challenger starts with a little help.

[Challenger1970]

I have a 72 challenger with a 360 and a msd ready to run dist.The car cranks great but the only way I can keep it running is to put a jumper wire from the battery to coil. the coil seems to get 12v in start position then down to 3v in run then back to 12v.I changed the ballast resistor but still no fix.Could it be a bad ignition switch lossing power between start and run. I figured if the ignition switch was bad I would get no crank.Also once the jumper wire between the battery and coil is taken off the engine quits.

[MEK-Dangerfield]

Sorry I'm not familiar with the MSD setup, but if you are bypassing the ballast resistor, then you will be putting a hurting on your coil eventually and will burn it up. Are you saying the voltage of the "+" side of the coil is fluctuating?

  Mike

[Got JOB]

unwrap the wiring harness from the bulkhead connector 6-8in. There is a 4-way crimp splice on . See if the wires are hard and brittle[ splice is burnt and no good]

[Challenger1970]

I switched the two field wires on the alternator and the car runs fine.If I hook up the tach signal wire to the tach I have the same problem.disconnect it the car runs fine. Also the tach doesn't work no matter what.I converted to the ralleye cluster for the look only hoping that the tach,fuel and speedo work(the rest are new mopar performance gauges oil, temp ,battery).Fuel gauge does not work but I think thats a ground issue.For the speedo I haven't had the car in gear while running (no brakes)so it may work,but the tach does not work. I heard with some ignition systems you need a tach adapter maybe thats my problem.But if the tach has a problem would it screw the coil.Also are the tach connections are, post coil- signal, tab 12v ignition and the case is grounded in the dash.maybe wiring issue? 

[MEK-Dangerfield]

Thanks for the additional info.

   let me tell you about these Mopar tachs, they can kill you, even if they work.  I had a tach that worked, but it took forever to get the engine started.  If I disconnected it, then the engine was fine.  Yeah, at that point the light bulb lit in my head. There was a short on it's circuit board somewhere. I had it rebuilt, and all is well.  So a short in the tach can lower the voltage that you should be getting to the coil. I hope I have helped you here. You have it connected right from your descripition.

  Mike

[Challenger1970]

Thanks for the reply MEKrunner! I thought that I had something wired wrong. Could it be possible that either the tab clip or post connector could be pushed on too far and shorting out since the case is grounded?Also has anyone tried the Real Time Engeneering tach circuit boards?They are supposed to update the tach and eliminate the need for an adapter.

[MEK-Dangerfield]

Thanks for the reply MEKrunner! I thought that I had something wired wrong. Could it be possible that either the tab clip or post connector could be pushed on too far and shorting out since the case is grounded?

I seriously doubt that. If you look at this pic, there are resin spacers underneath those connections. The long post connection goes on top, and the tab on the screw right below it(tab is missing in pic). For what it's worth, these tachs die often. On the Rally gauges, the clock is the first to bite the dust, and the tach second. 

  Mike

[Challenger1970]

Has anyone ever thought of taking the board out of an aftermarket gauge and installing it into a ralleye gauge?I've done a little research and it seems that most tach are the same. Signal in, 12v in,and ground.And there are two wires from the board to tach face meter+ and meter-. I ask this because I have an older autogage tach that is not in use that is supposed to hook up without an adapter(msd).If my ralleye tach is already toast(shorted) Why not try the auto gage board first,(free fix)than I could look into a new board from real time engineering.Or does anyone know why this would not work.

[MEK-Dangerfield]

That doesn't sound like a bad plan if the Autogauge board will fit. The only hitch I can think of is these old Rally tachs have heavy needles, where the after-market gauges are lighter and quicker to respond. This might not be an issue though, I'm just thinking out loud. 

  Mike

[Bullitt-]

makes me think of this post I made although your car starts OK it could be the same kind of issue. http://www.cuda-challenger.com/cc/index.php?topic=22204.0

[Challenger1970]

I think might try the tach but it won't be for a couple of weeks as I want to get the rest of my interior in order.I will let you guys know how it goes.Thanks for all the help.