Intermittent ignition problems

[EastRidge]

Well, i haven't had my M37 8 months and had to have my wife tow me home.......

On our way into town for an "ice cream" run, the truck, sputtered twice. At 40 mph, died, cam back.....drove on died and came back. Went another 4 miles into town without a hiccup. I thought I say the gauges "flicker".

Got our order, and parked. Started for home, and it died on the street.

The engine cranks,but the gauges are dead, so no indication of spark.

Sitting and turning the ignition switch off and on....it would start, the die.

I was in the cab, switch was on, and the gauges came up, tried to start, then it fired but died immediately.

Towed it home, and while being towed I tried the ignition switch like 10x and the gauges came up....

Got home, gauges would come up with the switch turned on, started, and drive 20 feet, then died again.

I am assuming (hoping) it's the ignition switch being worn out and making intermittent contact.

Help on diagnosis, as well tips on testing the switch.

In the event it IS the ignition switch....what is the best alternative to a stock replacement at $95.00.....as this doesn't need to hold on to being original.

Thank you in advance....gave as much of the symptoms as I could.

 

[NDT]

Suggest you “hot waire” the ign switch leads together to eliminate that possibility

 

[EastRidge]

Suggest you “hot waire” the ign switch leads together to eliminate that possibility

I haven't taken the switch out, but from feeling around in the parking lot....there's 3 wires..... one coming from the big regulator box under the hood, one going to the spider harness for gauges, and one to the coil????

Thanks for the response.

 

[John Mc]

Just about any switch will work. A DPST (Double Pole Single Throw) toggle switch would be fine, if you don't care about looks. In fact, it would be a cheap way to troubleshoot the problem, since the switches only cost a few bucks. The power feed to the switch is wire #11. Connect that to both poles of the switch. The other end of the switch would have the wire feeding the distributor on one pole, and the wire feeding the guges on the other. (I'm not sure why they are fed independently, but that is how the stock ignition switch works.)

Even before replacing the switch, you could just check if the power feed to the distributor (wire #12) has power when the ignition switch is on when the engine will not fire. If there is power there, and the engine is not firing, the problem is something other than the ignition switch.

One other possibility to consider: When the coil starts to go, it can get intermittent, and especially can be affected by heat. Coils can get damaged if the ignition is left on with the engine not running for an extended time.

 

[John Mc]

I haven't taken the switch out, but from feeling around in the parking lot....there's 3 wires..... one coming from the big regulator box under the hood, one going to the spider harness for gauges, and one to the coil????

Thanks for the response.

One option: just temporarily run a wire from the battery to the distributor (or wherever the other end of wire #12 actually connects). This bypasses the switch and all the connections surrounding it. Just remember to disconnect the wire when you are done testing.

 

[EastRidge]

Just about any switch will work. A DPST (Double Pole Single Throw) toggle switch would be fine, if you don't care about looks. In fact, it would be a cheap way to troubleshoot the problem, since the switches only cost a few bucks. The power feed to the switch is wire #11. Connect that to both poles of the switch. The other end of the switch would have the wire feeding the distributor on one pole, and the wire feeding the guges on the other. (I'm not sure why they are fed independently, but that is how the stock ignition switch works.)

Even before replacing the switch, you could just check if the power feed to the distributor (wire #12) has power when the ignition switch is on when the engine will not fire. If there is power there, and the engine is not firing, the problem is something other than the ignition switch.

One other possibility to consider: When the coil starts to go, it can get intermittent, and especially can be affected by heat. Coils can get damaged if the ignition is left on with the engine not running for an extended time.

Have my fingers crossed......thank you for the above,.....good information/tips.

 

[John Mc]

If you do end up needing a new ignition coil, the NOS ones are getting hard to find (assuming you re still running a 24V system). The chrome Chinese ones are hit or miss on the quality. Debella Jeep's aftermarket coils seem to be working out well. I've got almost 10,000 miles on one with no problems

 

[NDT]

You can use a M151 ignition switch with some pigtails.
Don’t forget about the M37’s propensities to vapor lock when hot.

 

[EastRidge]

Have my fingers crossed......thank you for the above,.....good information/tips.

I also have a main battery switch installed....always off when not in use.

 

[EastRidge]

One option: just temporarily run a wire from the battery to the distributor (or wherever the other end of wire #12 actually connects). This bypasses the switch and all the connections surrounding it. Just remember to disconnect the wire when you are done testing.

Looks like it's actually a 4 wire switch. I thought that bare bullet end was referencing ground,.....but it's not. It looks like a termination block, or resistor(?)

Anyways, I found out with it bouncing loose, it has power.....weld flash!

It didn't really bother anything as I then turned the ignition switch on and wha-la....drove it in the shop.

BUT......now, I need to have it fail to fix it.

I may just keep trying the switch until it fails.

For the record, I had instrument power BEFORE disassembly,....started, then died.....as it sits, I can't seem to get it to fail/not work.

 

[John Mc]

If you have a stock ignition switch, it’s a double pole switch - essentially two switches, both controlled simultaneously by one knob. One set of contacts feeds the gauges and the other feeds the ignition. If it is malfunctioning, it’s possible to have power to the gauges but not to the ignition or vice versa.

 

[EastRidge]

If you have a stock ignition switch, it’s a double pole switch - essentially two switches, both controlled simultaneously by one knob. One set of contacts feeds the gauges and the other feeds the ignition. If it is malfunctioning, it’s possible to have power to the gauges but not to the ignition or vice versa.

Well, as far as I can tell, when the gauges work, she'll run......gauges sitting no fire at all.

The back of the switch.......the rubberized filler is all cracked.

 

[GopherHill]

I'd change out the switch because of old age and wear. Might be money well spent.

 

[EastRidge]

Well, as far as I can tell, when the gauges work, she'll run......gauges sitting no fire at all.

The back of the switch.......the rubberized filler is all cracked.

Again, appreciate the words of wisdom....but am in need of more.

Finding an economic toggle switch is proving to be a tall order to fill......but:

If the service rating amperage of a 12 VOLT rated switch is high, as innorth of 20 amperage, would it be fine running 24V?

Again with finding this somewhat unique toggle switch........not wanting to rig this, but have to ask.......could I utilize a "main disconnect" two pole and just individually crimp end eyelet style fittings and stack them on the load side?

Thanks again for any and a help

 

[John Mc]

A quick search on Amazon turned up a bunch of switches that would work ranging from $10-$15. I suspect your local hardware or automotive store also has some in stock. If you can't find DPST switches, you could use a DPDT switch (Double Pole Double Throw). You just won't use a couple of the connection terminals.