Posted: Sun Jul 26, 2009 10:39 pm Post subject: Temp gauge and Ammeter
Hi Guys,
My M38A1 runs great but only the fuel gauge works. The pressure gauge I think works , it reads 60 when powered up and grounded to the block, it needs a 0-60 sender because the new one I have installed is either 0-120 or doesnt work. Is there a way to get the ammeter to work with the solid state voltage regulator or do I have to switch it over to a voltmeter? And finally is there anyway to check to see if the temp gauge is operational? Its been a long haul and it feels great to be here with these problems. Thanks in advance.
Be sure to use the link and printout the instrument troubleshooting TB.
The gages must have their cases well grounded. The instrument cluster does not ground well with the 1/4 turn fasteners. It pays to add a ground wire from one of the lamp mounting screws to each gage housing and to the main dash or firewall. Sender grounding is just as important. The oil pressure and water temp senders have very good metal to metal grounds. The fuel tank needs some help with a ground wire added from one of the sender mount screws to the tub.
The pressure sender is difficult to test because you need an accurate presure source/tester. I prefer to temp install a civvy direct read oil pressure gage and then remove it and install the electrical set and compare the readings.
The water temp sender can be placed suspended in a coffee can with water and a thermometer and the can heated while watching the thermometer and comparing results in Ohms to the TB. Don't forget to add a ground jumper from the sender to a good ground.
The original mechanical voltage regulator had a shunt installed behind the connector housing on the regulator. The two wires #8 & #9 were connected to the shunt and they sent a light induce voltage signal to the amp meter based on the main current flow through the shunt.
The later transistorized regulator has no shunt in it so #8 & #9 wires are useless. The voltmeter is a more informative system meter then the amp meter ever was. So the switch should not be a painful one. Buy the gage and install it in the cluster. Connect it's hot lead to the #27 spider harness. This is easier to do if you buy a 5 wire #27 spider harness.
Yes you could retain the amp meter by installing a amp meter shunt of the same value in the power feed from the regulator wire #4. Then remove #8 & #9 from the plug on the regulator and attach them to the two small terminals on the shunt.
The item AA is the spider. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
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