Losing voltage while cranking

[chargd72]

All gauges have power and read correctly while the key is in the run position. While in the start position, the starter cranks but the rest of the car loses power. No spark at the plugs either. Anyone have a suggestion on where to start looking?

[b5blue]

Start at the column switch.

[chargd72]

Do you know what wires I can test with a meter in the column harness so I don't have to take the column apart?

[b5blue]

Long white connector strip near column.

[Kern Dog]

It will look like this:

[b5blue]

Best "Test" is to buy an extra switch. Plug it in without installing and see if it works. 

[Kern Dog]

I have several ignition switches that I pulled from cars that I parted out. They are great for diagnosing troubles like this. Sometimes I have had instances where a car won't start while cranking but tries to start just as I'm releasing the key. Many suggest that is a Ballast resistor issue. Sometimes it has been that, sometimes it was the ignition switch or the dash harness wires leading to it.

[chargd72]

I like the ignition switch idea. Hoping that's it since I don't have a ballast resistor.

[Nacho-RT74]

the ign switch got two stages for feed, ign1 which is RUN circuit ( blue wire ) and Ign 2 which is START circuit ( brow wire ). The Ign 2 is designed to bypass the ballast for full power at the coil on that stage, but on that moment while RUN circuit is cut from ign switch, still keeps hot throught the ballast. That's the reason why brake light ( and oil light if standard cluster ) dimms out while cranking. These lights are feeded from RUN circuit.

If ballast is not present, both sources from ign switch need to be spliced together ( normally made at the ballast location ) to be able to feed the coil and ECU if equipped on both stages.

Aside that, it gets two other circuits, which are ACC which only feeds while in RUN ( black wire ), and STARTER ( yellow wire ) which is just to trigger the starter relay.

Need to note 71/74 Rallye clusters get their gauge source from ACC while Standard cluster gets their source from RUN. SO if you have Rallye cluster it is normal the gauges fall out when cranking. Reading your signature your 72 is an SE, it is Rallye cluster

Another failure probabilities are the connections at bulkhead, or simply a cracked wire on those circuits. In my experience I never have got the first ballast failure in 20 years, nor the ign switch and my car was a driver up to 2013. The only failure I have got related to ign switch is the burnt spot at red wire of its harness due a loosen connection at its plug. This burnt spot could be accomplished with a lighter burnt spot on blue wire too.

[chargd72]

Very informative. Thanks for the rundown. I will trace these with a meter to see if I can locate an open.

[Nacho-RT74]

forgot to say, ACC feeds also in ACC position, of course, and would be the only hot wire coming out from ign switch on that stage.