View Full Version : Ignition Switch or Safety Switch

Chris Elzie
05-13-2017, 11:37 PM
I just bought 2 brand new batteries and put on my 73 ambulance and it ran for about 30 seconds, then shut off and would not run after that. I tested the coil and wires going to the coil and I only get fire to the coil when the engine is being turned over, as soon as it starts to run it looses fire and stops. I did run a jumper wire to the coil from the battery and it started right up and ran. Any ideas as to if it might be the ignition switch or the neutral safety switch?
Thanks Chris

John ED Renstrom
05-14-2017, 12:58 AM
The problem is in the run wire. It will be a resister wire or have a resister in it. Odds are good its the switch. The next bad spot is the juction box were it comes threw the fire wall I have seen them loose the connection there. A simple test light will let you see were the loss of power is. It starts off the starter selonad on 12 volts. As soon as that kicks out it looses that source of power. Then it runs off the switch risister​ wire from the switch..so if the run wire is hot to the junction box but not out you know we're the open is. If it's hot out the risister wire is burnt out. But do your self a favor and make sure the connector on the end of the wire is in good shape were it hooked on to the coil. I have seen them only have a strand or two of wire making the connection. Redo that and they run again. But test things first before you start swapping components. You are at least lucky the connection is broken. Tracking down a intermediate one will drive you crazy.

Walter Suiter
05-14-2017, 01:17 AM
Sounds to me like a problem with the circuit coming thru the ballast resistor since it will run with a jumper from battery+ to + on the coil.

Easiest quick & easy in my mind is does the radio work when the key switch is in the run position? If the radio plays I'd do a quick clip jumper across the ballast resistor to check that.

No radio, look at the ignition switch.

Neutral safety doesn't come into play in my mind because it only interrupts the starter relay, and that is working from what I read.

Just minimize run time with the ballast resistor out of the circuit.

John ED Renstrom
05-14-2017, 02:11 PM
the problem is you never know what some one else did. but the 73 should be a resister wire. that's why the test light and start from either end. one way you go till it lights up the other till it goes out. just at that point is the problem. the column switches were not a big problem. they would get out of adjustment or have a broken wire but they did not bun out like the earlier dash ones would.

Paul Steinberg
05-14-2017, 02:18 PM
The 1973 cars, by any GM manufacturer don't have ballast resistors in the system. They rely on a nickel wire that is encased in a cloth covering covered by a plastic covering, that goes from the starter solenoid to the positive side of the ignition coil. There are only a few things that can go wrong with this wire, which are all quite rare, but easy to diagnose. Since you have put 12 volts to the ignition coil, then we can conditionally rule out the ignition switch, ignition coil, and the ignition points. This leaves us with only a few things to check.
1) Has the wire come loose from the ignition coil, or has the terminal end been broken off? Loosen the nut, and then retighten to make certain that there is a good connection.
2) Checking the wire at the starter solenoid, for the same problem as mentioned in number 1, and doing the same loosening and tightening of the nut.
3) Using an ohm meter, check the continuity of the wire from the starter to ignition coil. The wire should be disconnected from both ends to do this test. It should have high resistance since it is dropping the voltage from 12 volts to 6 volts. This is done, so the points are only switching a lower voltage, to keep them from burning out prematurely. GM discontinued this wire at sometime in the 1970, and they used a resistor built into the coil.
4) If the car has a tilt column, the ignition switches sometimes come out of adjustment. Does the ignition switch have spring tension that returns the key to the run position when you let go when it starts?
Finally, you mention that you installed new batteries, might you have disturbed any of the auxiliary wires that might have been attached to the battery cables? I know that on some of my cars, there is a positive wire that comes off the battery cable that goes to the voltage regulator. Not having the luxury of being there to personally examine the patient, diagnosis is difficult to say the least. If I have a 1973 factory service manual, I would have checked the wiring schematic for a more accurate information as to where to start checking. Going from memory, there are a few cars that used a terminal on the ignition switch to supply the coil after the engine has started, and when you turn the car off, that terminal looses power. There is a strong possibility that this is something minor, but tracking it down is going to take some detective work.

Chris Elzie
05-14-2017, 02:30 PM
Its doesnt have a tilt column so thats not an issue.

