A100 temp gauge resistance cable

Hi everybody,

The wiring diagram I have shows a resistance cable between the temp gauge and the sender unit. The wiring on my van has been hacked about and there's no sign of it.

Can anybody tell me what the resistance should be?

Thanks,

Hugh

i think it's somewhere around 400 ohms but ill dig a bit later. a very old post of mine did have it somewhere here.

jkr wrote:i think it's somewhere around 400 ohms but ill dig a bit later. a very old post of mine did have it somewhere here.

could you also go to ,say radio shack and get a resistor of some kind in that value??? to be wired in right before the wire gos on the gauge terminal?? what happens when you use ordinary wire as mine is?? this has been driving me nuts for years,really.id love to hear some input on this one.

So Is 400 ohms correct ? and should the resister be at the gauge ...on the wire going to the sender. Also what if any difference does in make , without the resister ??

the resister keeps the gauge from fluctuating as the temp increases. it will be "hyperactive" without it and read slightly high 3/4 way up...

I've got one more question. I had to add wiring to the engine harness/ about 5 foot. I replaced all of the engine wiring. But nothing from that point up to the gauges. Would you think that I would still need to add the resistor ?

the resistance portion of the wire was from the sending unit back to the gauge unfortunately. how I caught this problem was I did the same as you. I replaced every wire from behind the speedometer to the engine compartment. not a lot of wires but if the voltage regulator stuck "once" it usually overheated the wires from it to the alternator. if you still have your old harness just use the first 3' again. just coil it up under the compartment somewhere.
it will be easy to see the resistance part of it as it is stranded slightly different and a tin covered (stainless) wire versus a normal copper strand type. you don't need the whole thing but if you have it measure the resistance of it and go to an electronics shop and ask for a resistor and add it to the line somewhere. should work fine...

just took mine off and measured it for resistance.............
.......................................................5.8 ohms folks.......................................
so get a resistor with that value, insert it into the wire by the sending unit and then a connector to the sending unit. and as long as your value is somewhere around 5.8 it should function correctly.

Thanks for all of your help, the people and information on this website are first class

jkr wrote:the resistance portion of the wire was from the sending unit back to the gauge unfortunately. how I caught this problem was I did the same as you. I replaced every wire from behind the speedometer to the engine compartment. not a lot of wires but if the voltage regulator stuck "once" it usually overheated the wires from it to the alternator. if you still have your old harness just use the first 3' again. just coil it up under the compartment somewhere.
it will be easy to see the resistance part of it as it is stranded slightly different and a tin covered (stainless) wire versus a normal copper strand type. you don't need the whole thing but if you have it measure the resistance of it and go to an electronics shop and ask for a resistor and add it to the line somewhere. should work fine...

just took mine off and measured it for resistance.............
.......................................................5.8 ohms folks.......................................
so get a resistor with that value, insert it into the wire by the sending unit and then a connector to the sending unit. and as long as your value is somewhere around 5.8 it should function correctly.

Yeah I don't have any of the original wiring at the engine. But I will try to add a resistor at the temp sending unit, and see what that does. My FSM does not show anything about resistance wire for the sending unit ??

just beside the sending unit you see a wwwwww line. that's the resistance

Thanks, like I said my FSM does not show the wavy resistance wire, know idea why it wouldn't.

That schematic is for A100s later than '65. My '65 specifications, p.6, schematic shows an 18 gauge orange wire instead of the 24 gauge black and pink wire. The right side, 4 engine wire harness in my van was replaced with the later year 5 wire harness which includes the solid stainless, black and pink wire to the temp. sending unit. That wire is brittle and it had a break in it, so I cut out the bad piece and spliced it together and was left with a straight run to the sending unit. Also, there is no temperature warning light in my '65, so that other (copper) wire from the sending unit was cut and dead ended, changing the total resistance of the temperature sending circuit. Remember that the sending unit is actually a variable resistor receiving unit to ground. My temperature gauge seems to work fine, but I don't have a resistance value to give.