electrical gremlins continue

[rsefczek]

i was coming home from a kids' sporting event, got in the car and started her up. went to turn on the headlights and everything died. now there are no oil/ammeter lights, no key click, nothing. finally got the car towed home today and started tracing power. at the battery 12.74v, at the solenoid/starter post 12.74, at the fuse block in 12.7, ammeter out 12.7, at the other side of the fuse block the ammeter in is 12.7 and key switch out is 12.7. so far so good. i put the key in to test the key switch in (fuse 7 for those following at home with their destec diagram) and suddenly everything except battery in to fuse block and out to ammeter goes to 0v.

now my interpretation says that means something in the ammeter is preventing flow back to the fuse block but only when the keyswitch is on....that makes no logical sense to me in my limited mind. could it be something in the ignition switch?

it's a 71gt with an ottostart relay installed. any and all suggestions welcome!

bob

[ungermm]

I had an ignition problem that turned out to be that the connections of the wires at the amp meter in the dash weren't good. There is a red wire with white stripes that goes from the starter to fuse box and then to the amp meter and a solid red wire from the amp back out to power up everything. You can check the voltage of these two wires which can be found inside the grey wiring harness under the steering column or near the hood release puller. But, first check and clean the battery connections and connections at the starter, then, all the colored plugs that go into the fuse box need to be snapped in place. I've had that problem before too. Jerry

[namba209]

I think Otto already touched on what you're problem may be. The four studs in the fuse panel may be loose or corroded and the initial arcing on the studs, when you turn the key on, could disconnect the electron flow. I would suggest removing each wire and give them a thorough cleaning and retighten them. If the problem still persists, then the problem could be at the ammeter connections. Of course it couldn't hurt to do the same at both ends of the battery cables and chasis grounds. HTH.

[DESTEC]

Bob,

Do your Hazard lights work? If so the Amp meter is O.K. Just a point here. Fuse 7 is not the (complete) output of the ignition switch: FUSES 5, 6, & 7 are. The #12 Black (yes, a hot black wire) wire supplies the input bus bar which powers fuses 5, 6, & 7. And Fuse 4 is the always-hot Clock, Hazard fuse.

Question: what is the 'everything' that goes to 0-volts when the key gets turned on? And what would be hot with the key off except loads off Fuse 4, normally the clock and the hazard lights circuit? Just trying to get a feel for the gremlin.

Quick stuff: rotate some fuses check fuse clip tension; pull the White Steering Column Connector; see if you have 12 Volts at the on the RECEPTACLE pin 4--upper right-most pin. 12 Volts should be present there with or without the key on. (in fact you just took the ignition switch out of the circuit by pulling Steering Column White Connector.

Not sure how ottostart relay is wired in but it would be in the solenoid circuit and should not be part of the Entire GT Electrical goings on.

Let us know what you find out.

[DESTEC]

Bob,
Since it sounds like you have a Volt meter, while you have the White Steering Column Connector pulled: you can check out the Ignition Switch there.

With the meter set to Ohms or Continuity Beeper, put one probe on the White PLUG pin 4. To check the 'run' position of the Ign SW ring pin 1 to pin 2 and put the Ign Sw in the 'run' positon: you should have continuity.

Keep the first probe on pin 4 and move the other probe to pin 3. Turn the Ign Sw to 'crank' it should indicate continuity while holding the switch to 'crank.'

[rsefczek]

Okay, I've tried a few things and have some more info. I pulled the dash to make sure the connectors on the ammeter were okay, tighten and cleaned. I show power in and out of the back of the ammeter with or without the key. BUT at the fuse block where the red wire from the ammeter attaches, I get 0v when the ignition switch is on but power with the switch off!.

JJ, I looked at the diagram again and I should have parking lights since they are attached to the fuse block (always hot) but I don't. No hazards either, but the terminal shows power (fuse 4).

I show power to the white plug, pin 4 and continuity to the steering wheel plug pins 4 to 2 and 3. So it shouldn't be the ignition switch, right?

bb

[baronbors]

I would guess the switch- can you hot wire it to get it started? If it is the switch you can get it re-built at OGTS and then get an OTTO- Start to save the switch. It sure did the trick for me.. I was burning up a Walmart universal switch about every 6 month. Put an Otto- start in 18 months ago and still going strong.