I have checked the wiring from the coil to the firewall and cant find any bad spots and its hot but only when trying to start the engine as soon as you left of the key and returns to running position it looses fire.

The vacuum had come off the neutral safety switch and when I tried to put it back on the switch came apart, the metal clips on the side broke off. So until I get another one of
those Im stuck.

Walter Suiter
05-14-2017, 02:36 PM
As they always say in the movie when the hero sits next to the bomb with wire cutters,
It's the pink wire, I'm sure it's the pink wire.

In this case, pink is the resistance wire coming direct from run position on the ignition switch to the coil.

Disconnect all 3 wires from + at the coil, switch ignition to run, and check voltage at the coil end of pink.

Worst case if you have a ballast resistor available, leave pink disconnected at the coil + and see if the car keeps running with a jumper wire from battery + to ballast resistor and a second jumper from resistor to coil +.


Paul Steinberg
05-14-2017, 03:16 PM
Its doesnt have a tilt column so thats not an issue.

The vacuum had come off the neutral safety switch and when I tried to put it back on the switch came apart, the metal clips on the side broke off. So until I get another one of
those Im stuck.

The devil is in the details. When that switch came apart, as they all do, you lost the connecting parts to the system. I would suggest that you take a picture of the switch that you have and post it into this thread, along with all the parts, and hopefully you will not be missing any of the parts. There is a strong possibility that some of our members have worked on this switch design in the past, and they can help you with getting it reassembled, and working. Ed had put mine back together when it came apart while he was working on the car. I have been on the lookout for a reasonably priced NOS one to replace it with, since sometimes the back up lights stay on. I have adjusted it numerous times, but it doesn't stay in adjustment. It is just worn out internally. There is a "rebuilt" unit on eBay for $299, which includes a rebuildable core deposit of $50. (http://www.ebay.com/itm/1969-1970-1971-1972-1973-CADILLAC-NEUTRAL-SAFETY-BACK-UP-LIGHT-SWITCH-REBUILT-/382080621234?hash=item58f5c79ab2:g:hOUAAOSwtGlZFiQ B&vxp=mtr)

Walter Suiter
05-14-2017, 05:09 PM

John ED Renstrom
05-14-2017, 10:39 PM
139 for the safety switch. not a lot to them but one will need a little vacuum grease to repair it. the vacuum line is the brake pull off the plastic slide has the contacts and the port for the pull off. you reassemble it and glue the case back gatherer after greasing things.

knowing wha I do now I could have gotten pause to stay with some of the Q-bound and a file. the tab on it is hollow on the edges and has collapsed to the center. just need to square that up and it will stay adjusted.

the wire that is hot when starting is the start wire. there is one more on that terminal that is the run wire. it starts on 12 volts in the start position on the key then in the on position it runs off the resister wire. this wire may be off the starter also it would be the one on the r terminal. the other one would be on the s terminal. as i no longer have a 73 i gave that shop manual to Richard. so I can't look up the wiring for you on that. I take it everything else works with the key in on position? if there is no radio, try the blower motor or wipers.

Chris Elzie
05-14-2017, 11:53 PM
Unfortunately the blower motor wires have been cut, so I disconnected them from the harness in the dash. The radio and the wiper motor are there but not all the way hooked up. The ambulance had everything taken off the firewall to be painted and was never completely reinstalled.
I have had it running prior to all this so none of those wiring issues have prevented it from running before.

Paul Steinberg
05-15-2017, 12:46 AM
If it has been seriously molested, then I would suggest that you start hunting down an original wiring harness off a similar car. the nice thing about GM wiring harness's, is that there are no 2 terminal ends that are identical near each other, so you can't make a mistake when it comes to plugging everything back in. If the dash harness is also molested, then I would buy that one also. The only thing that I know for certain that is different in the engine harness for an ambulance vs. passenger car, is the alternator and regulator wiring.

John ED Renstrom
05-15-2017, 11:09 AM
that sound like sound advice in this case.

Chris Elzie
05-27-2017, 09:13 PM
I put in a new ignition switch and it worked, now I just have to get a new 184 Beacon thanks to a tree limb.