Wiring or electrical problem

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steve1973
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Wiring or electrical problem

Unread post by steve1973 » April 16th, 2017, 3:56 pm

Hello all,
I'm just finishing up installing a new front wire harness from Vintage Wiring of Maine. Everything seems to work but I do have one problem. When I go to start the jeep and press the foot switch and release the starter stays engaged and running. When I turn the switch off and back on the starter kicks in without pressing the foot switch. All switches have been replaced and tested. I even tried putting in the old switches with same results. I retraced all wires and are in correct locations. So here's the interesting thing. I traced back to a oil sensor switch, not the oil pressure, and not sure what it does. Two wires, number 77, and wire 77B got to this switch through a plug.

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When I unplug from the switch everything works fine. So I'm at a loss of what to do next. Is the sending unit the problem? Do I really need to have this plugged in? I need your help. One more thing. It ran fine before I changes the wiring harness but wires and connections were questionable.

Steve A.

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Horst
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Re: Wiring or electrical problem

Unread post by Horst » April 16th, 2017, 4:46 pm

I am not an A1 guy but that is the oil pressure switch turning on the fuel pump. Only when the engine is cranked or runs, the in-tank electrical fuel pump will run. However your picture shows a mechanical fuel pump. I assume you don't have an electrical pump anymore? So that safety switch should not make any difference. What model do you actually have, A1 or A2? That switch has nothing to do with the starter.

On the starter problem, there is no connection of the ignition switch to the starter. The foot switch is routed directly between battery and starter. You must have gotten some stuff wrong when installing the harness unfortunately
Horst

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Mr. Recovery
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Re: Wiring or electrical problem

Unread post by Mr. Recovery » April 16th, 2017, 6:50 pm

From your photo it looks like you are running the manual fuel pump and not the in tank pump, if that is true then you don't need to hook up the oil pressure switch, it is only needed to run the in tank pump when you are cranking the engine and the oil pressure is low, it also acts as a fuel pump shut off if you loose oil pressure.

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rickf
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Re: Wiring or electrical problem

Unread post by rickf » April 16th, 2017, 7:36 pm

BUT! For the 1200.00 plus dollars you paid for that harness it should be right in case you ever get the right fuel pump. On a stock A1 when you push the starter there is a wire that energizes the fuel pump while the starter is cranking. That is the only connection between that plug and the starter and those wire would not hold the cranking amperage for very long. Plus there is a circuit breaker behind the dash in that circuit that would blow if starter current went through it. It certainly sounds like there is an added on starter relay in there somewhere because that starter switch is on or off and the ignition switch has nothing to do with it. It will crank the engine whether the switch is on or off so if you are turning the switch off and the engine stops turning but starts again when you turn the switch on then something has been added in.

Ok, I was just looking over my diagram and the only way I see that the starter can get power through that circuit assuming there are no other add ons is if either you plugged in the safety switch wrong or he wired the plug wrong and when oil pressure builds up it close the circuit between 77A and 77B instead of 77A and 77 as it ids supposed to. Did you run the other end of 77B to the starter terminal? If yes that is right.
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Re: Wiring or electrical problem

Unread post by steve1973 » April 16th, 2017, 8:17 pm

Wow!! Who would of known. This is my Dads M151A1 and I'm helping him with this wiring project. I'm mainly a halftrack guy and int the process of putting a new wiring harness in my M2A1. The jeep also has an A2 windshield. I will pull the driver's seat of and take a better look at the gas tank. He only wanted the front harness change at this time. I will also take another look at the schematic. One question though. Since the engine has a mechanical fuel pump is it from an A2 jeep or was there a block off plate and a mechanical fuel pump added? Did the A2 jeeps have that oil sensor with a mechanical fuel pumps?
Thanks for all your help.

Steve A.

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rickf
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Re: Wiring or electrical problem

Unread post by rickf » April 16th, 2017, 9:19 pm

The A2 would have a plug in place of the safety switch and the A2 wiring harness would not have the #77 circuit. The A1 would have had a vacuum pump where the fuel pump is now and I can see the vacuum line is still there. The fuel line would have come out on the drivers side through a hole to the right of the wiring harness looking at the firewall. If it has an A2 windshield then the usual place to get power for the wipers was the fuel pump wire if the pump had been changed. If that was done then the 77A and 77 would be jumpered at the safety plug. Or you would only have wipers when it was running which is really only when you need them anyway.
1964 M151A1
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Re: Wiring or electrical problem

Unread post by Fil Bonica » April 16th, 2017, 10:32 pm

if the system works correctly when it is disconnected then I would leave it that way.
If necessary , wire a new line for the electrical wiper motor.
its unfortunate that you didn't speak up before because you could have used a much less expensive NOS A2 harness.
You aren't using some of the A1 harness features.

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Re: Wiring or electrical problem

Unread post by Hambone » April 17th, 2017, 8:26 am

As for the fuel pump, the A1's had electric in-tank pumps with oil pressure safety switch, the A2's had mechanical pump mounted to the block, the A1's had a vacuum pump mounted to the block to run the wipers.

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Re: Wiring or electrical problem

Unread post by steve1973 » April 19th, 2017, 7:36 am

Thanks to everyone's input. I learned a lot. Also from the members on the G503 forum site. Here is some photos of the gas tank. You can clearly see a cut wire that has been tied back.

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It also looks like one port is silicone over.

Steve A.

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Re: Wiring or electrical problem

Unread post by rickf » April 19th, 2017, 9:30 am

I see that someone added in a ground to the sending unit so they knew what they were doing with the electrical. I think Daves answer on the 503 hit the nail on the head. It is basically the same as what I was thinking.
1964 M151A1
1984 M1008
1967 M416
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12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

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Re: Wiring or electrical problem

Unread post by fergrn37 » April 19th, 2017, 9:55 am

Might want to find a better plug than RTV. RTV and gas don't do so well together.
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rickf
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Re: Wiring or electrical problem

Unread post by rickf » April 19th, 2017, 10:15 am

What that is covering would have been the electrical connector for the fuel pump. That does not mean it was not gutted and there could be gas present there though.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

steve1973
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Re: Wiring or electrical problem

Unread post by steve1973 » April 19th, 2017, 11:53 pm

rickf wrote:I see that someone added in a ground to the sending unit so they knew what they were doing with the electrical. I think Daves answer on the 503 hit the nail on the head. It is basically the same as what I was thinking.
The ground wire is my idea. I've learned long ago about bad grounds and gas tanks.

Steve A.

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