losing voltage

[cc19]

Hello, I have an 87 century with a 230/v8 merc with a tbolt4 ignition, when tested, I have 10 volts at the pos. side of the coil. I have replaced the coil, sensor,battery, wires, plugs,alternator,distrib. cap and rotor, ignition switch. oil and filter, oil/water seperator, fuel filter. When I remove the wire from the pos. side of the coil, it has 12 volts,the ign. switch then has 12 volts, as soon as I reconnect the tbolt4 to the coil it drops to 10 volts and wont start. Sometimes it will read 12 volts and then it will start and run no problem. As you can tell I am no mechanic, but before I replaced the tbolt4 which is kind of pricey I was hoping you could help. Thank you <br />CC

 

[Boatin Bob]

Re: losing voltage

There should be 2 wires going to the + side of the coil, one will only have 12v when the key is in the start position, the other wire should have approx 9v when the key is in the on position because it goes through a resistor wire to drop the voltage. The start wire needs the full 12v to make starting easier (big voltage drop when starter motor is engaged) but then runs on 9v to save coil from burning out. You will need a wiring diagram to help with this problem, do you have a service manual with a diagram in it?

 

[cc19]

Re: losing voltage

There are two wires on the pos. side , one comes from the battery, i guess and it has 12 volts when i test it off the coil, the other comes from the tbolt4. when i connect both to the coil i have 10 volts and it wont start. If you wait around, and fiddle with stuff the pos. side goes to 12 volts and it starts right up. Sorry, no manual, but I have learned quickly what all the wires are.

 

[Fishermark]

Re: losing voltage

Here's a site someone posted awhile back that has a check list for the thunderbolt IV: <br /> troubleshooting