1970 Fury 904, Do I have wrong/broken Park Neutral Start Switch?

[1970FuryConv]

Park Neutral Start Switch, 904 trans, 3 prong switch: The connector at the switch at the transmission fell off and was dangling under the car. The firewall connector for the backup lights, terminals 2 and 6, at the engine side of the fuse box had to be disconnected in order to remove the dash. Apparently that was enough to jiggle the wire and make the connector fall off at the switch on the transmission. Not much of a connection.

The switch has 3 long prongs. The connector has 3 shallow slots. When the connector is pushed down on the prongs, the connector doesn’t seat against the base of the park neutral start switch. I had another connector from a parts car, which I tried, but it had even less grasp on the 3 prongs.

In testing the Park Neutral start switch, I sometimes was able to get continuity between the center terminal and the transmission housing, sometimes no continuity. I removed the shift linkage rod from the trans lever to see if it was out of adjustment, but found no problems there. I also was able to get 41 ohms resistance between the brown wire at the starter relay and the negative battery post in Park and 100 ohms in Neutral. However, every time I tried to start the car, the engine would not turn over at all. Then I’d measure resistance again from starter relay ground wire to negative battery post, and I’d go back to no continuity. I have not had any problems starting the car with the current park neutral start switch and connector in place over the past 4 years, but I have put less than 1000 miles on the car in that time. I’m wondering if I have the wrong park neutral start switch or a broken switch or both. As always, any help is much appreciated.

 

[Davea Lux]

It looks like it should be the right switch. Have you tested the starter solenoid to be sure it is working? If your are satisfied the solenoid is not defective, a couple of things to check: 1.) Are you sure that the starter switch is completing the circuit to the solenoid? 2.) Check the terminals inside of the plug for the neutral switch for corrosion, you can clean them with a pick to get shiny metal, that insures a good connection. Do the same to the switch terminals. If necessary, take a needle nosed pliers and gently compress the the plug to compress the internal terminals to get a tighter grasp. 3.) Sometimes, the inside of the switch fills up with transmission oil, that results in poor conductivity for the switch. You will need to replace the switch in that case. This is a dual function switch, it operates the backup lights when the vehicle is in reverse, it operates the starter solenoid when the vehicle is in park or neutral. Check the wiring diagram in the FSM for your application to see which terminals perform which function at which position before running continuity checks on the switch.

As always be sure the battery terminals are clean and that the battery is properly charged.

Dave

 

[Big_John]

Your plug isn't seated. It pushes on pretty hard.

 

[david hill]

The outside pins are for the back up lights. Center pin is ground for the starter relay. Ground the center pin in the connector unplugged and see if it starts. The neutral safety switch and the switch connector are prone to failure. If it starts with the center pin grounded, play it safe and replace the neutral safety and the wire connector for a complete fix.

 

[Big_John]

Close that gap and everything will be fine.

 

[1970FuryConv]

Your plug isn't seated. It pushes on pretty hard.

So, does that mean the park neutral start switch is correct for the car?

 

[1970FuryConv]

The outside pins are for the back up lights. Center pin is ground for the starter relay. Ground the center pin in the connector unplugged and see if it starts. The neutral safety switch and the switch connector are prone to failure. If it starts with the center pin grounded, play it safe and replace the neutral safety and the wire connector for a complete fix.

Hi David. The back-up lights/reverse lights work now. I get intermittent ground from the center pin of the switch. If I just ground the center pin of the switch, I won't ground the starter relay and it won't start. The only way I've been able to get it to start is to run a jumper wire from ground to the starter relay ground. Do you mean run a jumper wire from the center pin of the park neutral start switch to the starter relay ground? Many thanks!

 

[Big_John]

So, does that mean the park neutral start switch is correct for the car?

Yes. Unless you've done a transmission change to an earlier version, that is the correct switch for a 1970.

With the plug not seated, you aren't making a good electrical contact.

Of course, the pins all have to be straight etc. Try turning the plug around just for laughs, but ultimately, it just pushes on very hard so it doesn't come off while driving. It must not have been pushed well enough before if it just came off with some tugging on the wires.

While it is possible you have a bad switch, more obvious problem is most likely the cause.

 

[david hill]

Hi David. The back-up lights/reverse lights work now. I get intermittent ground from the center pin of the switch. If I just ground the center pin of the switch, I won't ground the starter relay and it won't start. The only way I've been able to get it to start is to run a jumper wire from ground to the starter relay ground. Do you mean run a jumper wire from the center pin of the park neutral start switch to the starter relay ground? Many thanks!

Unplug the switch connector and ground the center cavity using a back probe pin or a small screw drive w/ a jumper wire to ground. You can make a back probe pin using a butt connector, a sewing needle &small length of wire. See photo.

 

[1970FuryConv]

· My original connector may be rubber, but it feels like hard plastic. Measuring with a dial caliper, I found that the original connector had shrunk to a diameter .05 inch less than the Park neutral start switch diameter. The connector material had hardened so much that pushing it enough to rock the front wheels forward until the trans hit the parking pawl still did not force the connector onto the switch.
· Yesterday, I ordered BWD PT5667, which is a new connector $26.99 from Advance. It is the same size and shape as the original, but the new rubber connector material is flexible. I cut off the old connector. Butt connected the new connector into place. Taped the wires and Butt connectors with black electrical tape. Tested for continuity across all 3 wires. Found resistance of less than 1 ohm for each wire and no shorts to other wires.
· I put the 3 wire harness back into position against the firewall. I reconnected the 2 backup light wires to the firewall connector behind the fuse box and the brown wire from the center pin of the Park neutral start switch to the starter relay ground. I then got under the car and routed the wiring harness back to the Park neutral start switch. The connector did take a little force to push into position, but nothing like the force I used on the original connector.
· Test start: the car started up on the first try. Backup lights work fine. Thanks for the help! Pics of new connector below

 

[david hill]

Unplug the switch connector and ground the center cavity using a back probe pin or a small screw drive w/ a jumper wire to ground. You can make a back probe pin using a butt connector, a sewing needle &small length of wire. See photo.

View attachment 156155

Knew you could do it.