befu

iTrader: (2)

Hello, so I put a newer style delco alternator in my formula and I believe I hooked it up wrong. The engine will not stop running with the ignition switch. The coil voltage goes on and off when the engine is not running, so it is not like I am backfeeding it through an accessory. I figure it must be from the alternator (I hope).

Below is the schematic of my wiring for the 1986 merc and also a picture of the delco alternator. The red wire on the alternator plug is tied into the batter circuit directly as the original was to sense when the battery needs charging (red/purple wire). The black plug wire is a bit tougher to figure out but I think this is what I have wrong. Per the picture, I hooked the black plug wire up to the purple wire in the harness for "ignition". I believe this is what is back feeding the voltage as this also goes directly to the positive side of the coil.

I believe the black plug wire acts as a ground when the alternator is not working or stopped to activate an idiot light. When it is working, it puts out 12v so the light stays off. I had my doubts about what I did being correct, so I put an inline fuse in there just incase it was tragically wrong!

So, should I just disconnect the black wire in the small plug and leave the red one tied into the battery circuit as the sensor?

Brian

Original Circuit


New alternator backside

dereknkathy

the purple wire is the culprit. it is supposed to exite the motorola to make it charge. it is now somehow hooked up so it is getting voltage
from the alternator. all the purples are spliced together in the harness. when one is hot, ignition is turned on.

befu

iTrader: (2)

yeah, that is kind of what I was thinking. The delco does not need the excitation wire, it had an idiot light wire I guess.

So just unhook the purple wire and try it. That will be easy. Since it reads as a ground when it is not running, I put a fuse in the connection of the purple and black wires, so I will just pull that out.

Thanks, Brian

befu

iTrader: (2)

Well, that did not work. I disconnected the black wire on the back of the alternator from the purple wire in the harness. No spark then. Why does it need this purple wire hooked up to the alternator to spark? Am I missing something obvious?

Anyone else ever upgrade thier alternators?

Brian

dereknkathy

now hook the purple wire to 12 switched with the key. it is supposed to get it's power from key, not alternator.

Mr Maine

Brian,

I know its a bit late now, but why did you go with a 3 wire vs. 1 wire?

Anyway, as stated above the purple wire from the alternator needs to tie into the switched ignition power (the one from the key swicth to the (+) side of coil. This excites the field in the alternator allowing it to charge (a 1 wire does this internally).

The other wire won't be used as its for an idiot light which you don't have.

3rd wire of course goes to starter.

If engine won't shut off then the coil must be getting power from somewhere other than the key and it can't really get it from the purple wire on the alternator because that is just to excite the field.

dereknkathy

it could if it is hooked to the wrong place on the alternator. you could just buy the 1-wire regulator and install it in the alternator. not rocket science. i could talk you thru it.

Steve H

The red or bat "sense" wire can be hot all the time. The purple wire is the exciter wire to the alternator. It is needed to turn the alternator on. However; it may self excite with enough rpm's without the exciter connected. The easiest thing to do at this point is go to an auto parts store and ask for a in line diode. Install it so power only flows to the alternator exciter wire, not back out. That will allow your engine to turn off.

befu

iTrader: (2)

Checked it out again today to confirm the wiring.

I have the black lead of the plug attached to the purple wire in the harness. this goes to the ignition circuit and coil. So when I turn the ignition off, the idiot light wire is supplying 12 volts to the coild, keeping the engine running. This is what I thought was causing it and had mentioned it previously. Now for the odd part:

When I disconnect the black wire off of the back of the alternator from the ignition circuit, it would not run. I still have 12 volts on the coil, but no spark when cranking. What is up with that? I thought all the ignition power was supposed to come through the dash circuit, that way it dies when you turn the key off.

The orange is hooked up correctly to the charge post, alternator is grounded and the red sense wire is tied into the red/purple wire for sensing when the system voltage drops and to start charging. I even checked with a meter, with the battery switch on, I have the 12 volts on the red/pur wire going t the red sense wire.

Also going to work on cleaning battery, switch and other contacts tomorrow to see if a voltage drop is the culprit.

Hopefully Tuesday or Wednesday I can pull the boat out and try it again. It is just odd.

befu

iTrader: (2)

Figured it out. Black wire for the idiot light should not be hooked up as was expected. I had a connection problem that was causing low voltage to the coil and ignition.

Once I got good voltage to the motor, it works just fine without the black wire from the twin plug attached to anything.

Thank you all for the help, Brian