74 Road runner 318 auto Rally gauges.

So about a month ago I sent my gauges in to bobs speedometer and he fixed and calibrated my who gauge cluster because my fuel temp oil and batt gauges werent working. I got it back and installed to and now my fuel gauge works and I havent hooked any wires up to the batt gauge. I was expecting this because the previous owner put in a set of aftermarket gauges (temp, oil, batt) and i assumed the others werent hook up properly. Tonight I bought a new electronic oil sender unit and installed it instead of the aftermarket mechanical one. I looped wire around it and then put it in the correct location on the bulkhead. I then check for continuity from the sender unit to the stud on the back of the oil gauge and found out it was continuous. The ground wire on the cluster is hooked up and should indeed be grounding. I start the car up let it run for a couple mins and rev it and the oil pressure reads nothing.

I then did the same thing with the temp sender but i just used the one that was already on the car instead of buying a new one. I did the same thing with the same results as above.

What i thought was weird was that when i checked continuity from the oil sender to the bulkhead under the dash, it would read continuous whether i touched the oil or the temp prong (right next to eachother) on the bulkhead. It only worked for those two, none of the others.

Anyone have any ideas?

Also how do I hook my batt gauge up?

Thanks

 

You lost me, here. Make sure you have a gauge oil sender and not a light oil sender. All the gauge senders I've ever seen are a cylindrical can. If you are doubt, switch off your engine, unhook the sender wire. Hook your meter on ohms to the sender and to ground. It should read at least 73 ohms or more. If it reads really low, it's either bad, or it's a lamp type sender.

Then start the engine and again hook up your meter. Depending on pressure the sender should read anywhere from 40 ohms or less. If it's "open" it's a lamp type sender

You talking about the factory ammeter? IE meter needle is centered? Should be two fairly large studs on the rear of the gauge / meter. Is your harness factory? If it has not been modified, look under there for a large black and a large red spliced and taped together.

 

To clarify that, I checked continuity from the oil sender unit to the bulk head connector. It would beep if i put it in the slot that the oil sending wire went, but it would also beep when i touched the temp slot on the bulkhead connector, which was right next to the oil slot.

I'm pretty sure its the oil gauge sender, I told the guy i wanted the gauge sender not the light. I can take a picture of it tomorrow or ill just test it doing what you said.

As for the ammeter, yes its the factory one where the needle is centered. I see the studs on the back of the gauge but i dont see any wires? this harness is really butchered up though so who knows where that went.

 

OK check it to ground as I told you. What does it look like?

If the harness is butchered, maybe somebody rewired it or did the MAD modification and taped stuff up in there. Consider going to a voltmeter if it otherwise works, and consider rewiring the car in the near future

Some ideas on amp to voltmeter conversion:

Read all three pages, as a number of different cluster styles are illustrated

http://www.forabodiesonly.com/mopar/...ter+conversion

The MAD ammeter bypass:

http://www.madelectrical.com/electri...p-gauges.shtml

You have a factory shop manual?

 

Okay I unhooked the wire that is connected to the oil sending unit and hooked my ohm reader to the unit and grounded and it didnt read anything, just 0. Ill put a picture of the sending unit I bought but the guy at o'reillys assured me that it was for the gauge not the light.

 

I have some here, does your meter only show O (open) "beep" (closed)?

Can it show resistance in ohms?

Oil sender no pressure is 79 ohms.

Temp sender room temp is 218 ohms.

That is from the threaded terminal to the tapered thread (like grounded to block when installed).

 

My meter shows in ohms and i tested it was some resistors and it is accurate. Ill go check the temp sender.



Okay, i checked the temp sender and i switched it to 2k ohm setting and it read .260.
I hooked it up to the oil and it wouldnt read 0 it would read 1.000 no matter what. What am i doing wrong?

 

Well, LOL we need to set some specific conditions

FIRST what model / brand is your meter? I can step you through what to set it on

Second, you must measure these with the wiring UNhooked, and first with engine OFF.

In the case of your temp sender, this is going to matter whether you measure with engine cold or hot. It's "why" they call it a temp sender, LOL

A temp sender should not be either .26 ohms or .26K ohms, which would be 260 ohms. So this does not make sense

The oil sender reading MAY be your meter's way of reading "open" or "infinity." If you set the meter up for resistance, and just don't hook the probes to anything, what does it read? THAT is infinity

With the example meter below,

http://houseofrobos.com/wp-content/u...014/01/dmm.jpg

You want the switch on 200 ohms, at far bottom left "ohms" where the "Omega" symbol is This means the meter will measure "up to" 200 ohms, and will be more accurate at low readings.

