Customs VDO electric temp gauge

So, this is perplexing me. The electric temp gauge is spiking to 250 ,and when I turn on the headlight switch it drops to 190 degrees, which is fine.I have replaced the sending unit, no change. I feel like I’m chasing my tail.Thanks in advance. Snowman ⛄️

 

Bet there is a grounding issue

 

I thought so too. Switch or gauge? Snowman ⛄️

 

With the temp sensor on the engine the ground between engine and everything else becomes important. Then again, could be the ground at the gauge that somehow is affected by the current going to/from the lamps...
Anyway, break out the multimeter, see where you get a voltage difference between things that should have exactly the same voltage (i.e. different grounds) with the engine running. Once you've found a voltage difference you just need to narrow it down to where the bad connection causing it is.

 

Will do thanks. Snowman ⛄️

 

First and easiest is to ground your engine block to the chassis or directly to the battery negative (if it is negative earth) with a jumper lead, then see what you get.

 

That’s done. Snowman ⛄️