Look at the alt wiring. With no power coming from the alt side, the bulb illuminates
Parasidic Draw on my 1989 F-350 with the 7.3 idi
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IDIBRONCO
IDIBRONCO
And I would assume that it then grounds there too. So the light would light up. I'm not much on electrical things. I know that there are some things that are a ground until the key is turned on. Then they become "hot". For lack of a better term, I call these a switched ground. That must be how this light works too.
johnnolanstrtgld
Registered User
the symbol you have circled is a resistor. I think a diode is a triangle with an extra line at the base.
as an aside you don't need a ground attached to a bulb. you just need a voltage drop across the bulb. for instance one side could read 12V while the other side could be 6V (not ground).
does this make sense?
as an aside you don't need a ground attached to a bulb. you just need a voltage drop across the bulb. for instance one side could read 12V while the other side could be 6V (not ground).
does this make sense?
There is an added wire someone has spliced into the green/ red going to the voltage regulator and according to the schematic there is no other wires. I'm going to check that first thing. I wonder if that wire is putting power to the green/red all the time ? I'm beginning to think this has been a problem with this truck for a long time and that's why I got it so cheap.
This light is suppose to come on with the key in the on position and go off when the motor starts-right now it has power on both sides of the bulb, but I think I might have discovered something-will update after investigating
Glad we can be of help, the bulb lights off of voltage drop. If the harness has been altered its usually easiest to run it back like stock.
I just went out and cut that added wire- THE BULB LIT UP - it's dim, but it lit up. Was it you or maybe someone else on here , said it's very low voltage on that green/red wire. I haven't verified operation yet- got the whole truck apart but the dam thing lit up- I'm excited. YOU did it when you said "No power coming from the alt side" , That made me think about that little wire someone added to the green/red. This truck is a wrecker , so there is a lot of added wires , here and there. There was a lot of Splices and wire nuts , wires just twisted together , all over the truck. I have eliminated 90% of that crap and wired everything correctly. Ok, I am a happy boy, getting dark, gonna eat dinner and hit it hard in the am- will post my findings. And thanks again THEWESPAUL,.......You are the man !
Good looking rig, glad you got it working right!
Ok Wes, Now it's doing the opposite of what it WAS doing. I cut that added wire and the light lit up. I reassembled all the dash (kinda regret doing that), loomed all engine compartment wiring and started the truck. The alternator is charging and everything seems to be doing what it is suppose to , but now the dam battery light is staying on after the engine starts. First I couldn't get it to light , now it wont go off. It's suppose to go out once it gets voltage from the alternator, correct?
That’s right. You’re gonna need to test voltage on both ends of the bulb and see which one is low. My guess is one side of the circuit has high resistance so it is showing less voltage than the other side, causing the bulb to light.
I'm getting good readings coming INTO the dash, but where the power is going OUT of the cluster I'm not getting ANY readings and I'm having other issues with the dash (no tach or fuel unless I push ******* cluster plug)......gonna change out cluster and see if that's the problem. Just did all return lines, leaking like a stuck pig, dam ebay parts ! ordered some "REAL" o rings today.
Macrobb
Full Access Member
When wired correctly, the light provides (limited) power to the regulator to "exite" the alternator. Once the engine spins up, the alternator should be providing power back to the regulator which is then used to power the field in the alternator.
If the light is staying on, either the regulator is shot or the alternator is not providing power, so the regulator doesn't have another power source to draw from.
Also, if you bypass the light(with a wire), the current isn't limited anymore, the regulator gives the alternator too much current(it gets hot) and the regulator overheats.
That bypass wire may have killed the regulator by being there, depending on how long you had the key on with the engine not running for.
If the light is staying on, either the regulator is shot or the alternator is not providing power, so the regulator doesn't have another power source to draw from.
Also, if you bypass the light(with a wire), the current isn't limited anymore, the regulator gives the alternator too much current(it gets hot) and the regulator overheats.
That bypass wire may have killed the regulator by being there, depending on how long you had the key on with the engine not running for.
What if the dash is not taking the power coming back from the reg, which I think is happening.
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