Nominally, your senders are as follows:

L = 73.7 Ohms (empty)
M = 23.0 Ohms (1/2)
H = 10.2 Ohms (full)

So for temp, cold, the sender should read at least 73 ohms OR MORE. If the engine is warm, somewhat less, depending

For oil, engine off, sender should read at least 73 ohms OR MORE. With engine running, depending on oil pressure, "somewhat less." I'd expect idle to be between 73 and 23 ohms. If you have a lot of idle pressure 23 ohms or less.

 

Okay somethings not right. Heres my meter. It works perfectly when i test the 68 ohm resistor i bought but not when i hook one end to the temp and the other to the neg batt

 

Sounds to me like the sender is bad. Maybe go back to the store and check one right there with your meter

Is it possible? That you somehow got a sender for a warning lamp? Mopar did use a few of those in some cars, I don't remember what

 

So you think that both my oil and temp senders arent working? Does the warning lamp sender look like the one in the picture? They told me it wasnt the light but maybe they screwed up.

 

Just looked at the photos. They "look" right. Boy, I don't know. What do you have otherwise to try the meter on? You mentioned a resistor.

 

I'm running out of ideas. They look right. Have you tried the oil, at least, with the engine running?

What does the meter display show when set on 200 ohms and the probes hooked to nothing?

 

Yeah i have a bunch of resistors left over from when i was testing my gauges. Im going to try my friends meter tomorrow. I havent put the meter to the oil while its running yet.

When its hooked on nothing it will read the same as when i hook it on eother the oil or temp semder. It reads 1 .0, so im guessing this is infinity.

 

That would be correct.

I could see that the oil sender might be infinity when off, that's why I thought you might check it running.

I cannot see the temp sender being that way. It is what's called a thermister. If you are unaware, this is a resistor which is designed to change resistance with temperature. It is the basis for many, many thermometer applications for decades. Most any outdoor thermometer uses a thermistor of some type.

 

Okay so im back for christmas break and am gonna give this another shot. Im trying to get my oil and temp senders to work but im struggling. I unhooked the wire and put my dmm on the temp stud to the batt ground and checked for continuity but there wasnt any. I took off the temp sensor and checked the resistance through it and it was 360 ohms. Its 50 degrees in my garage. I set it on the heater for a minute and it went down to 250 ohms.

How should I go about testing both the oil and the temp sensor? When you guys check resistance and continuity from the stud to ground what value do you get?

 

I grounded both the leads of the temp sending unit and oil sending unit, turned the key to the run position, and both the gauges were pegged. I measuring the resistance of the oil sending unit while it was running but when i hooked my dmm from the oil sending unit to the ground, it just read infinity or open.

 

I tested water sensor for Lab's Fury at room temp = 262ohms, 186'f = 28.3ohms.

If you were to clip your meter to it and ground, warm the vehicle you should see the resistance fall like you did with your garage cold, heater hot test. I don't think it's a problem.

Your oil sender infinite or open is incorrect, I have one and at 0 pressure it is about 80ohms. If you have one in the block or in your hand it should show that kind of resistance.

If you get an oil sender that works, installing it, starting engine and watch resistance immediately change then your tracing wires through firewall, removing gauge cluster and testing at gauges.

Make sure you have good block to chassis and gauge cluster to chassis grounds.

 

Okay, so I should be able to test the temp sender while the engine is off? Both the oil and temp sending units read open loops when I connect them to ground. Im going to get new ones and see if I just bought a faulty sending unit.

 

I took the oil sending unit off and then measured the resistance through it and it was an open loop.



How can i test to make sure this works?

 

Before you do that try this. January 5th the temp worked out of the block.

Clip onto the temp hex above threads and the stud, what ohms? This would show the thread of the sender is not grounded to block. Know what I mean?

Dan.

You could try a bicycle pump to test.

 

The resistance between the temp sender body and ground is about 1.5 ohms

So this means its grounded to the block right?

Whats the bike pump test?

 

A good ground should be more like 0.2ohms or less. Pump test is some way to pressurize sender and see if resistance is generated.

Touch your leads together and it should be that low.

 

I measured it again and its a constant 1.2 ohms

 

Its 1.0 ohms when i touch the leads together

 

Odd, but ok that's what it is. Any meter I've had and the ones I have now are always below one ohm leads together.

If that's the case it is showing good ground. Mine will do goofy stuff if the battery is low, check to be sure.

 

Its kind of a crappy dmm but I measured a 10, 23, and 68 ohm resistor and it measured them dead on.
I changed the batteries and it didnt change.