Retarder, Cruise control & Engine oil temp gauge

[Robert & Dianne]

Good morning

Before I get too involved trying to locate problems with the retarder, cruise control and engine oil temperature gauge I was wondering if all three of these issues have a common denominator? They all stopped working around the same time.
If it helps to know I have 12 volts at the cruise control switches, do not have 12 volts or a led light at the retarder switch and the temp gauge is at 200 degrees with ignition switch off and 220 with it on. Tested the gauge and it tests ok.

Any suggestions would be welcomed

[Mike Hohnstein]

Ground

[Robert & Dianne]

Do all three have a common ground point or connection?

[Bill Pape]

Originally Posted by Mike Hohnstein

Ground

Battery connections ,,grounds & gage grounds are the best place to start,
But you noted 3 different systems,
although retarder & cruise have some common together parts in a relay box behind the driver headlight.

It may seem unrelated but there are many posts on the ZF needing a full 12 volts to operate properly, which controls the retarder, early ZF installations (87) had a relay mode to insure proper full 12 volts,
Search forum for ZF 12 volts

[Robert & Dianne]

Thank you. I'll start with the relay behind the headlight. I also just put house batteries in with a separate starting battery group I'll recheck the grounds.