4 replies to this topic

[Brent]

Got a wierd problem. I fitted a dual USB socket to power a TomTom and a dashcam, all went well and both worked but suddenly the voltmeter on the dash wasn't working. Took it out to check and connected to a 12v battery it worked fine. Then checked the voltage in the car and with the TomTom connected the voltage on some items went down to 8 volts! Thought that fitting a proper cigarette lighter and the original TomTom 12v adapter would solve things. Wired everything up but still the 12 volt line goes down to 8 volts with the TomTom connected - disconnect the TomTom and everything is good again. Anyone have an idea what is happening?

[sonscar]

Too small cable up to where you have spliced the new stuff in,high resistance connection in the same wire?just my thoughts.Steve..

[alpder]

Plug in your TomTom (so you get the 8V issue). Then measure the volts with a DVM between (A) the -ve terminal of the 12V socket and the chassis and (B) the +ve terminal of the 12V socket and the +ve terminal of the battery cable (probably easiest to do where the battery is wired to the starter solenoid).

 

Either (A) or (B) will measure 4V, indicating (A) a high resistance to ground or (B) a high resistance in the wiring to the sockets. Either that, or your battery may be very, very sick indeed.

 

A lot of aftermarket (ebay) ready-wired 12V sockets have chunky-looking wires which, when stripped, turn out to be 90% plastic insulation and 10% conductor. They're not fit for purpose. I prefer to wire my own with nice chunky wires to minimise losses. I've used dozens of ebay item 194261106522 and found them good - the 12V and USB sockets are also available separately without the panel.

 

396231471267 looks neat too, tho' never used one. Might get one for my teardrop.

Edited by alpder, 16 May 2025 - 02:59 PM.

[Brent]

Good ideas - I'll take a +ve lead from somewhere else fed by the ignition

[68+86auto]

Good ideas - I'll take a +ve lead from somewhere else fed by the ignition

It is best to measure the drop as previously described. The issue could be in the earth so you'd be wasting your time moving the positive wiring.

Edited by 68+86auto, 18 May 2025 - 03:16 AM.