[rsefczek]

Nope, already have the ottostart in the circuit. I'm really puzzled cause it sounds like a short that occurs when the switch is on, just can't find it easily. Thinking it's time to pull the dash out and go through it wire by wire...then (shudder) look at the bird's nest that is the fuse box....

[namba209]

O.K., let's go back to square one. The problem first surfaced when you tried to turn on the headlights. So, how about pulling the single red wire with a spade lug adjacent to the alternator output stud on the fuse panel. This is the power wire for the headlights. Then see what happens. The only area where the ignition switch would come into play could be the turn signal harness which is the black steering column connector. But there would have to be a short in the harness or worse yet, behind the fuse panel.HTH.

J. J. IIRC the OttoStart relay uses the start wire from the ignition switch to power the relay signal which puts battery power through the relay to the starter solenoid, which in turn powers the starter motor and slides the starter pinion into the flywheel.

[DESTEC]

Bob, Before I catch up; go back 4 posts: I made a mistake.

White PLUG pin 1----should read White PLUG pin 4. THAT is the 12V input to the Ignition Switch. Must have been poor lighting. ehh ehh ehh.
Anyway, you've got the drawing and the general intent of my suggestions; so take it away, Bob!

I'll get back to the thread asaic (as soon as I can). Need me, call me anytime Friday at 'work' 772-221-0207 . It is a Fax line but if I can see your caller I.D., I will pick up the phone. The main No. rings at my bosses desk, and that is the end of that story.

JJ

[DESTEC]

NAMBA209,

Ron, thanks for the otto start update. I think that MOD should not be part of Bob's problemo since his problemo is on the RUN side of the ignition Switch and not on the CRANK side of the switch, what do you think.

I do my best thinking about 7A.M. San Diego time, so until then, Via con Dios, muchachos! (just practicing for Mexafornia)

JJ

[namba209]

What's really wierd about this, is the ignition switch shouldn't even come into play in this scenario, but trons do funny things. The only other thing I can see from the schematics, that could cause the problem is an open in the bus bar to fuse #4, dirty connections at the spade lugs or a blown fuse on #4.

[rsefczek]

I thought of the open bus bar too but visually it looked okay and there is voltage at the spade lug. I can try replacing the fuse although, again, it looks okay by my bifocal aided eyes.

If, when the key is switched to run, power then goes out to the dash, could a short somewhere in there cause the problem. or as Ron suggests, could it be somewhere in the headlight relay? But why do I lose voltage reading at the bus bar...stupid electrons!

bob

[Paul]

Always "Ohm" a fuse, they can be bad and look good.....especially to those of us with poor eyes (me? ... Tri-focals)

(Don't you just hate it when someone uses a now for a verb.... sorry I won't do it again )

[DESTEC]

Bob,

Something downstream of Fuses 5,6, OR 7 is pulling your 12Volts down—I think.
(or do last paragraph first, might be quicker)

Your ignition switch check out is good; Here is a suggestion.

Pull Fuses 5, 6, and 7. Do you checks of the 12Volts at the center lower bus bar by installing one fuse at a time. That should help you determine which fused circuit is pulling down the 12Volts.

Then if you can determine which fused circuit is the problem child, PULL all the wires on the output side of suspect fuse and connect the wires one at a time. By process of elimination you should (there’s that word again) be able to nail the shorted circuit.

But, if that scenario was true, why no blown fuses to start with.

Ah, but if the bus bar itself was the problem no fuses would blow and you’d get the same conditions, so: When the fuses 5-7 are removed, check that bus bar to ground to make sure it is not shorted to ground somehow.

[rsefczek]

jj, sounded like a great idea and couldn't wait to get home and try it...alas, even with all the fuses (5,6,7) pulled, the center bus bar goes to 0 when the key switch is turned to run. the only thing left would be the headlight relay switch. any way that could be responsible? when i get a chance i'll try and pull that. right now "she who must be obeyed" requires my presence for dinner.

bob

[namba209]

This is starting to get next to me. So I'll relate to a story that happened to one of my aircraft during the SEA wargames, and a trouble shooting idea. We had an F-4 that would release ONE piece of ordnance, and that was it, even though there may have been multiple bombs and rockets aboard. On the ground, everthing worked perfectly and the malfunction could not be duplicated. We went so far as to jack up the aircraft retract the landing gear, and even thought about running the engines with the aircraft on jacks, but safety concerns prevailed. After going through this problem for weeks and scratching our heads and other places, we asked ourselves just what were we NOT doing that the aircraft was doing airborne. One youngster piped up, we're not closing the canopies, and he was right, all during the troubleshooting process we had the canopies open. So we closed the canopies and lo and behold the problem surfaced. It turned out to be the aft canopy locking linkage rubbed against a wire bundle and pulled a wire out of a splice just enuff that the voltage going through the wire arced once, to release the ordnance slected and then separated from the splice, breaking the circuit. When the canopy was open the wire went back into the splice connector and the circuit was made again.

