I have a couple electrical problems with my 140 after I installed all the wiring. I will start with the easy question first … I changed the car to negative ground and also switched the wires around on the amp meter to compensate for the change. Would this negative ground change have any effect on the fuel gauge at all?
No, not if you have an original gauge. It won’t care.
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Thanks Eric … and I am very pleased that you answered this question as my next question seems to be right down your alley. I have read your past information on the DR1 wiper motor and I still don’t understand. So … first of all is the drawing on page 322 of XK 140 Explored correct. I have used that as my guide and I seem to have some problems. Not sure if it is the switch or what, however when I apply power to the system in Park G[5] & GP[1] are hot. When I switch it to either Normal and/or High G[5] & BG[2] become the hot lines. Should that be the case? Also, with no wires connected to the motor there is continuity between GP[1] , BG[2] and WG[3] wires. So, I am not sure if the wiring drawing is incorect; if the switch is screwed and/or if the motor is screwed or all of the above 
I can’t see anything wrong with the drawing on page 322 of XK 140 Explored except that on the switch, terminal 1 has not been marked. This is the terminal the black ground wire is connected to. You have to be careful with the PRS7 here, because there is no terminal 9. The numbering goes from 8 to 10 counting clockwise.
In park, you are right, 5 & 1 are hot so that is G & G/P. You don’t mention it but at the same time, 2 & 4 should be connected - these are U/G and G/B. And there should be a ground via the park switch until the park position is reached. If any of these conditions are not met, the motor will not run backwards.
Your observation for normal is also correct; 2 & 5 should be hot. So, U/G & G. Also, 4 & 1 should be connected together and grounded. So G/B & G/P are joined together and grounded via the black wire on switch terminal 1
Finally, yes, you should see some form of continuity between 1, 2 & 3. Between 1 & 2 you should see the field coil resistance and between 1 & 3 you should be able to measure the resistance of the fast speed resistor.
Hope that helps.
Thanks Eric
I have rechecked the wiring on the switch and it is correct to what you have said with the black wire fastened to terminal #1. When I checked the current to the motor I had all the wires disconnected from the motor. If I am understanding correctly my switch seems to be working correctly even though there is no current difference between Normal and High using the method I used? Is there a way I can apply an outside source of current to a couple of the terminals on the motor to see if it turns over.
If you email me at mcculloughh@shaw.ca I will email you some photos to take a boo at and might make more sense once you see what I did.
Cheers
Harv McCullough
Chilliwack BC
Canada
Yes, the quick way is like this, assuming you have the cables correctly connected to the motor. Join 1 & 4 together (G/P & U/G) and connect to ground or one side of a battery or power supply. Then join 2 & 5 together (B/G & G) and connect to the the 12 volts supply or other side of battery etc. If you do this and the motor doesn’t run, there is something wrong with the motor. I would suggest the thermal cut out but you’ve checked for continuity between 1 & 2.
Thanks Eric. Guess I am a bit thick when it comes to this electrical stuff so lets start with the switch to see if it is functioning correctly. I have all five wires disconnected from the motor and I have checked the continuity on all the wires with the switch in its three different positions. On Park position there is continuity between number 1 & 5 and also between 2 & 4 and no continuity from ground to any of the wires. On Normal position there is continuity between 1 & 4 and also between 2 & 5 along with continuity between ground and 2 & 5. On the High position there is continuity between number 1 & 4 and also between 2 & 3 along with continuity between ground and 2 & 3. Armed with this information does the switch appear to be functioning correctly?? If so then my next step would be to apply power to the motor from an external source to check to see if it actually functions. I want to leave the five wires from the switch disconnected and just apply a hot and common wire to the motor to see if it will work. I don’t seem to understand what you explained on your last description, but as I mentioned I am thick when it comes to auto electrics.
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I have the supply and the ground round the other but for testing, it doesn’t matter. If you have the wires disconnected from the switch just join the two pairs together, (BG & G one pair), U/G & G/P the other pair. Connect 12 volts between one pair and the other pair and the motor should run.
OK … so if I understand this correctly I could also do this at the motor by applying power to the combined BG & G wire terminals and the other side to the combined UG & GP wire terminals? I don’t have the wires disconnected from the switch right now and if the switch is functioning correctly I would like to leave well enough alone. So just as a follow up, does the switch appear to be functioning correctly as per the way I explained the continuity in the above message?
Yes, the switch seems to be working correctly. Test the motor without it being connected to the switch. So if you’re leaving the wiring to the switch in place, disconnect the wiring from the motor.
Thanks so much Eric for all your help with this and stay safe.
So Eric … I did as you suggested with running power directly to the motor and it does run. I then hooked everything back up again through the switch and it doesn’t do anything at all. As you said, the switch is functioning as it should so I am now assuming there must to some type of an internal problem within the electric motor?
In the knowledge that the motor is OK, I think my next move would be to put the switch to normal so that the motor should be running and then go to the motor with a multimeter and see what is missing, checking for a supply on 2 & 5 and a ground on 1 & 4. One or more of those must be absent or the motor would be running.
OK … here we go checking for current with ignition on and switch on Normal … between #2 & #5 - no; between #1 & ground -yes; between #4 & ground - yes; and also between #5 & ground - yes; between #2 and ground - yes. With the switch in Park I get the very same readings? Wonder if it is the switch and if I should just go ahead a purchase a replacement?
I’m slightly confused about what you’ve done. Try this: with the ignition on and the switch in normal, with your multimeter measure the voltage between 2 and ground and then between 5 and ground. In both case, you should see 12 volts. Now measure the voltage between 1 and ground and then again between 4 and ground. If you see any voltage on either, this indicates that a ground is missing. If you see no voltage on both of these, turn the ignition off and measure the resistance between 1 and ground and also between 4 and ground. The expected value is zero or near enough. All these conditions must be met or the motor will not run.
Ok … thanks to your advise I now sorted it out and everything is working as it should be. When I measured the voltage between #1 and ground, along with #4 and ground I was getting voltage. I then checked continuity on just the black ground on the switch to ground and I was getting nothing. Believe it or not, when the dash loom was made, then didn’t remove the insulation from the wire and they just clamped the connector on, hence no continuity. I repaired that and now it is working as it should do. Finally all the electrical is now working and I can put all the dash back in. Again … thanks so much Eric for all your help.
Excellent. Glad you fixed it. Now you can get on with all the other jobs!
Yes Eric … there’s a lot of truth to “all the other jobs”. Eight years and counting for me 