Test Light

Hi All, 
Apologies if this posts twice, i got an error message the first time.  
I've got the E-book and was also watching Paul's video where he used a test light hooked to ground to jump a switch. 
If having a test light hooked to ground essentially gave you a ground jumper wire, does that mean if you had it hooked to battery positive, you would have 12v at the tip? I feel like i'm missing something as surely this has the potential to be dangerous if for example your wiring diagram was incorrect and you probed say a 5v ref circuit instead of a ground, jumping it 12v? Similar to pressing up on a power probe?
Appreciate any responses, I'd never given it any thought before but i've definitely seen people probing random wires in order to figure out which wire is which without a diagram which makes me think, maybe the resistance of the bulb prevents any damage?
Thanks in advance,
Alex

If having a test light hooked to ground essentially gave you a ground jumper wire, does that mean if you had it hooked to battery positive, you would have 12v at the tip?

Essentially, yes. However, you will have a slight voltage drop, depending on the resistance of the test-light.

this has the potential to be dangerous if for example your wiring diagram was incorrect and you probed say a 5v ref circuit instead of a ground, jumping it 12v? Similar to pressing up on a power probe?..... maybe the resistance of the bulb prevents any damage?

Exactly. That is why using a test-light is much safer than a power-probe. The resistance of the bulb is MUCH more forgiving than the 10 amp circuit breaker of the PP.

Nothing is fool-proof, and you should always understand the circuit that you are testing, but modern circuit designs are pretty resilient.
I have never, personally, seen any damage done by a test-light, but I HAVE, however, fried modules with a Power-Probe.
 

Thanks for your response, i 100% agree to always understand the circuit you are testing, but i've definitely been guilty of being lazy and not checking a diagram for circuits like washer pumps. A lot of Toyotas share one pump for front and rear. They're usually 2 wire pumps and depending which side is grounded, will operate the appropriate front/rear. So in the past i've just gambled which one will be power and which is ground and not thought of the possible issues of me essentially jumping 12v. But going back to you saying about the bulb resistance, i presume that makes the test light inherently safe so i *shouldnt* run into any issues doing that? However may just be safer to always double check.