Now for the current problem, how about bypassing the fusible link at the starter solenoid by running another wire from the solenoid to the stud in the fuse panel it goes to. Then, one wire at a time replace with a jumper wire each of the three remaining wires that go to the studs. It could just be corrosion has done what the canopy linkage did to the F-4.

[rsefczek]

i'm a bit confused, ron. if i'm showing voltage at each of the studs with the keyswitch off, how would setting the key switch to "run" relate to a corroded terminal? just in case, i've already removed, cleaned, and tightened the connectors. i'll give it a try tomorrow, getting too late here to mess around.

bob

[namba209]

Voltage just shows the potential, amps is the working force. Using my previous scenario, the voltage is there until you turn on the key causing "maybe" an arc that won't allow the amperage to flow thereby disconnecting the circuit. I know a shot in the dark, but it's the only viable thing I can think of.

[rsefczek]

okay, started checking some more wires and here's what i found. if i pull the keyswitch wire off the bus bar at f7, there is voltage at the wire and terminals (yay). i reattach it and power at the wire and terminals go to near 0v. if i pull the f5, f6, and f7 fuses i still have near 0v at the terminals. BUT if i pull the resistor wire (f5) and the headlight relay (f6), now i have power at the terminals and keyswitch wire! something in the bus bar for 5, 6, and 7?? something shorting out with the resistor wire or relay? i give up, time to sleep on it and cogitate a while...

bob

[DESTEC]

ah, the transparent coil wire. You might have it. Pul the black wire on the solenoid. It is directly connected to the 3-Ohm transparent coil wire. Does that help. This happended to me once: the the solenoid was shorting my black (hence transparent coil wire to ground) but with the key on and the black solenoid wire touching ground, the transparrent wire started smoking really badly. Code red, luckily I was fast enough to pull the wire off the solenoid before my harness melted.

Don't forget to check the bus bar to ground just for s**ts and grins.
See, I do give out free advice, lots of it, all the time; sometimes it just goes unnoticed.

[rsefczek]

before i try anything and french fry my wires....pull the black wire from the solenoid and test for voltage with the keyswitch on. if that is now good, replace the resistor/black wire?? if so where do you find the resistor wire. my local parts store sure doesn't carry it! if it is that wire, is there a way to bypass it temporarily so i can at least run the car? sorry to be so dense

bob

[namba209]

Bob, I'd check the condition of the resistor wire before you do anything else. Usually it's just stuffed inside the fuel panel. It is a long wire, the length determing the resistance needed at the coil. If it is burnt, stiff with insulation cracking, get rid of it. You can use a ballast resistor from a GM or Chrylser to replace the resistor wire. The function of the wire is to drop voltage from 12V to around 6-9 volts at the coil durinng normal engine running. During the starting cycle the power to the coil comes from the wire off the starter solenoid. HTH.

[DESTEC]

Bob,

IF you pull the black wire on the solenoid and things check out OK from there on out, check the black wire's terminal on the solenoid-to-ground: IT SHOULD READ OPEN. (does not matter if the key is ON or OFF, BUT this terminal WILL have +12 Volts on it when 'cranking'.) If is is grounded there's the problem. But you haven't told me if you have checked the bus bar to ground without Fuses 5, 6, & 7 pulled.

Gotta do that, HOW could it be grounded: I have no idea. But, PUL-ease check that so I can sleep nights.

NOW. I alway get hung up on the +12 Volt side. Check your battery ground REAL well. AND the fuse box main ground at the mounting stud.
It is a No. 12 brown wire: service that connection perhaps suggested earlier. The fact that you have not started any major fires means you are not shorting major amounts of current to ground: so maybe it is the ground side of the house.

I am sure you are getting close.

JJ

[DESTEC]

check bus bar WITH fuses 5, 6, & 7 pulled : )