does not work - I will be able to ID each circuit . To make matters worse the wires have no ID on them ,so i will be going by color only . Is there an easy way too do this ?

Ok on the fan issue! I don't run electric fans but I can see that happening on something without a relay. What has me confused is the quoted post above. If you isolated the fan and the shutdown sequence went back to normal and the gauge quit showing discharge, what "short" are you looking for? I would re-install a relay to the fan, hook it back up. Run the motor and then check to see if it shuts down like it should again and that the discharge is no longer there. If the shutdown goes ok and the gauge doesn't read discharge...you're good right? Say if the shutdown goes good, but the gauge reads to discharge again, I'd say you have a problem in the fan itself. Seems like I remember one of our forum members here chasing an internal problem with a fan not long ago having a discharge issue. Maybe 8liter beater but my memory isn't that great...
 
Ok on the fan issue! I don't run electric fans but I can see that happening on something without a relay. What has me confused is the quoted post above. If you isolated the fan and the shutdown sequence went back to normal and the gauge quit showing discharge, what "short" are you looking for? I would re-install a relay to the fan, hook it back up. Run the motor and then check to see if it shuts down like it should again and that the discharge is no longer there. If the shutdown goes ok and the gauge doesn't read discharge...you're good right? Say if the shutdown goes good, but the gauge reads to discharge again, I'd say you have a problem in the fan itself. Seems like I remember one of our forum members here chasing an internal problem with a fan not long ago having a discharge issue. Maybe 8liter beater but my memory isn't that great...[/QUO

In addition to the ign switch problem which appears to be solved i had something draining the battery . So the short problem i mentioned was an additional issue . However i am going to re-install a relay while chasing the drain issue .
 
In addition to the ign switch problem which appears to be solved i had something draining the battery . So the short problem i mentioned was an additional issue . However i am going to re-install a relay while chasing the drain issue .

sneakysnake mentioned ALT diodes. The ALT can charge properly with a bad diode... as a diode is essentially a one-way-valve, it could "hang open" and allow the current to drain back. I would disconnect the ALT to eliminate the question...

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sneakysnake mentioned ALT diodes. The ALT can charge properly with a bad diode... as a diode is essentially a one-way-valve, it could "hang open" and allow the current to drain back. I would disconnect the ALT to eliminate the question...

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Doc , would that be done with the key in the off position ? Would that have shown up when i had the Alt tested
Ok , did a quick follow up ,Using SS method ,I pulled the plug type connection and the light on my tester was still on The other wire is attached by a nut ,took it off and my tester light was off . So i guess it means I have a bad diode . Does that mean a whole new Alt is needed or can the bad diode be replaced . Obviously this did not show up when Alt was tested at local NAPA store . Would a bench test at an Alternator repair shop show a bad diode ?
Could the diode be tested and replaced with the Alt in the truck ,which would be a lot easier .
 
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The Alt can rebuilt, or just replace the diode trio, usually easier to just swap out the Alt.
 
The Alt can rebuilt, or just replace the diode trio, usually easier to just swap out the Alt.
A trip around town this am reveals all of the mom and pop generator /alt shops have dissapeared . most due to death of owners . Every place I went , said they just replace em . No fix em shops left . Gonna look around a bit more before i give in and buy a new one .My new relay did not come with a built in probe and rheostat to allow a on off range for the fan . Had to order one that probably won't be here till after the holiday . So for now project is on hold .
 

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