Loosing 12v when key turns to crank

[colonel mustard]

No start update.
I tested for 12V (with key turned to ACC) at the ignition spot at the fuse panel. I do indeed have 12 v.
Then I checked for 12v going into the ignition switch (not the cylinder but the actual switch). I do have 12 v.
When I turn the key to crank, I lose the 12v to the ignition spot on the fuse panel.

Any help would be greatly appreciated.




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[75gmck25]

So you are testing for voltage the sliding switch that is mounted in the lower part of the column?

The key cylinder has a gear on the end that turns a toothed rack that is meshed with the end of cylinder (like two gears meshing). The rack then pulls a rod that runs up and down the column. The other end of that rod slides the electrical contacts mounted in the lower column, and makes all the connections.

The ignition rack is made of pot metal, and it sometimes fractures just enough to let it pull away from the gear on the switch, and then you have too much play. This means the rod for the ignition switch may not move accurately enough to line up all the contacts in the switch.

A new GM ignition rack is only about $12-$15, and most parts stores have them in the Help! area, or maybe behind the counter. The catch is that you have to do quite a bit of column disassembly to get to the rack area and replace it. There are many articles and youtube videos on how to pull apart a GM column, and its not that hard. Make sure you tighten up and locktite the bolts as you reassemble, and I would probably also replace the turn signal switch at the same time.

Bruce

 

[Rickf]

Are you dealing with a 1981 K5 or something different? My 1974 K20 had the same issue, it was originally a points distributor system.

 

[HotRodPC]

Are you dealing with a 1981 K5 or something different? My 1974 K20 had the same issue, it was originally a points distributor system.

While you are correct and this does make a difference, even with a points dizzy system you get 12v volts while cranking then once the engine starts the voltage to the dizzy/coil is cut to 6 volts usually by a resistor or resistor wire and sometimes done via the starter solenoid also. Once you go to HEI dizzy, then it should be 12v all the way accross all circuits at the switch, ACC, Run, Start etc.

 

[Matt69olds]

You should have power on the pink wire on the ignition switch with the key in run, and start. If you loose the power on the pink wire in the crank position, I would think you have a defective ignition switch. I’m familiar with cracked or broken ignition racks, before replacing the switch you might try adjusting the switch. If works ok after adjustment, either the switch moved, or the rack is defective. The rack can be a pain to replace, a little wheel bearing grease can help hold parts in place.

 

[HotRodPC]

You should have power on the pink wire on the ignition switch with the key in run, and run. If you loose the power on the pink wire in the crank position, I would think you have a defective ignition switch. I’m familiar with cracked or broken ignition racks, before replacing the switch you might try adjusting the switch. If works ok after adjustment, either the switch moved, or the rack is defective. The rack can be a pain to replace, a little wheel bearing grease can help home parts in place.

It CAN BE A PAIN? It IS a total pain in the ass and other places too. Been there done a couple.

 

[chengny]

No start update.
I tested for 12V (with key turned to ACC) at the ignition spot at the fuse panel. I do indeed have 12 v.
Then I checked for 12v going into the ignition switch (not the cylinder but the actual switch). I do have 12 v.
When I turn the key to crank, I lose the 12v to the ignition spot on the fuse panel.

Any help would be greatly appreciated.

It is rare, but the starter or solenoid can develop an internal short to their casings (which are grounded). When the ignition switch is moved to START, the voltage across the whole system is pulled down. If you have a spare starter, you might try changing it out and see what happens.

Another way to determine if the starter group is causing a system wide voltage drop (one that is severe enough to prevent ignition) without pulling anything apart or buying anything, is to provide a temporary external 12 volt supply to the coil primary.

It's is easy enough to do; use a battery charger or a separate, independent battery and run a jumper from the positive to the B+ terminal on the coil (be sure to disconnect the installed wire or the independent supply may be pulled down as well) and ground the negative to the frame.

 

[Matt69olds]

It CAN BE A PAIN? It IS a total pain in the ass and other places too. Been there done a couple.

Nonsense!! Steering columns are easy to work on!! All you need is few extra hands with tiny fingers to hold the parts in just the right position to slide back together. No problem!!!

 

[colonel mustard]

thanks for the replies yall, I took the day off work and started testing everything. after about an hour of probing I decided to change out the ignition switch....it is now alive. crazy and a huge coincidence it failed the day after I installed new gauges and redid a lot of wiring to basically bypass the factory gauge harness. I was thinking I did something wrong....

but nope...just a failed 30 year old part.

 

[HotRodPC]

thanks for the replies yall, I took the day off work and started testing everything. after about an hour of probing I decided to change out the ignition switch....it is now alive. crazy and a huge coincidence it failed the day after I installed new gauges and redid a lot of wiring to basically bypass the factory gauge harness. I was thinking I did something wrong....

but nope...just a failed 30 year old part.

Great, Thanks for the update and conclusion.

 

[Snoots]

Nonsense!! Steering columns are easy to work on!! All you need is few extra hands with tiny fingers to hold the parts in just the right position to slide back together. No problem!!!

My! Aren't you a bright ray of f**king sunshine!

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[Matt69olds]

My! Aren't you a bright ray of f**king sunshine!

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Yes I am!! I have a black belt in sarcasm.

It hasn’t been long enough for me to forget the hassle and frustration of my first steering column repair. It gets easier with practice. But who wants to practice that?!

 

[Snoots]

Ditto

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[WHEELMAN]

You are losing your ground.battery ground or else where.