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Sending unit testing

dakonthemountain

California Chapter member
Hey guys,
I'm FINALLY getting to some of Burt's needs... Unfortunately, I've left my shop manual for electronics up at the mountain house.....:headbang: I know where the sending unit is for the temp gauge on the manifold, but I don't know how to test it?... I've got testers, ohm meters, etc., but my electrical knowledge is limited. How do I find out if it's the sending unit? I'd MUCH rather replace that than having to take the dash out to replace the gauge itself.. I've got another gauge from the junk yard I could wire up, but I don't know if it works either.. Secondly, I've also got to find the sending unit for the charging system and test that. I have a new internal voltage regulator for the dash also if I need that, but hope I don't! It's wierd though that both gauges stopped working at the same time... The fuel and oil pressure gauges work fine.

any ideas? Thanks in advance!
Dak
 

Fellro

Moderator
Staff member
The temp sender changes resistance with temperature, if i remember correctly, the resistance is higher cold than when warm. there is no "sender" for the charging system, it is just an ammeter that reads the current flow. The current being used by the truck all comes through the ammeter, then back to be distributed. I myself prefer voltage gauges over ammeters mostly for that reason, you get less volt drop due to less distance to travel. More distance = more resistance, more volt drop.
 

gsxr1238

Be fast.....or be last.
Pull the lead wire from the sender and ground it(key on or powered),if the lead wire and the gauge are good the gauge will peg.This is a test for the w/t gauge.The ammeter gauges (stock) were not at all reliable.A seperate ammeter or voltage gauge is the way to go there.
 
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Continuity to ground SU's

The Temp S Unit is a prime example of the hotter it gets the less resistance to ground and the higher the needle rises on the gauge

Remember that too much teflon tape on the threads of an SU can negate the grounding principle.

A small piece of debris on the small orifice can prevent the OIL Pressure SU from showing pressure on the guage.

Always check the wiring to the SU first by doing the Light tester to the wire and watching for a pulsing 5 volts to the connector.

 

gsxr1238

Be fast.....or be last.
If you you will use a liquid teflon or pipe sealant on the pipe thread joints you will not have this problem.Loctite makes a good teflon sealant.And the best is a sealant called Rectorseal 2 that plumbers use to seal natural gas and water line connections.Will remain pliable and flexible.Best stuff to use where anti-freeze is concerned.
 

dakonthemountain

California Chapter member
Thanks gsxr1238, That is what I use on my pipes also. I didn't realize I could use it on the truck also! But I will! I'm back up the mountain now and won't be able to get back to my truck until next weekend though...

I'll update on my progress when I get back to it.

Thanks again all!
Dak
 

bendog

Pacific Northwest Chapter member
Mistaken on all current passing thru the ammeter, its a shunt, current is measured off of the extra length of wire wrapped up into the loom between the alt/harness. Actual draw is measured off of that. The guage is less than reliable as stated. A few "other" manufacturers did it that way, very dangerous 100percent of electric draw passing thru the guage, in the cab=fire hazard.
Just pondering here, but you could bring a small camping style burner with a pot of water and a cooking thermometer to read the temp off of and verify your temp guage reading (don't forget to ground the sender)?
 

dakonthemountain

California Chapter member
Hi all,
Well I FINALLY got to the temp sending unit. Thank goodness it was just the sending unit and not the gauge. Of course the biggest pain was draining the radiator, but I took the opportunity to flush and replace the antifreeze at the same time. FIXED! Yahoo!! Works great! Now I want to test the ammeter. I know that it's a shunt type from my shop manual and under the testing section it states to "check the battery to circuit breaker wire connections" For the life of me I cannot find that wire or a circuit breaker. I really want to try this before I go through all the trouble of replacing the gauge by taking out the dash. That's a pain to do. I know from replacing the instrument pod a number of years ago. I suppose I can look further in the manual for the wiring diagrams, but I'm lazy and thought I would ask here firstsmilieFordlogo

Any ideas here?.. Thanks!
Dak
 
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