How much voltage across ignition coil?

[jsbhemi]

I was trying to start my truck the first time, and no fuel. Thank goodness we fixed that, but now no spark. I have a Mallory 6AL box wired to an external coil and billet distributor. The 12v keyed hot to the CDI box shows 12.5 volts however, when I check the coil positive it's showing about 8 volts with the key on. I have moved the ground wire on the CDI box twice now. What voltage should I be reading from the coil positive? I would imagine it would be 12 volts.

[jsbhemi]

Could someone check their coil? I don't know where in the hell I'm losing over 4 volts. Maybe I need another coil.

[manyfire]

I had a similar problem, are you running the oem wiring, if so put a relay in and fuse and run directly from the battery. I had fire problems until I did that, I switched the relay but you could use the key hot to activate it. You should have 12 going into the main power, on fact since you are using a 6a box you could leave out the relay since the box has a internal and just run a fused hot wire to the hot in, 85ss just had a similar problem. Read his thread

[Scotty_S-15]

I've got something like Manyfire's suggestion, so obviously its a great idea.:rolleyes:

My problem was a "suspect" ignition switch. Also the relay was a way to get around the problem with engine still running with battery switch off.
.
.

[jsbhemi]

Yes I am running the OEM wiring. I will try the fused hot from the battery.Okay just to be sure you suggesting a fused wire from battery to CDI box hot? What size fuse do I need? Right now I have the positive wire from the ignition box going to the junction block on the firewall.
Thanks guys!

[jsbhemi]

Well I tried the wire straight to the battery and we still get 8 volts on the positive side of the coil. Is this normal? This thing is beginning to make me sick.

[Scotty_S-15]

Well I tried the wire straight to the battery and we still get 8 volts on the positive side of the coil. Is this normal? This thing is beginning to make me sick.
How is the system wired? Normally the coil + gets battery voltage (unless a resistor is required) and the negative wire is the "trigger" wire. Is that Mallory requires and what you've got?

Try disconnecting the wire from the coil and see what you get.... on both the wire itself, then the coil + with the wire off. You see where we're going with this, right?;)
.
.

[spacecadet]

Thinking outloud. 8 volts? Back in the day when there was point ignition there would be a resitor wire that would only allow 8 volts to the points. Might there be a problem with the mallory box? wrong box?
Like I said ... thinking outloud. Don't have a mallory box - so I have no experanice with them.

Space.

[jsbhemi]

How is the system wired? Normally the coil + gets battery voltage (unless a resistor is required) and the negative wire is the "trigger" wire. Is that Mallory requires and what you've got?

Try disconnecting the wire from the coil and see what you get.... on both the wire itself, then the coil + with the wire off. You see where we're going with this, right?;)
.
.

Actually, I'm not really sure where you are going. LOL
I've got the big red wire straight to the battery positive. The big black wire to chassis ground. The small red wire to the original coil positive 12v for a keyed hot. The small black to the negative side of the coil. Orange to the positive side of the coil. Green/purple wires to the plug on the distributor. Yellow to the tach. There is an extra white wire which isn't used on my setup, however could I use it on the coil positive to get 12 volts?

[SassyV8]

what distributer you have? points,magnetic pu . crank trigger?

[jsbhemi]

Its a no name magnetic style from White Performance.

[jsbhemi]

Whew! Just came in from working on the truck all afternoon, and it started! I removed all the old ignition junk and dropped in an old HEI. Played with the timing a little and it finally fired. What a relief. Bad thing is it ran until the fuel in the line was gone, and quit. Now I have to sort out another freakin' fuel problem. Oh well, that's the naturre of the beast.

[SassyV8]

On the other Dist you have, If it magnetic you was sopose to use the white wire. Looked on the Mallory web site and shows how to wire those boogers up. did one for a friend on HEI. It was not so bad taking the time to do it. Mabee try again on the other dist.

[redneckgames]

yeah, Im running probably the same type distributor in mine. If I remember correctly, you wire it completely opposite of what you would think. Dont ask me what Im talking about, cause right now I couldnt say, but there was something odd about the way it wired up. But I, well Dad, pretty much rewired everything under the hood on mine. I should have drew up a schematic of it.